c 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 10.1002/14356007.a25 345.pub2 Sugar 1 Sugar Hubert Schiweck,S¨ udzucker AG Mannheim/Ochsenfurt, Mannheim, Germany (Chap. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 22 and 23) Margaret Clarke, Sugar Processing Research Institute, Inc., New Orleans, Louisiana 70124, United States (Chap. 20) G¨ unter Pollach, Gross-nzersdorf, Austria 1. Terms, Distinguishing Criteria, Uses, Nutritional Physiology .... 2 2. History .................. 3 2.1. Development of the Cane Sugar Industry ................. 3 2.2. Development of the Beet Sugar Industry ................. 4 3. Properties ................ 5 3.1. Physical Properties of Crystalline Sugar ................... 6 3.2. Physical Properties of Aqueous Sugar Solutions ............ 6 3.3. Chemical Properties ......... 7 3.4. Sensory Properties .......... 7 4. Sucrochemistry, Chemical and Enzymatic Synthesis ......... 7 4.1. Sucrochemistry ............ 7 4.2. Chemical and Enzymatic Synthesis 8 4.3. Plant Biosynthesis ........... 8 5. Methods of Analysis ......... 9 6. Sugar Beets: Cultivation, Harvesting, Preparation ....... 10 6.1. Cultivation ............... 10 6.2. Chemical Composition and Beet Quality .................. 11 6.3. Preparation ............... 13 6.4. Delivery and Storage ......... 13 6.5. Thick-Juice Storage ......... 14 6.6. Weighing and Sampling ....... 14 6.7. Internal Transport, Washing .... 14 6.8. Processing Wash and Flume Water 15 6.9. Slicing Beets .............. 16 7. Production of Juice (Extraction) . 17 7.1. Principles ................ 17 7.2. Extraction Technology ........ 19 7.3. Extraction with Nonaqueous Solvents ................. 20 7.4. Extraction Systems .......... 20 7.4.1. BMA Extraction System ....... 20 7.4.2. Extraction with the DdS Slope Diffuser ................. 21 7.4.3. Extraction with the De Smet System 22 7.4.4. The RT-5 Continuous Extractor ... 22 7.5. Pressing Extracted Pulp ...... 22 8. Juice Purication ........... 23 8.1. Lime–Carbon Dioxide Treatment 23 8.2. Other Juice Purication Processes 29 8.2.1. Simultaneous Defeco-Carbonation . 29 8.2.2. Braunschweig Juice Purification .. 30 8.2.3. Defeco - Carbonation with Interme- diate or Post Main Liming ...... 30 9. Evaporation of Thin Juice ..... 30 10. Production of Sugar from Thick Juice .................... 33 10.1. Production of Massecuite ...... 33 10.2. Evaporating Crystallization .... 34 10.3. Mixing of Massecuites and Cooling Crystallization ............. 36 10.4. Factors That Influence Rate of Crystallization ........... 36 11. Separation of Sugar from Massecuite ................ 37 12. Preparation of Rened and White Sugar ................... 37 13. Working Schemes of Various Sugar Factories ................ 38 13.1. Operation of a Ra Sugar Factory .................. 41 13.2. Operation of a White Sugar Factory – Standard Liquor Process 41 13.3. White Sugar Factories with a Renery Scheme ............ 42 13.4. Rening ................. 42 14. Ion - Exchange Processes in the Sugar Industry ............ 42 14.1. Softening of Thin Juice ....... 43 14.2. Exchange of Alkali Ions for Alkaline - Earth Ions ......... 43 14.3. Separation of Molasses into Sugar and Nonsugar Fractions (Ion Exclusion) ............ 44
The word sugars is the general term used in car-bohydrate chemistry for all nutritive mono- anddisaccharides such as glucose, fructose, galac-tose, maltose, and sucrose. Sugar is the techni-cal and legal name for the disaccharide sucrose[57-55-6], (EINECS no. 200–334–9). Irrespec-tive of whether cane or beet is the source, theterm sugar is used both in technology and infood laws. However, commercially a distinctionis made between cane and beet sugar.
The chemical and physical properties of crys-talline sugarmade from cane and beet are largelyidentical. Slight differences exist only in the typeand mass of the individual nonsugar substancesthat are enclosed in the sugar crystal or adsorbedon its surface (e.g., raffinose, theanderose [16],betaine, amino acids, potassium, sodium, cal-cium, or flavor- and taste-imparting substances).On the other hand, the 13C/12C abundance ra-tio (δ-13C value) varies; it is ca. 11.3 ‰ for su-
crose from cane and ca. 25.2 ‰ for sucrose frombeet [17].
The origin of sucrose (i.e., cane or beet) canbe determined unambiguously from this differ-ence. It is attributed to the varying CO2 fixationin the photosynthesis of sugarcane, a C4 plant,and sugar beet, a C3 plant [18]. However, a de-tection of unauthorized addition of cane whitesugar to beet white sugar is limited by the vari-ation of δ-13C values.
Apart from the δ-13C value, the δ-D/H andthe δ-18O/16O values are also gaining consid-erable importance as analytical determinationtools, e.g., for detecting the unauthorized ad-dition of sugar to fruit juice, honey, or wine(enrichment or chaptalization, after the Frenchchemist F. Chaptal). With the help of these val-ues, it is possible to assign a sugar sample toa definite area of cultivation. For instance, theaddition of beet sugar from Michigan to orangejuice from Florida, or the enrichment of must(wine) with beet sugar, can be detected unam-biguously (Martin process) [19].
Sugar 3
In the carbohydrate metabolism of the plant,sucrose plays an important role as the firstnonphosphorylated compound. According tosome calculations, plants synthesize 150×109
t of sucrose in one year as an intermediate prod-uct. In some juices from plant parts, the su-crose stored as a reserve substance accounts forup to 75% of the solids. These plants serve asraw materials for the isolation of sugar. Theyare mainly sugar beet and sugarcane and, to amuch lesser extent, dates [20] (Iraq, Iran, and theNear East), sweet corn [21] (Middle America),sweet sorghum [22] (Europe, North and SouthAmerica), maple trees [23] (North America andCanada), and palms [24] (India).
Sugar is used predominantly in the produc-tion of food and beverages. The amounts addedrelative to the finished product vary consider-ably. They range from 70–80% in hard boiledcandies, to 40–50% in chocolates and jams, ca.20% in cakes and pastries (pound cake, etc.),10% in carbonated beverages and soft drinks,and ca. 1% in toast.
As a component of a formulation, sugar offersthe following factors:
1) It confers sweetness on products and, afterhydrolysis, participates in formation of theproduct-specific flavor and browning crustcolor (Maillard reaction, Strecker degrada-tion, and caramelization) (→ Foods, 1. Sur-vey)
2) It is a bulking (bodying) agent,which substan-tially influences the texture andmouth feelingof the products during consumption
3) Sugar is also important from a nutritionalpoint of view
In some countries, sugar accounts for morethan 10%of the daily intake of calories (see Sec-tion 23, Table 18). Some nutritionists considera sugar consumption of > 10% of the daily in-take of calories as too high. However, evaluationof the literature (e.g., for the U.S. FDA, UnitedKingdom, and Germany) has shown that exceptfor the formation of caries, no scientific reasonsexist for condemning a higher sugar consump-tion [25].
Sugar is used, for example, as a sub-strate for the production of ethanol (→ Ethanol,Chap. 5.1.1,→ Ethanol,Chap. 5.1.2), citric acid(→ Citric Acid, Chap. 4.3), yeast (→ Yeasts),amino acids (→ Amino Acids), enzymes (→
Enzymes, Chap. 3.1), and antibiotics (→ Anti-biotics, Chap. 5.4.2). For these biotechnologicalprocesses, sugar is often employed in the formofmolasses (see Section 22.2). Sugar can be con-verted enzymatically to isomaltulose (→ SugarAlcohols) and leucrose.
In Brazil, bioethanol is produced on a largescale from sugarcane raw juice (ca. 10×106 t/a)and used either directly as a carburetor fuel oras a gasoline–ethanol mixture (up to 20 vol%ethanol). The European Union supports the useof biofuels with the directives 2003/96/EC and2003/30/EC. The target is to produce 5.75% ofthe total fuel consumed in the EU from renew-able energy sources by 2010 [26]. (→ Ethanol;→ Automotive Fuels).
2. History [27]
Since time immemorial,man not only has cravedsalt but also had a desire for sweet food.Whereasthe consumption of salt (electrolyte) is a phys-iological necessity, the desire for sweet foodis associated with an adequate intake of calo-ries. Sweet, naturally occurring products, suchas mother’s milk, honey, and fresh and driedfruits and their juices, not only are consideredgood and healthy, but also often have a high en-ergy density.
Before humans were able to produce sugarfrom plants, honey and concentrated grape andfruit juices (which can be stored safely for a longtime) were the sole sweeteners.
Rock drawings found in the Arana caves(eastern Spain, ca. 8000 b.c.) show how honeywas collected from wild bees. Similar depic-tions of the collection of honey and the mak-ing of thickened grape must concentrates havebeen found in drawings in Egyptian tombs dat-ing from 2600–1600 b.c.
2.1. Development of the Cane SugarIndustry
On the Indian subcontinent, the practice ofchewing and sucking bits of cane was popular inearly days. According to recent research, sugar-cane has been cultivated in New Guinea since8000 b.c. It traveled from there to Indochina,
4 Sugar
Table 1.Main beet and cane sugar producing countries (2002–2003) [28]
Beet sugar Raw sugar, 103 t Cane sugar Raw sugar, 103 tFrance 5140Germany 4366 Brazil 22 540United States 4046 India 21 900Turkey 2345 China 10 200Poland 2195 Thailand 7300Russia 1740 Australia 5370Ukraine 1550 Mexico 5230United Kingdom 1538 Pakistan 3940Italy 1532 United States (including Puerto
Rico)3594
People’s Republic of China 1350 South Africa 2760Spain 1288 Cuba 2200The Netherlands 1112 Philippines 2160Belgium/Luxembourg 1108 Indonesia 1750Subtotal 29 310 88 944Total 118 254
and finally, to the Bay of Bengal, where it wascrossed with native wild species in India.
Much later, about 5000 b.c., a sugar syrupwas prepared by pressing or boiling cane andthickening the juice. This type of sugar produc-tion was practiced for thousands of years. Theart of producing solid sugar from cane was de-veloped in India about a.d. 200–400.
Through the campaigns of Alexander theGreat in India (327 b.c.), information about sug-arcane first reached Europe.
The cultivation of sugarcane spread from In-dia to China (200 b.c.) and Java, as well as toSicily and Spain via Persia and lower Egypt.The Egyptians had a developed sugarcane in-dustry as early as a.d. 1000 and became themasters of their former teachers, China, Per-sia, and India. However, the sugarcane culturesin Syria, Egypt, and Cyprus were, for the mostpart, destroyed by the Turkish campaigns in the15th century. The Portuguese Prince Henry theSeafarer transplanted sugarcane from Sicily toMadeira in 1420 and laid the foundations for aflourishing industry on the Canary Islands. Onhis second voyage in 1493, Christopher Colum-bus brought sugarcane from the Canaries to His-paniola, which was later called Santo Domingo.Thus, the foundations were laid for the powerfulsugarcane industry of the West Indian Antilles,the sugar islands, which supplied the Europeanmarket for centuries. Sugarcane then traveledvia Middle America to South and North Amer-ica and to almost all tropical and subtropical re-gions.
Since the cultivation of sugarcane is very la-bor intensive, a flourishing slave trade had de-veloped between Africa and America by the be-ginning of the 16th century. This trade broughtwith it social, political, and economic problemsthat finally led to the abolition of slavery in thesecond half of the 19th century.
Sugarcanewas introduced into Europe in a.d.996. As a result of the spread of trade relations tothe Arab countries and, above all, the Crusades(1096–1291), sugar quickly became known andappreciated as both a medicine and a luxury ar-ticle. The European sugar trade was controlledalmost exclusively by the Republic of Venice.With the decline ofVenice after theThirtyYears’War, the sugar trade was taken over by Hollandand, later, by England.
The main cane sugar producing countries arelisted in Table 1. In Europe, sugarcane is culti-vated only in Spain.
2.2. Development of the Beet SugarIndustry
While studying the isolation of sugar fromnativeplants in Berlin, Andreas Sigismund Marggraf(1709–1782) discovered in 1747 that the sugarpresent in beet root is chemically identical tocane sugar. He also isolated d-glucose (dex-trose, grape sugar) from grape juice (→ Glu-cose and Glucose-Containing Syrups, Chap. 1).Publication of this important discovery laid thefoundation for the European beet sugar indus-try.Marggraf also indicated how sugar could beisolated from beet and recognized the economic
Sugar 5
importance of this branch of industry. However,his discovery remained virtually unused in hislifetime.
Franz Carl Achard (1753–1821) recognizedthat a beet with a high sugar content is necessaryfor economic sugar production.
Achard developed selection–breeding meth-ods that are still valid. In addition, he perfectedthe technology of sugar isolation and, after over-comingmany difficulties, was able to present thefirst sample of beet sugar to the Prussian kingFriedrich Wilhelm III on January 11, 1799. In1801 a sugar factory was built in Kunern, andit was put into operation in April 1802. Aftercompleting his campaign, Achard described hisexperiences in a paper published by WilhelmGottlieb Korn, “Instructions for the Cultivationof Beet Used in Sugar Production and for theProfitable Isolation of Sugar from Beet,” whichappeared in Breslau in 1803. However, the ex-pected economic success failed to materialize.The factory burned down in 1807 and was notrebuilt [29].
Table 2. Solubility of sucrose in pure water under normal pressure,according to [34] *t, ◦C S, wt% Lt
* As calculated from the equationS = 64.447+8.222·10−2t+1.6169·10−3t2
−1.558·10−6t3−4.63·10−8t4. S = weight percent of sucrose,Lt = g sucrose per g water.
As a result of the continental blockade im-posed by Napoleon on England in 1806 anddelivery problems for the cane sugar indus-try resulting from the slave rebellions of 1791,some sugar factories were set up in Germanyand France. However, most of them had to beclosed down after a short time because they didnot operate profitably. The French sugar indus-try fared better because it was strongly sup-ported by Napoleon. Only the sugar factoriesfounded after 1831 endured. The ZuckerfabrikWaghausel/Baden of Sudzucker AG, founded in
1837,was operated during a period of nearly 160years, until 1994, and was the oldest beet sugarfactory in the world in operation at the end ofthe 20th century.
The main beet producing countries are listedin Table 1. In the United States, the People’sRepublic of China, Spain, Pakistan, Japan, andUruguay, sugarcane and sugar beet are cultivatedside by side. As compared with 1990, the frac-tion of beet sugar declined from 38% to 25% ofthe total production and a further drop is to beexpected in the future (see Section 23).
3. Properties
The conformation of crystalline sucrose isshown in Figure 1. The glucose portion hasthe 4C1 chair form (→ Glucose and Glucose-Containing Syrups), and the fructose por-tion the 4T3 twist conformation (→ Fructose,Chap. 2.1). The two rings are almost at rightangles to each other. Strong intramolecular hy-drogen bonds exist between the 6′-OH group offructofuranose and the ring oxygen of gluco-pyranose (189 pm) and between the 1′-OH offructose and the 2-O of the glucose moiety (185pm). Since the two glycosidic hydroxyl groupsare linked in etherlike fashion to each other, α-1→ β-2, sucrose is a nonreducing disaccharide.
Figure 1. Conformation of sucrose
The specific rotation of sucrose in water is[α] 20
D =+ 66.529◦ [12] (measured at a concen-tration of 26 g filled to 100 cm3 with water, butrecalculated to c = 1 g/cm3 and 1 dm of opticalpath length).
6 Sugar
Table 3. Density of aqueous sucrose solutions (in g/cm3), according to [35]
* Values extrapolated below the temperature range of the measurements.
The IR spectrum of sucrose exhibits charac-teristically sharp bands at 1010, 990, 940, 920,870, and 850 cm−1 and wide bands at 680 and580 cm−1.
3.1. Physical Properties of CrystallineSugar
At 0–95 ◦C, sucrose forms monoclinic anhy-drous crystals that have an axial ratio of 1.2532 :1 : 0.8895; 103◦ [30]. The crystallization en-thalpy is 360 J/mol, and the density is 1.5879g/cm3 at 15 ◦C and 1.5871 g/cm3 at 20 ◦C [31].
Sugar crystals of different morphology andshapes are formed, depending on the conditionsof crystallization and the nonsugars inserted inthe crystal lattice. Hence, commercially crystal-lized sugar occurs in many crystal forms [32].
The melting point of pure sucrose is 186 ◦C;commercially available sugar melts in the range175–190 ◦C, depending on purity.
On heating a sugar melt (5–20 min) to 180–210 ◦C, the disaccharide bond is cleaved andthe resulting monosaccharides eliminate wa-ter to yield volatile and nonvolatile aroma im-parting substances, such as 2-butanone [78-93-3], 2-acetofuran, furanone, 5-(hydroxymeth-yl)furfural [67-47-0], levoglucosan [498-07-7],
levoglucosone [37112-31-5], anhydroglucoses[498-07-7], difructose anhydrides [124277-48-1], and polymers of these monomers. The prod-uct is known as burnt sugar.
When heated above 250 ◦C, the carbon chainis increasingly broken up to yield small gaseousmolecules, such as CO2 and H2, the residue re-maining is sugar charcoal.
3.2. Physical Properties of AqueousSugar Solutions
When sucrose is dissolved in water, the threeprimary hydroxyl groups are hydrated first withthe formation of hydrogen bonds, followed bythe secondary hydroxyl groups. Up to a massconcentration of about 67% at 25 ◦C, sugarmolecules are hydrated with water molecules inthe form of clusters [33]. For this reason, sugaris readily soluble in water. The pH of sugar so-lutions is 5.0–8.0. The pK values at 25 ◦C arepK1 = 12.7 and pK2 = 13.1.
At higher concentration, sugar forms viscoussyrups that are easily supersaturated. Their rateof crystallization is influenced by the type andquantity of impurities present in the solution (seeFig. 8). The solubility of pure sucrose in wateras a function of temperature is given in Table 2
Sugar 7
[34]. The density of aqueous sucrose solutionsas a function of concentration and temperatureis listed in Table 3 [35]. Viscosity is importantfor the industrial processing of sucrose solutions(see Table 4) [36]. It increases with increas-ing concentration (η = A · 10 · Bb/100 − b) anddecreases with increasing temperature (η = A ·B/T, where A and B are constants, T is the abso-lute temperature, and b is the solids content).
The most important physical properties ofsugar and sugar solutions are summarized in[37].
3.3. Chemical Properties
As a result of the labile furan ring in the fruc-tose portion of the molecule, sucrose can becleaved easily into its components by hydrogenactivation or enzymes. This reaction proceedswith a gain in energy (− 27.9 kJ/mol). The dex-trorotatory labile β-fructofuranose released atfirst is rearranged quickly to give the levorota-tory tautomeric mixture (→ Fructose). This is afirst-order reaction. Thus, the resulting mixtureof equal parts of glucose and fructose becomeslevorotatory [α] 20
D =− 22.2◦ and is called invertsugar. The cleavage reaction is known as the in-version of sucrose.
Sucrose can be cleaved from both the fructo-sidic (β-fructosidases, invertase) and the gluco-sidic (α-glucosidases, sucrases) sides. Microor-ganisms are capable to produce both enzymes.Cleavage by β-fructosidases predominates inplants and cleavage by α-glucosidases in ani-mals. The latter also applies to the enzyme sys-tem of the human mucosa. Because sucrose, be-ing a disaccharide, cannot pass through the in-testinal wall, its enzymatic cleavage is a require-ment for the absorption and metabolism of su-crose.
In food production, the processing parame-ters (pH, temperature, residence time) are opti-mized so that the amount of invert sugar pro-duced is just enough for the flavor and browning(color).
With acidic food and drink, attention must bepaid to the fact that only traces of hydroxymeth-ylfurfural (HMF) are formed from the fructosepart of the molecule (→ Fructose, Chap. 2.3).
In the alkaline degradation of sugar duringjuice purification, the invert sugar present in
sugar beet is degraded to organic acids (d- andl-lactic acid, acetic acid, formic acid, and sac-charinic acid). Alternatively, juice purificationcan be carried out in such a way that the invertsugar is not broken down (cane sugar juice pu-rification).
3.4. Sensory Properties
The sweetness of aqueous sucrose solutions isset as the standard (= 1) and is used by way ofcomparison to determine the relative sweetnessof other substances. The intensity of sweetnessof food and beverages depends on sugar concen-tration, temperature, and the matrix of the food(viscosity in the case of solutions and texture inthe case of pasty, solid foods).
The taste profile of sugar is purely sweet andfree fromall secondary tastes.Aswith the sweet-ness, the course of the intensity–time curve ofsucrose solution, an important characteristic forthe sensation of sweetness, is used as the stan-dard for the determination of curves of this typefor other sweetening agents [38].
4. Sucrochemistry, Chemical andEnzymatic Synthesis
4.1. Sucrochemistry
Since the middle of the last century, the world’ssugar production has increased greatly (Chap.23, Table 17) and is consistently higher thanthe requirements of traditional markets. Further-more, the production of sugar could be increasedstill further; sugar is produced in a highly purestate and is one of the cheapest bulk organicchemicals. For all of these reasons, attemptshave been made since 1948 to use sugar as araw material for chemical syntheses.
With the oil crisis in the mid-1970s, theseefforts were given a strong impetus by the gen-eral realization of the limited availability of fos-sil fuels. Sugar presented itself as an easily re-newable energy resource (see also→ Fructose,Chap. 2.3). This area of sucrose chemistry wasgiven the name “sucrochemistry.” The numer-ous microbiological transformation products of
8 Sugar
sucrose are not included in the field of sucro-chemistry.
Processes for the use of sucrose [39] orother compounds, which are obtainable from theskeletal substances of beet and cane, as chemicalraw materials can be divided into three groups:1) Direct chemical conversion of the unchanged
sucrose molecule2) Chemical conversion of compounds made
from sugar (e.g., glucose, fructose, iso-maltulose, leucrose, isomalt, hydroxymeth-ylfurfural)
3) Use of side products of sugar processing forthe production of bulk chemicals, e.g., xy-lose or furfural (→ Furfural and Derivatives,Chap. 3) frombagasse, l-araban, l-arabinose,and pectin from beet cossettesExtracted beet cossettes are used as sub-
strates in solid fermentation to produce protein-enriched cossettes [protein content 19–24% ofdry substance (DS)] [40], and enzymes, such aspectinases and other hydrolases [41].
Apart from esters with fatty acids (e.g., forthe production of biologically degradable sur-factants and ethers), sugars or products belong-ing to the second group are oxidized to carbox-ylic acids, reduced to alcohols, or subjected todestructive hydrogenation and reductive amina-tion.
In summary, sucrochemistry has not gainedmuch success until now although it in-cludes interesting compounds, e.g., 4,1′,6′-tri-chloro-4,1′,6′-trideoxygalactosucrose [56038-13-2], which is suitable as an intense sweetener.
4.2. Chemical and Enzymatic Synthesis
Despite its great economic importance, attemptsto synthesize sucrose were made relatively late.In 1928, the tetraacetates of glucopyranose andfructofuranose with free glycosidic groups werechemically linked by the addition of dehydratingagents [42]. However, the resulting octaacetatesdid not have the proper steric conformation ofsucrose (α-1→ β-2) but were the acetates ofthe isomeric isosucrose [43].
The first successful chemical synthesis of su-crose involved the condensation of 1,2-anhydro-3,4,6-tri-O-acetyl-d-glucopyranose (Brigl’s an-hydride) with syrupy 1,3,4,6-tetra-O-acetyl-d-fructofuranose, followed by deacylation. The
synthesis could be improved by using crystal-lized 1,3,4,6-tetra-O-benzyl-d-fructofuranose(instead of the syrupy tetra-O-acetyl com-pound), but here too the yield of sucrose wasonly ca. 35% [44].
A successful biochemical synthesis [45] useda bacterial phosphorylase (EC 2.4.1.7), whichcatalyzed the following reaction:α-d-glucose 1-phosphate + d-fructose �
sucrose + phosphateIn this way, sucrose could be prepared in
the crystalline state [46]. However, the reactionequilibrium favors cleavage, reflecting the phys-iological significance of sucrose phosphorylase(degradation reaction).
4.3. Plant Biosynthesis
In plants, the biosynthesis of sucrose occursin the cytosol (especially of the leaves) fromthe “active” forms of glucose and fructose: uri-dine diphosphate (UDP) glucose and fructose6-phosphate. These two compounds are, in turn,formed from the triose phosphates produced di-rectly in the Calvin cycle [47]:
With the cleavage of the pyrophosphate (PP)formed in reaction 1, three energy-rich phos-phate bonds are hydrolyzed in the synthesis ofsucrose. Hence, the equilibrium favors forma-tion of sucrose.
Sugar 9
At the time of storage, sucrose is transportedin an energy-dependent process from the epigealparts of the plant (source) through the phloemand into the roots [48]. The storage parenchymalcells (sink), in turn, concentrate sucrose withinthe tonoplasts in an energy-dependent process.Thus, the source–sink relationship and the os-motic conditions are retained [18, 49].
The assimilation efficiency in sugarcane wasstudied with labeled 14CO2. C. E. Hartt [50]found that 65% of the carbon dioxide absorbedis used for the synthesis of sucrose and that asingle leaf of about 5.7 dm2 produces 100 mgof sucrose in 1 h. Of these 100 mg, 74 mg istransported to the stalk for storage. A large plantpossesses about 22 leaveswith a total area of 122dm2, which corresponds to a sucrose productionof 2.140 g/h.
5. Methods of Analysis
In the analytical methods applied in the sugarfactory, a distinction is made between methodsfor
1) Final product control, which are largely stip-ulated in international agreements (WHO–FAO Codex Commission, pharmacopoeias,etc.) and in national food and feed regulations.
2) In-process control, which must be simple buteasily reproducible because of the large num-ber of analyses to be performed. For this pur-pose, optical methods, polarimetry, and re-fractometry have gained acceptance.
At first, quartz wedge compensation instru-ments were used exclusively as polarimeters.They were calibrated to give a rotation of 100(100◦ Ventzke), corresponding to 34.657 radi-ans, for a solution of 26.00 g of pure sucrose,weighed in air, made up to 100 cm3 with wa-ter, and measured with sodium light (D lines)at 20 ◦C in a 2-dm tube. The instruments werechecked with calibrated quartz plates becausequartz and sucrose have about the same rotatorydispersion at wavelengths close to the D lines.With 26 g of substance per 100 cm3, the percent-age of sucrose in the sugar solution is obtaineddirectly from the angle of rotation in degreesVentzke. Later 100◦ S (International Sugar De-grees) was used, corresponding to 34.616 radi-ans for the yellow sodium lines of 589.44 nm
[51]. Lead acetate solutions were used to clarifythe solution. For environmental reasons, clari-fication is achieved today with aluminum–zincsalts with sodium or calcium hydroxide solu-tions. As a further alternative to lead acetate clar-ification, polarimeters are being used that workin the near-infrared range, to permit a measure-ment of unclarified, dark solutions directly afterdilution.
More recent measurements with highly puri-fied sucrose showed certain deviations from theold scale. Thus, the hundred-degree points forvarious wavelengths were redetermined so thatfurther development of instrumentation wouldnot be hindered [52]. The hundred-degree pointfor the mercury isotope line 198Hg is:
α20.00◦C
546.2271 nm= 40.777◦±0.001◦
for the yellow sodium lines:
α20.00◦C
589.4400 nm= 34.626◦±0.001◦
for the helium–neon laser:
α20.00◦C
632.9914 nm= 29.751◦±0.001◦
for near-infrared wavelengths:
α20.00◦C882.60 nm = 14.836◦±0.001◦
α20.00◦C880.00 nm = 14.927◦±0.001◦
and is defined as 100◦Z in the sugar polarimeter.Another important method is determination
of the solids content of juices, syrups, and crystalmagmas (massecuite). In the beet sugar indus-try this is determined almost exclusively fromthe refractive index of the solutions. The refrac-tive indices of pure sucrose solutions have beendetermined with great accuracy and are interna-tionally defined [53].
Errors made in using the refractive index fordetermination of the solids content of impuresugar solutions increase as the nonsugar por-tion increases. For molasses, these errors are ofthe order of 1–3% absolute, compared to val-ues obtained by determining the water contentof molasses with Karl Fischer reagent solutions(→ Gas Production, Chap. 8.2.2.3). Neverthe-less, the accuracy of the refractometric methodis sufficient for technical purposes.
10 Sugar
The degree of purity p (or simply purity) isan important value in controlling the success oftechnological measures. Determined from thepolarization, p gives the sucrose content as apercentage of the total solids content. In the rawjuice obtained by extracting sugar beet, sucroseaccounts for about 90% of the solids content(i.e., the purity of raw juice is 90%); the purityof thick juices is approximately 92% and that ofmolasses ca. 60%. This type of purity determi-nation gives approximately correct results onlyin the case of intermediates in sugar beet pro-cessing. It cannot be applied to cane products be-cause the polarimetric determination of sucrosegives incorrect results owing to the high contentof invert sugar in these products. In these cases,modern analytical methods for saccharides (GC,HPLC, ion chromatography)must be used to de-termine the actual sucrose concentration in theproducts.
In themaking of sugar, other important meth-ods of analysis involve the determination ofcolor, inorganic constituents (ash), and individ-ual nonsucrose organics, e.g., glucose and fruc-tose (invert sugar), raffinose, d- and l-lacticacid, citric acid, amino acids, betaine. Lately,enzymatic and chromatographic methods [GC,high-performance ion-exchange chromatogra-phy (HPIC), HPLC, high-performance anion-exchange chromatography (HPAEC)] for the de-termination of organic nonsugar substances havegained acceptance.
The International Commission for Uni-form Methods of Sugar Analysis (ICUMSAhttp://www.icumsa.org), founded in 1897,meetsonce every four years (since 2002 biennially)to solve analytical problems on an internationallevel. The results of thesemeetings are publishedin the Commission’s proceedings (last issues:1990, 1994, 1998, 2002, 2004). Methods for theanalytical control of final and intermediate prod-ucts that are accepted by ICUMSA were sum-marized in monographs in the past [54] and arepublished in the loose-leaf ICUMSA MethodsBook today [55].
In addition to laboratory methods, on-linemeasurements of, e.g., dry substance (measuredby refraction), white sugar color, pulp moisture,juice alkalinity, and juice hardness are gainingin importance.
The sugar beet, Beta vulgaris altissima, is abiennial plant that is, however, harvested afterthe first vegetation period for the production ofsugar. At that time, the largest amount of sugaris stored in the fleshy root. Thus, the sugar beetis processed before it reaches physiological ma-turity.
The sugar beet grown today was bred byAchard from the “white Silesian beet” bymeansof selection. The wild beet Beta maritima L.,still found in the coastal areas of the Mediter-ranean and the Atlantic, is regarded as the orig-inal form of sugar beet. Like other plants be-longing to this genus (fodder beet, beetroot, andchard), the sugar beet has 2×9 chromosomes(i.e., it is diploid).
Classical breeding was based on individualselection, in which the quality of the motherplant was judged on the basis of the propertiesof the progeny (surface appearance, density ofroots, sugar content of cell sap, etc.). The devel-opment of a new variety took 16–20 years. Newbreeds were largely impaired because of self-sterility and the resulting difficulty in inbreed-ing. A considerable step forward was achievedaround 1950 with the introduction of hybridbreeding by the use of sterile male plants. Thus,inbred lines could be developed and crossed. In-troduction of the haploid technique has madebreeding easier. In this technique, plants are re-generated from unfertilized germ cells. Theseplants are 100% homozygous after the doublingof their set of chromosomes. Consequently, inthe breeding of sugar beet, improvements inquality can now be achieved much faster. Withthe help of genetic engineering [57], efforts havebeen made to make sugar beets resistant to vi-ral diseases (e.g. Rhizomania A, B, and P types,caused by the virus BNYVV and transmitted bythe fungus Polymyxa betae) and to herbicides,as well as to changes in the concentration ofsugar or other constituents (raffinose, betaine,etc.). From the 1970s to 2000 breeding of Rhizo-mania resistent varieties with normal sugar yieldwas a very important goal and the success wasa milestone in sugar beet breeding. Concepts to
Sugar 11
develop Rhizoctonia solani resistance in a sim-ilar way are just at the beginning, and the firstresistant variety was registered in 2001 [58].
Genetically monogerminal seeds are usuallysown in pellet form. Fungicides and insecticidesare contained in the cover mass so that furtherplant protection measures, with the exceptionof herbicide treatment, are not required duringgrowth.
Efforts are made to achieve a plant popula-tion of 80 000–120 000/ha, depending on cli-matic conditions (row width is 38–50 cm; spacebetween plants in a row is 18–22 cm in the caseof cultivation without thinning and 12 cm in thecase of mechanical thinning to give a desirednumber of plants per hectare after germinationof the seeds). With the introduction of geneti-cally monogerminal seeds, the labor expended(working hours) in sowing sugar beet was re-duced from about 45 h (cultivation with thin-ning) to 3–11 h for cultivation without thinning,depending on the size of the field (0.5–5 ha). Thetotal amount of labor (including preparation ofthe field, harvesting, and loading of the beets)decreased to the same extent. In fact, the work-ing hours per hectare were reduced from 260 hin 1967 to 15–50 h, depending on the size of thefields and the harvesting technique used (e.g., asix-row self-propelled combine harvester). Theharvesting process, subsequent mechanical re-moval of dirt tare, and the loading of beets mustbe conducted gently so that mechanical damageto the beets is as low as possible (< 600 cm2 per100 beets). With mechanically damaged beets,high sugar losses occur during storage, washing,and fluming. For undamaged beets sugar lossesat this stage are typically 0.3–0.5%, but for dam-aged beets ca. 1%.
In Central Europe and the United States, thevegetationperiod is about 170–200 days (April 1to October 15). The time required between sow-ing and germination is 22 days. In the case of awinter rainfall of 240 mm, the amount of precip-itation during the vegetation period should be atleast 360 mm. The total heat (sum of the averagedaytime temperatures during the vegetation pe-riod) required to ripen sugar beet is 2500–2900,with the longest possible duration of sunshine inthe months of July to September.
The nutrient withdrawal per hectare for 10t of beets including the leaves is 45 kg of ni-trogen, 6 kg of phosphorus, 52 kg of potassium,
15 kg of sodium, 16 kg of calcium, and 8 kg ofmagnesium. Depending on the fertilization stateof the soil (→ Fertilizers, Chap. 2.3.2), fertiliza-tion with 120–160 kg of nitrogen, 80–130 kg ofP2O5, and 150–250 kg of K2O per hectare com-pensates for deficiencies. In organic fertilizationwith farmyard manure, liquid manure, or straw,the mineral components present should also betaken into account. For fertilization, the ratioof N : P : K must be about 1 : 0.4 : 1, based onthe pure nutrients, to make sure that the planthas a balanced supply of nutrients. Since thelate 1980s, the beet yield (return) per hectarein Western Europe has been an average of 50.8t, with large regional variations (e.g., Finland29.2 t/ha, Switzerland 60.3 t/ha). The yield inthe United States is somewhat lower, and that inthe Commonwealth of Independent States andother Eastern European countries is only two-thirds of this amount.
Since the sugar concentration in beet doesnot vary greatly (18.4% in Austria, 13.9% inGreece), the mass of white sugar produced perhectare correlateswith the beet yield per hectare.This is ca. 7.47 t/ha in Western Europe (Fin-land 4.20, Switzerland 9.06), 6.5 t in the UnitedStates, and 4 t/ha in Eastern European countries.
Together with the tops (yield of ca. 20–40t/ha), which constitute a valuable feed aftersilage, the utilizable energy obtained per hectareof a sugar beet field is 219 GJ (100%), com-pared with 89 GJ/ha for the cultivation of pota-toes (40%), 69 GJ/ha for wheat (31%), and 114GJ/ha for the cultivation of grain corn (52%).
In most areas under cultivation, sugar beet iscut back when harvested. In Europe, for exam-ple, the leaves and the beet crown (ca. 15%of themass of the defoliated root) are separated fromthe root body. In the United States, the crownpart that is cut off is much smaller (≈ 6%). De-spite the use of considerable mechanization insowing, care, and harvesting, and of herbicides,fungicides, and insecticides, the cultivation ofsugar beet is still one of the most labor intensiveareas in agriculture.
6.2. Chemical Composition and BeetQuality
Even beets that are harvested from the same fielddo not represent homogeneous material. There-
12 Sugar
Figure 2. Average chemical composition of sugar beet
fore, data on the chemical composition of sugarbeets (Fig. 2) should always be regarded as aver-age values for normally grown beets. Also, cer-tain criteria must be maintained as far as sam-pling and the size of random samples are con-cerned [59].
The root body consists of about 75–78%wa-ter. Of its solids (22–25%), sugar (sucrose) ac-counts for 15–18%, raw protein 1–1.2% (totalN×6.25), raw fat 0.1%, raw fiber 1.1–1.3%,pectinous substances 1.0–1.2%, nitrogen-freeextractive substances (apart from sucrose) 2.8–3.0%, and inorganic components 0.7–0.9%.Similar figures were given in a monograph in1998 [1]. In sugar technology, sugar beets aresubdivided more usefully into “marc” and “celljuice.” The marc, which accounts for ca. 4–5.5% of the sugar beet mass, refers to the com-ponents that are insoluble in water under cer-tain extraction conditions (i.e., beet skeletal sub-stances consisting of cellulose, lignin, pectin,araban, and galactan). The cell juice contains,in addition to sucrose, other soluble nonsucrosesubstances, or nonsugar substances, includinginvert sugar (0.1–0.2%), raffinose (→ Carbo-hydrates, Chap. 2) (0.05–0.2%), and kestoses(trisaccharides consisting of one molecule ofd-fructose and one molecule of sucrose; i.e.,fructosylsucroses); a soluble pectin–protein–hemicellulose complex; organic acids (oxalic,
citric, tartaric, malic, etc.); proteins, polypep-tides, glutamine, glutamic acid, asparagine, andother amino acids; betaine and other plant bases;nucleotides; saponins; enzymes; vitamins; theinorganic components potassium, sodium, cal-cium, andmagnesium as cations; and phosphate,chloride, sulfate, and nitrate as the main inor-ganic anions.
Of the soluble nonsugar substances in sugarbeet, 30–40 wt% is eliminated during purifica-tion of the juice (with Ca2+-precipitable anions,pectins, proteins, Mg2+); the remainder is leftin the juice and prevents complete crystalliza-tion of the sugar, leaving a final syrup, molasses.In molasses, for 1 part of nonsugar substances,about 1.5 parts of sugar are present in the dis-solved state. The loss of sugar in molasses isthe largest single loss (i.e., 12–18% of the sugarcontent of the beet).
For this reason, efforts are being made to pre-determine the expected loss of sugar inmolassesand /or the purity of the thick juice,which closelycorrelate with each other, from beet constituentsthat can easily be determined analytically (con-tent of sugar, K+, Na+, α-amino-N, and invertsugar). The average values of these constituents,also called quality parameters, vary greatly fromyear to year, even in a limited area under culti-vation (e.g., southern Germany). Thus, the con-tent of potassium is 45–60 mmol/kg of beets, of
Sugar 13
sodium 5–10 mmol/kg, and of α-amino-N 15–32 mmol/kg. Scientific papers of different au-thors concerning these quality parameters weresummarized and compared in 1996 [60].
In controlled cultivation experiments, theability to influence some quality characteristicswas determined analytically [61]. The main in-fluencing factors were found to be location andweather (Table 5). The statement that the influ-ence of the variety is, at ca. 8%, relatively lowapplies only when approved, time-tested vari-eties are compared with each other. The differ-entiation between varieties that are “good” andthose that are “unsuitable” for a certain area un-der cultivation is considerably greater.
Apart from these chemical characteristics,the mechanical properties of the root, such asbreaking and bending strength, elasticity, andcutting resistance, are of prime technologicalimportance. Consequently, they are also signifi-cant for the economic success of beet sugar pro-duction.
6.3. Preparation
After harvesting, sugar beets are stable for only alimited time and should be processed as quicklyas possible. For this reason, beet sugar factoriesoperate for only part of the year (campaign), e.g.,about 80–120 days (from the end of Septemberto the end of January) in Central or NorthernEurope and the United States. In more southerncountries (e.g., Greece and Italy), work starts inJuly/August. About 2000–25 000 t of beets areprocessed per day, depending on the capacity ofthe factory. For economic reasons, most facto-ries produce sugar for consumption immediately(white sugar factories). Only a few factories con-tinue to produce raw sugar first, which is thenprocessed into white sugar in refineries or otherwhite sugar factories.
6.4. Delivery and Storage
For practical reasons, even larger fields must beharvested at one time. The harvested beets areeither stored temporarily in clamps at the sideof the field or transported directly to the fac-tory. Before the transport vehicles are loaded,
the beets are mechanically precleaned to reducethe dirt tare from ≈15% at harvest to < 10%.
Mechanized harvesting has the disadvantageof delivering the beets along with leaf rem-nants, stones, and a lot of soil, especially in wetweather. This can lead to tremendous problemsduring processing (fluming, washing, cutting) inthe factory. In the annual processing of 500 000t of beets, an average of 60 000 t of soil accu-mulates (40 000 m3).
If the separated soil cannot be reused – af-ter being stored temporarily to restructure itsmechanical properties – the profitability of sugarproduction is questionable because of the highcosts of its disposal in industrialized countries.
Depending on long-term weather conditions,harvesting must be completed before the rainyseason (e.g., in Italy) or frost (e.g., in Finland orMontana, United States) and long before the endof the working period. Therefore, a part of theharvest must be kept temporarily in field clampsor large piles on natural or paved ground.
Tokeep the loss of sugar during storage as lowas possible, only ripe, healthy, low-damaged,and clean beets should be stored for longer pe-riods. Sugar losses occur through respiration,since the sugar beet requires a certain amountof energy to maintain its vital functions, andthrough aerobic degradation or rot caused byyeasts, molds, and bacteria. Excessive mechani-cal damaging and bruising of beet causes highersugar losses during storage, due to increasedmi-crobiological attack at the damaged surface andadditional sucrose utilization of damaged beet toheal the injury. The optimal storage conditionsfor sugar beet are obtained when beets are piledin a uniformly porous manner: that is at no pointin the pile should the hollow spaces betweenbeets be able to get clogged with dirt, weeds, orbroken pieces of beet. The porosity of the sugarbeet pile should permit the heat generated byrespiration, ca. 3000 kJ/t of beets per day, to bedissipated by natural ventilation easily and thetemperature of the entire pile to be kept at + 2to +4 ◦C. If necessary this low temperature canbe maintained by forced air ventilation at nightwhen the air is cooler. In addition, a porous sugarbeet pile permits the relative humidity to be keptconstant (ca. 85–95%) so that the beets do notwither excessively (water loss) [62].
Until now, only unwashed sugar beets werebelieved suitable for storage. However, the opti-
14 Sugar
Table 5. Influence of different factors on yield and composition of sugar beets, in percent
mal conditions for storage described above areachieved more easily if sugar beets are washedand then piled to a height up to 10 m. The mois-ture remaining on the beet surface can be re-moved by forced air ventilation, which in ad-dition has the advantage of faster temperaturereduction in the pile as a result of water evapo-ration [63].
Despite all preventive measures, sugar lossesduring storage cannot be avoided completely.Depending on the temperature in the sugar beetpile (+ 2 to + 10 ◦C), the losses are 150–200 gof sucrose per day per tonne of beets (0.015–0.020% per day, beet based).
Frozen beets can be stored for long peri-ods with only minor sugar losses [64]. How-ever, they must be processed quickly after thaw-ing because they rot easily. In the northern re-gions of the United States, to prevent thawing,beets are stored in free span insulated buildingswhere they freeze. The frozenbeets are protectedagainst sudden warm spells.
6.5. Thick-Juice Storage
The recommendations made until now forachieving a year round working period in sugarfactories by preserving the beets (freezing, dry-ing, etc.) have not gained acceptance because oftheir high costs.
Since the mid-1960s, the working period insome factories (e.g., in theUnitedStates, France,and Germany) has been extended by making thebeet processing factory (parts of the plant pre-ceding the sugarhouse), including the evaporat-ing station, larger than the sugarhouse and bytemporarily storing the thick juice in floating-roof tanks [65] with a capacity of up to 100 000m3. In tanks without floating roof, which areavailable at lower investment costs, the juice sur-face must be protected against yeasts by paraf-fin, formalin, or caustic soda solution [66]. With
properly adjusted storage conditions in the bulk(DS content ≈ 67%, pH ≥ 9.0, temperature< 15 ◦C, lowest possible microorganisms con-tent), the thick juice can be stored for years with-out appreciable quality losses [67], but some-times thick juice degradation was observed [68].The profitability of this processing mode de-pends greatly on local conditions (costs for en-ergy, labor and investment) [69].
6.6. Weighing and Sampling
After the first weighing (gross − tare = netmass), one representative sample is taken, usu-ally mechanically and at random, from every de-livery. This sample is used for the determinationof dirt tare and partly for top tare [70], sugarcontent, and for the evaluation of quality. In thecase of dry unloading with a wagon or trucktipper, beets are conveyed via a dirt separator(roller grate, wire rod screen) to stacks arrangedon paved areas. In wet unloading according tothe “Elfa” process, beets are washed out of thevehicle or wagon and pass through flumes to thewashing stage.
6.7. Internal Transport, Washing
The beets are transported from the Elfa unload-ing areas or beet stacks to the actual washingstage in “flumes,” concrete or tiled channels laidin the ground about 0.5–1.2 m wide with a slopeof 1–2%. The beets are transported by means ofwater and simultaneously freed from a large partof the beet tare. Flume channels made of steelsheet are also installed above ground. Trash sep-arators in the channels intercept leaves, straw,and weeds (a type of mechanically operated ro-tating rake with free-swinging long prongs issuspended from the top of the channel), and a
Sugar 15
Figure 3. Cross section of a Maguin drum slicer [75]a) Slicing disk casing; b) Outer casing; c) Beet feed hopper; d) Hinge plate; e) Fixed disk; f ) Guide plate; g) Locking bar;h) Access for knife-box changing; i) Flap; j) Inspection hole; k) Blow-out connector (patented)
rock catcher removes stones (the beet flow isled over an ascending water stream whose flowrate is such that the beets remain afloat and thestones sink). The beets are lifted from the flumechannel to the level of the washing facility bywheels, screws, or inclined scrapers. Alterna-tively, the entire beet–water mixture is pumpedup bymammoth pumps or one- channel centrifu-gal pumps (unfavorable because heavy damageis caused to the beets). Before the beets enter thewashing facility, flume water is separated fromthe beet–water mixture with the help of square-roll screens or vibrating screens because part ofthe beet tare has already been separated from thebeets and is contained in the flume water.
The dirt still adhering to the beets is subse-quently removed in the washing facility. Thebeets are washed in trough washers, drums,washers with rotating agitating arms, or on vi-brating screens. Agitating washers consist oflong troughs that are divided into individualcompartments and provided with cylindricalscreens and a horizontal shaft. This shaft isequipped with stirring arms, transport arms, andthrowers. At the bottom, the washers have stonecatching compartments and hatches to allow pe-riodic withdrawal of wastewater. The beets arerubbed together, and thus washed, by the move-ment of the stirring arms.
In vibrating washers, the beets are trans-ported over a wedge-wire screen, which is madeto vibrate by a circular or linear vibrator. At thesame time, water at a pressure of up to 1 MPa issprayed on the rotating beets from the top. Since
the root canals of the beets are also touched bythe water jet, the beets obtained when vibratingwashers are used for the second wash are gen-erally cleaner than those obtained after only onewashing process.
Thewater requirement is as follows: for flum-ing, ca. 500–800%, beet based; for washing,150–200%, beet based; and for the operationof a single stone catcher, 70–100%, beet based.The sugar losses during fluming andwashing are0.05–0.5%, beet based, depending on the extentof damage to the beets. Losses of < 0.2% weregiven as standard for technological leadership[71].
6.8. Processing Wash and Flume Water
The flume and wash water contain beet parti-cles. For this reason, all of the wastewater mustfirst pass through separators. These are mechan-ical screening devices with round or slit perfo-rations (0.6–4 mm) that remove beet and leaffragments and root hairs from the water. Theintercepted material is separated into its compo-nents in cyclone washers. Larger beet particles(> 2 cm) and tails are returned to the washedbeets. Smaller particles are either led to the pulpdryer or used directly as feed.
The drained flume and wash water is ledto wastewater treatment plants for mechanicalpurification (sedimentation). The thickened soilsludge, which contains most of the beet soil,is pumped into settling tanks equipped withdrainage systems for dewatering and restructur-
16 Sugar
ing soil. After two to three years, the soil is com-pact enough to be reused.
Attempts to remove the beet soil from thethickened sludge directly by means of sedimen-tation centrifuges did not give the expected re-sults [72].
The mechanically clarified water is reusedfor fluming and washing (flume and wash watercycle). In this way, only 25–30% (beet based)of industrial water (condensate) need be addedto the water cycle as make-up during the lastrinsing of the beets after washing. This quantitycorresponds to the amount of water pumped offwith the thickened soil sludge. To prevent ex-cessive bacterial growth in the circulating flumeand wash water, the addition of Ca(OH)2 to thewater to give a pH of 10–12 is appropriate. Atthe same time, the sedimentation of solid matterin the mechanical settling tank is improved.
Since the transport water pumped off withthe soil sludge has a high organic contamination(COD5000–10 000 mg/L), it is first subjected toanaerobic degradation with an efficiency of 90–95%. The wastewater is subsequently subjectedto aerobic treatment, and nitrification or denitri-fication, depending on the demands made on thecomposition of the wastewater to be discharged(e.g., total N content) [73].
Ammonium ions enter the wastewaterthrough the vapor condensates of the evaporatorstation, which have a NH4–N content of 100–200 mg/L, depending on the glutamine contentof the beets. For this reason, ammonia can beeliminated from the condensates by air stripping[74].
Since the beets (water content≈ 75%) carrysufficient water into the production process,which accumulates as condensate, a factory to-day can largely do without ground or surfacewater. The total COD burden on the wastewa-ter of a beet sugar factory is 2–3 kg per tonneof beets, with < 1 kg attributed to leadershiptechnology [71], and in the case of cane sugarfactories, 14–25 kg per tonne of cane.
6.9. Slicing Beets
From the washing facility, the beets, beet frag-ments, and beet tails are transported by belts orbucket elevators to the slicer hopper, which isinstalled above the slicers. As far as possible,
this bin should accept the amount of beets pro-cessed in an hour and should always be kept full(controlled via load cells) to guarantee uniformfeeding of the slicers. The beets are weighedeither before the slicer hopper (with a tippingweigher) or after slicing (with a conveyer scale).The weight of the “clean beets” obtained in thismanner is used to calculate internal yield.
Besides, vertical shaft slicers with horizontalcutting disks, rotary drum slicers are being usedincreasingly for the slicing of beets. The outputof slicers is controlled by altering their speed,and the set output required is controlled by theconveyer scale in the path of the cossettes to theextraction system. This scale sends out the im-pulse for output control. A constant supply ofbeet cossettes is required for good extraction,along with a constant mass flow in the followingprocess steps.
A typical rotary drum slicer is shown in Fig-ure 3 [75]. The beets enter the slicing drum viaa feed hopper. As a result of the comma-shapedbaffles, the rotating motion of the slicing drum(20–120 rpm), and the resulting pressure of thebeet mass, the beets are cut by knives screwedinto the knife boxes. Three knives, with a lengthof 200 mm each, are mounted side by side in aknife box,resulting in a cutting length of 600mm.
If a foreign body appears (stones, metalpieces, etc.), the stone catcher door springs openand themachine automatically comes to a stand-still. Drum slicers are built with an output of upto 5000 t/d.
The zigzag Konigsfelder knives are usedmost often today (Fig. 4). These knives shouldtheoretically produce cossettes having a V-shaped cross section. Cossettes of 3–5-mmthickness result in surfaces of 2.5–3.5 m2 perkilogram cossette, a cossette circumference of25–30 mm, and a cross-sectional area of 15–35mm2.
Figure 4. Konigsfelder knife
Sugar 17
For evaluation of the quality of beet cossettes,two criteria have been introduced:
1) The Silin number gives the length in metersof 100 g of beet cossettes arranged in a row.Well- cut slices give a length of 10 to 16, de-pending on the spacing of the knives.
2) The “Swedish number” is the quotient“weight of cossettes≥ 5 cm”/“weight of cos-settes ≤ 1 cm” and has a value of 15–25 forgood cossettes.
The mechanical strength (elasticity) of sugarbeets has a great influence on cossette quality[76]. The preferred quality, which is slightly de-pendent on the type of extraction, are small, brit-tle cossettes.
7. Production of Juice (Extraction)
The extraction of beet cossettes is an importantprocess step that greatly influences sugar lossesand subsequent process steps. Upon extractionunder sterile conditions with as little water aspossible, extensive desugarization of the beetcossettes should be achieved and a raw juice ofhigh purity and density (solids content) shouldbe obtained.
7.1. Principles [77]
The sugar dissolved in cell juice can pass outof the beet cossettes (solid phase) into the ex-traction liquid only if the cell and vacuole mem-branes are either opened mechanically (e.g., byproducing a finely ground pulp) or denaturedthermally. When beets are cut, about 5–15% ofthe cells are damaged mechanically to such anextent that an exchange can occur between thecell components, including those dissolved col-loidally, and the extraction liquid. The remainingintact cells must be opened irreversibly by theaction of heat. Denaturation of the cells shouldoccur quickly (i.e., at the highest possible tem-perature) [78]. At 80 ◦C, 80% of all the beetcells are opened in 5 min; at 70 ◦C, about 14min is required to achieve the same result. Thetransfer of sucrose and other water-soluble non-sugar substances from the denatured cossettes tothe extraction liquid occurs in two phases:
1) Transport from the inside of the cossettes tothe surface
2) Transport from the surface of the cossettes tothe extraction liquid through the entire dis-tance of extraction
Since this is a disperse system, Fick’s secondlaw applies to themass transport. However,masstransport is calculated more easily according toFick’s first law.
If ds is the amount of substance that diffusesin time dt through the surface F of the cossetteat a concentration difference dc along the pathdr, then
.m=
dsdt
= D·F ·dcdr
The diffusion coefficient D for beet tissue is≈1×10−5 cm2/min at 70 ◦C. According to theEinstein relation, the diffusion coefficient is tem-perature dependent. Consequently, the formulasgive the dependence of practical juice extrac-tion on temperature, cossette shape (surface),amount of extraction liquid (concentration gra-dient), and extraction time.
According to the formula, the extraction tem-perature should be as high as possible to ac-celerate mass transport. This can be fulfilledonly within certain limits. Temperatures that aretoo high lead to impure, poorly processible rawjuices because structural substances of the cellwalls ( pectin–araban–protein complex) are alsodegraded to a considerable extent and thus be-come water soluble. The following temperaturecourse represents a compromise: the cossettesare heated to 70–78 ◦C for a short time (about 5min) to denature the beet cells, and extraction iscarried out at 69–73 ◦C. Optimal temperaturesdepend on the growth conditions of the beet (i.e.,they vary from year to year) and on the equip-ment. They must be determined in practical op-eration.
The temperature in the extraction system alsoinfluences the vital functions of microorgan-isms. Soil bacteria, especially mesophilic bac-teria, enter the extraction system with the soilstill adhering to the washed beets (0.1–0.5%).Possibly, other strains of bacteria enter the sys-tem via the extraction water. As a result of theirmetabolism, these bacteria cause sugar losses (apart of the “unaccounted losses”) that, in the caseof larger infections, can amount to 0.1–0.2% ofsugar (beet based). The turnover of mesophilic
18 Sugar
bacteria can be limited by avoiding longer spellsat the temperatures at which they grow best (<40 ◦C) or even by killing them through expo-sure to higher temperatures. In contrast, ther-mophilic organisms (e.g., Bacillus stearother-mophilus, Clostridium thermohydrosulfuricum,now named Thermoanaerobacter thermohydro-sulfuricus [79]) are not inhibited by the tempera-tures allowed for extraction. For this reason, reg-ular treatment of the extraction system with dis-infectants (→ Biocides, Chap. 2.6,→ Biocides,Chap. 2.8) (e.g., hydrogen peroxide, glutaralde-hyde, peracetic acid, and especially 30 or 40%formalin) cannot be avoided. A quantity of for-malin equal to 0.5–1.0% of the hourly raw juicevolumetric flow rate (i.e., 50–100 kg per 100 m3
of raw juice per hour) should be added suddenly.The interval between two additions depends onthe intensity of the infection. In general, shockdisinfection must be conducted every 8–24 h.Today, after the introduction of hops β-acids(BetaStab 10A), rosin acids, and myristic acidas antibacterials for beet extraction, it is possi-ble to avoid addition of strong disinfectants, butat higher costs [80]. Enzymatic determinationof the concentrations of l- and d-lactic acid hasproved useful in monitoring the microbial state[81]. l-Lactic acid is the main acid formed mi-crobially in the extraction system. Other carbox-ylic acids (acetic, propionic, and butyric acids),as well as ethanol, acetone, nitrite, hydrosulfide,and hydrogen can also be formed [79, 82]. Fur-thermore, pH measurements in the extractionsystem can be used to detect infection.
The demand for cossettes with a large sur-face area can be fulfilled to only a certain ex-tent; otherwise, the permeability of the cossettespacket with regard to the juice is not guaran-teed. This applies especially to equipment with-out forced charging. The charging of the extrac-tion equipment, which is expressed as kilogramsof fresh cossettes per hectoliter of extraction vol-ume, should be as high as possible to achieve ahigh relative velocity between the cossette massand the extraction liquid. In equipment with-out cossette-forced charging, a filling of 65–75 kg/hL can be achieved. A filling of up to55 kg/hL is possible in extraction systems withforced charging of cossettes. Calculation of thevelocity of the extraction liquid (the juice or op-erating velocity) is greatly simplified as follows:
w =S
qf=
S
q(1− Fs
d·100)
where w is the flow rate in meters per minute, Sis the amount of raw juice in cubic meters perminute, qf is the free cross section in square me-ters, q is the cross section of the extraction equip-ment in square meters, Fs is the cossette fillingin kilograms per hectoliter, and d is the relativedensity of the cossettes [83]. Therefore, the ve-locity depends on the “raw juice draft” (i.e., themass of raw juice that goes into the factory) andis expressed in weight percent (beet based). Forthermal reasons, efforts are made to attain thelowest possible raw juice draft (i.e., weight ofjuice/weight of beet); it is normally 105–115%(beet based).
Furthermore, the raw juice draft influencessugar losses during extraction. The losses areexpressed as the sugar remaining in the desug-arized cossettes, based on the beet mass pro-cessed. These “determinable extraction losses”are 0.12–0.28% (beet based) in continuousplants with a juice draft of 105–115% (beetbased). This corresponds to an extraction effi-ciency for sugar of 0.97–0.99. Extraction lossis reduced by about 0.01% (beet based) by in-creasing the draft by 1% (beet based) in eachcase.
Parallel to a sucrose extraction of 97–99%,approximately 20–30% of the total nonsugarsare extracted (i.e., about 70–75% remain in theextracted cossettes). Thus, the purity of the rawjuice is 89–91%, compared to 68–72% in thebeets. Of the nonsugar substances in the beet,about 42% of the total nitrogen, 88% of theprotein nitrogen, 72% of the calcium ions, 34%of the magnesium ions, and 17% of the alkaliions remain in the pressed pulp. The alkaline-earth and alkali ions in the pressed pulp are, forthe most part, present as pectates and pectinates[concentration ca. 70 milliequivalents (meq) per100 g solids of pressed pulp]. Thus, the degreeof extraction for cations is influenced decisivelyby that of the pectic substances. About 95% ofthe pectins introduced with the beets normallyremain in the desugarized cossettes. About 95%of the low molecular mass water-soluble anionsin beet are extracted. Since part of the extractednonsugar substances is precipitated during thejuice purification step, a higher sugar yield isalso achieved with better desugarization [84].
Sugar 19
The extraction time should be short to avoidthe prolonged action of heat, which increases thesolubility of the structural substances of the cos-settes. However, extraction times for the solidphase of 70–75 min, and up to 130 min withsome equipment, are required to attain good ex-traction efficiency. The extraction water used toproduce the juice should be free of thermophilicbacteria and preheated to 65–72 ◦C. The purecondensate obtained on evaporation of the thinjuice is well suited to this purpose. The extrac-tion water is adjusted to pH 5.6–5.8 with sulfurdioxide, hydrochloric acid, or sulfuric acid.
The ability of the structural substances to bepressed mechanically is improved by convert-ing the carboxyl groups of the pectins as muchas possible to calcium carboxylates. For this rea-son, 350–700 mg/L of calcium ions in the formof calcium chloride or calcium sulfate are usu-ally added to the fresh extraction water [85]. Inthismanner, pressed pulpwith a solids content of28–35% can be produced by purely mechanicalmeans. Since about 90% of the salts and acidsin the extraction water pass into the raw juiceand are only partially precipitated during juicepurification, a high salt content in the extractionwater lowers the purity of the thin juice.
The beet-based quantity of extraction wateris calculated as follows:
Quantity of extraction water in% (beet based)= raw juice draft in% (beet based)+ pressed pulp obtained in% (beet based)−100
Water quantities of 25–30% (beet based) areused. Apart from the fresh extraction water, the“press water” serves as an extraction liquid. Thiswater is obtained on pressing the desugarized“wet pulp” from 7–9% solids content to 18–35% solids content (pressed pulp). Since thepress water contains 0.6–2.5% sugar, it must bereturned to the extraction system “below” thepoint of addition of extraction water. Depend-ing on the initial and final solids content of thepressed pulp, 35–65% (beet based) press wateris obtained. The press water cycle, including theentire pulp pressing station, is very susceptibleto infection. For this reason, efforts are madeto have short residence times (small pump re-cipients, short piping, no collection boxes, etc.)and to reheat the press water to 68–71 ◦C asquickly as possible. The advantages of recyclingthe press water compared to using only fresh
water are no accumulation of wastewater dur-ing extraction, a lower extraction water require-ment, an increase in the pressed-pulp solids ob-tained by 0.3–0.4% (beet based), higher-qualitypressed pulp that contains about three times thesugar of pressed pulp obtained by using onlyfresh water (sugar content of 6% compared with2% of the solids), and lower extraction losses.
The mathematical control of juice produc-tion includes daily determination of the extrac-tion losses, the amount of pressed pulp obtained,and the raw juice draft in percent (beet based).In addition, the sugar content (polarization, Pol)and the dry substance (DS) of the fresh cossettes(FC), pressed pulp (P), and raw juice (RJ) mustbe determined analytically. Although rare, theamount of pressed pulp obtained can also be de-termined byweighing. According to the calcula-tion proposed by F. Schneider [86], the amountof sugar X1 obtained in the raw juice is deter-mined first:
X1 =PolFC·DSp−Polp·DSFC
DSp−Polp·DSRJPolRJ
(in % Pol, beet based)The extraction loss is then
X2 = PolFC−X1
the raw juice draft is
X1
PolRJ·100
the pressed pulp obtained is
X2
PolP·100
all three in weight percent, beet based. Theseformulas are valid only in a closed system (i.e.,when no wastewater is produced).
7.2. Extraction Technology
The batchwise operating diffusion battery (→Liquid–Solid Extraction) has now been largelyreplaced by continuous extraction systems (seebelow). Diffusion batteries consist of 8–16cylindrical vessels that have a conical top andbottom, and a net capacity up to 12 m3. Exceptfor two diffusers that are, in each case, beingemptied or filled with fresh beet cossettes, allthe others are connected in series to a battery.
20 Sugar
The juice flows from the top to the bottom coun-tercurrently to the slices.
The continuous extraction process was in-troduced to reduce extraction losses, to avoidwastewater (effluent water), and for purposes ofrationalization. Continuous extraction systemscan be divided into equipment without cossette-forced charging, equipmentwith cossette-forcedcharging, and equipment with cossette- andjuice-forced charging [87].
In equipment without the forced charging ofcossettes, the extraction liquid flows steadilycountercurrent to the cossette mass. The cos-settes are transported within the extraction areawith relatively simple internals (e.g., screws).Examples of this type of equipment are theBMA tower, the Buckau-Wolf tower, and theDdSdiffuser. TheBMA tower and theDdS slopediffuser are described here (Sections 7.4.1 and7.4.2).
In equipment with forced charging of cos-settes, the cossettes are drawn through the ex-traction area with a special transport system,which consists of endless chains with convey-ing elements. The Olier system belongs to thistype of equipment and is similar in design to achain conveyor extractor (→ Liquid–Solid Ex-traction).
Systems with forced charging of cossettesand juice consist of a number of cells in whichthe material being extracted and the extrac-tion liquid move cocurrently for a time. How-ever, countercurrent extraction is obtained on thewhole because the extraction liquid or the feedis, in each case, returned to the preceding cell[88]. Examples of this type of system are the RTcontinuous drum [89, 90] and the De Smet dif-fusion system (see Section 7.4.3), which is alsocalled trickle diffusion.
The best technological results have been ob-tained with further development of the RT con-tinuous diffuser. However, this system requiresthe highest specific investment costs and hasthe greatest space requirement. Throughout theworld, extraction towers,DdS slope, andRT sys-tems are most frequently installed in beet sugarfactories.
For a survey of the historical development ofequipment and machines for the extraction ofjuice, evaporation, crystallization, and separa-tion, see [90].
7.3. Extraction with NonaqueousSolvents
Extraction with nonaqueous solvents has notachieved commercial importance although ap-propriate experiments with methanol, ethanol,mixtures of these with polyhydric alcohols [92],and liquid ammonia [93] as extracting agenthave been conducted repeatedly on a pilot scale.Since these processes can only use dried beetcossettes, they are not profitable because of thehigh costs of drying and storing cossettes, de-spite the possibility of year-round operation.
7.4. Extraction Systems
Extraction plants are complex. They consist of:
1) The actual extraction equipment2) The system for denaturation of the beet cells,
which is used simultaneously as a heat ex-changer to obtain raw juice that is as cold aspossible
3) The pulp pressing station, the resulting presswater being returned to the extraction step
7.4.1. BMA Extraction System [90]
TheBMAextraction system, supplied byBraun-schweigische Maschinenbauanstalt AG, Braun-schweig, is depicted in Figure 5.
“Fresh cossettes” from the slicer (a) are de-natured in a horizontal countercurrent mixer (c)with the “tower juice”, which is warmed up inthe preheater (f). The cossette–juice mixture isdeaerated and brought to extraction temperaturebefore being pumped (h) into the bottom of theextraction tower ( j). The tower juice cools downin contactwith the cold cossettes,washes the celljuice out of the opened beet cells by convection,and is withdrawn from the system as raw juice at20–30 ◦C through a front screen and via pump(g).
In the extraction tower, the cossette mass isled from the bottom to the top countercurrentlyto the extraction liquid with the help of suit-able internals (e.g., a rotatable tube inside thetower with stirring arms that interact with baffleplates connected to the outer wall). The extrac-tion freshwater fed at the top and press water fed
Sugar 21
Figure 5. Flow diagram of a BMA extraction planta) Slicer; b) Belt conveyor with scale; c) Countercurrent cossette mixer; d) Defoamer; e) Pump for defoamed juice; f ) Pre-heater; g) Pump for raw juice; h) Pumps for cossette–juice mixture; i) Sand separator; j) Extraction tower; k) Screw conveyor;l) Pulp press; m) Belt conveyor; n) Tank for press water; o) Pump for press water; p) Tank for fresh water; q) Pump for freshwater—- Circulation juice; ••••••••• Raw Juice;——-Fresh water; – · – · – · Press Water;—- Vapor; ◦◦◦◦◦◦◦ Vent
a little lower down are preheated (65–70 ◦C) sothat the extraction tower need not be heated.
The desugarized cossettes are discharged atthe top and led via screws to the pulp pressingstation, where they are pressed to give pressedpulp with a solids content of 18–22%, if useddirectly, or 22–35% if dried.
The press water is freed of smaller beet marcparticles by rotating or vibrating screen surfacesor sieve-bend screens. It is then heated in pre-heaters and returned to the extraction system.The pH of the press water should be 5.0–5.5.If the pH is higher, it is adjusted by addition ofacid, as in the case of freshwater extraction. If thepH is lower, the press water cycle contains bac-teria and must be disinfected. But after a rapidincrease of energy costs in 1973, some sugarfactories started to operate towers with inten-tional growth of microorganisms and concomi-tantly lower pH of press water to improve pulppressing [91].
Extraction plants of this type were built witha maximum beet processing capacity of 12 000t/d, but are often operated at higher than nomi-nal rates. The extraction tower has a diameterof 11.0 m and a height of 21.6 m; the coun-tercurrent mixer has a diameter of 6.7 m and alength of 8.5 m. The tower and circulation juiceare about 1000% (beet based) in circulation.For this reason, the circulation juice has to be
heated by only ca. 2–3 K to introduce the re-quired amount of heat. The time of extraction is70–85 min, including 8–10 min in the scalder.At a raw juice draft of 106–115% (beet based),extraction losses of 0.19–0.25% (beet based) areobtained.
7.4.2. Extraction with the DdS SlopeDiffuser [90, 94]
In contrast to extraction towers, the DdS slopediffuser (Fig. 6) of the De danske Sukkerfab-rikker, Copenhagen, consists of a single pieceof equipment, a trough (apart from the cos-sette pressing station). This trough is inclinedat about 8◦; it is ca. 25 m long, and 4–7 m wide.The cossettes are transported from the bottom tothe top against the flow of extraction liquid bytwo parallel interworking transport screws. Thetrough is heated by 12 steam caps attached to itsouter jacket. Because of the good heat exchangethroughout the trough, this system made it pos-sible for the first time to obtain raw juice witha temperature of 20–25 ◦C. At a raw juice draftof 109 to 116% (beet based), extraction lossesof 0.14–0.26% (beet based) are obtained [95].A disadvantage of the DdS slope diffuser is thelong residence time of the cossettes in the ap-paratus (about 125–140 min). These plants are
22 Sugar
Figure 6. Schematic of DdS slope diffuser [95]a) Belt weigher; b) Belt conveyor; c) Cossettes bin; d) Screw conveyor; e) Steam cap; f ) Control valve; g) bucket wheel fordischarge of desugarized cossettes; h) Screen; i) Raw juice draft; j) Extraction freshwater inlet; k) Press water inlet
built up to a beet processing capacity of 5000t/d.
7.4.3. Extraction with the De Smet System
The De Smet system(→ Liquid–Solid Extrac-tion) belongs to the type with forced charg-ing of cossettes and juice. A compact cossettelayer with a height of 60–70 cm is moved inter-mittently forward at a speed of 3.2 cm/min onthe upper part of an endless, horizontal wedge-wire screen (ca. 5 m wide, total length 75 m)moving on two guide rolls. The extraction liq-uid trickles constantly through the entire cos-sette layer from the top downward in 18 partialstreams. The liquid is collected under the screenin compartments and pumped into the juice gut-ter above the next compartment against the cos-sette flow. From here, the juice again tricklesthrough the cossette layer. In this manner, coun-tercurrent extraction is achieved on the whole,although cocurrent extraction occurs in individ-ual steps. With a raw juice draft of 108–115%,sugar losses of 0.14–0.30% (beet based) are ob-tained [87].
7.4.4. The RT-5 Continuous Extractor
The RT-5 extractor [88 – 90] consists of a ro-tating cylindrical drum having a double screwsystem, similar to an Archimedes screw, weldedto its inner wall. Thus, the residence time of theextraction liquid is very short (≈ 30 min), andthe residence-time distribution is very narrow.The cossette mass is present in weighed partialamounts in each of the “compartments.” Witheach rotation, it is lifted out of the extraction
liquid and transported forward by two compart-ments with the help of grates (screens) (numberof compartments ≈ 35). To ensure smooth op-eration of the drum, the lifting of cossette pack-ets is carried out in accordance with the numberof compartments, staggered in time, over a pe-riod of one rotation of the drum. This elaboratedesign gives excellent technological values andlow extraction losses at a low raw juice draft.The maximum capacity of the RT-5 extractor is13 000 t of beets per day, the length being 63 m,the diameter of the denaturation compartment8.95 m, and that of the heat exchange compart-ment 7.5 m.
7.5. Pressing Extracted Pulp [82, 96]
Two types of presses exist: The single-screwvertical press and the swing screw horizontalpulp press. The presses consist of a cylindricaljacketwith a screen pack inwhich a conical pressscrew (spindle) rotates (1–4 rpm). The spindle isequipped with spirals and a sieve covering. Thering opening at the end of the press spindle canbemadewider or narrower bymeans of a “cone.”Thus, constant pressure can be maintained witha changing output. Pressing is achieved by thefact that the passage volume is diminished pro-gressively due to the conical form of the spindlebody and the reduction of pitch of the screw.Press water is withdrawn from the screen jacketand press spindle by means of tubing. A single-screw vertical pulp press with a spindle diam-eter of 4 m and a height of 19.6 m can presscossettes from 3000 t of beets per day. Sincethe mid-1960s, a swing screw horizontal press(producedbyStord–Bartz Industri, Bergen,Nor-way), operated according to the double screwprinciple. Today (early 2000s) presses by BMA
Sugar 23
(single screw),Babbini (double screw) andStord(double screw) are installed with maximum ca-pacities of 3500–5000 t/d, based on sliced beetand 30% dry substance in pressed pulp [1]. Ver-tical double screw presses supplied by Babbiniare among the latest developments [97].
Pressed pulp with a solids content up to 35%can be obtained by optimization of the operatingparameters and further development of construc-tion details. Efforts are being made to attain asolids content that is still higher by double press-ing or diffusive dewatering (up to 50%). For thedrying of beet cossettes, see Section 22.5. Foruses, see also Section 22.5.
8. Juice Purification
The raw juice with a solids content of 13–17%has a grayish black, opalescent appearance. Itscolor is caused by melanin, a blackish pigment,which is formed in the presence of air by ty-rosinase (E.C. 1.10.3.1) from the tyrosine in thecell juice via dihydroxyphenylalanine (DOPA)and quinoid compounds. In addition, polyphe-nol–iron complexes contribute to the color ofthe raw juice [98].
The raw juice contains almost all the col-loidally dispersed and molecularly dissolvedsubstances (see Section 7.1) present in thecell juice of the sugar beet. It also containsthe acids and salts present in or added to theextraction water, the metabolic products (l-lactic acid, acetic acid) formed microbiologi-cally during extraction,methanol and acetic acidformed by the demethoxylation and deacetyla-tion of pectin, and suspended particles consist-ing mainly of pectin–hemicellulose–proteins,macroscopic fibers, and cell residue as well assand. The composition of the colloid fractionis largely influenced by the temperature courseused in juice production (see Section 7). Rawjuices have approximately the analytical valuesgiven in Table 6.
Until now, attempts to crystallize sugar di-rectly from the raw juice without juice purifica-tion have not achieved importance [99].
The main purpose of juice purification islargely to remove the nonsugar substances con-tained in the raw juice and thus to increase theratio of sucrose to total solids content (i.e., thepurity of the juice) as much as possible. In this
process, only those processing aids and reactionconditions should be used that, as far as pos-sible, avoid not only the destruction of sucrosebut also the conversion of nonsugar substancesto compounds (e.g., colorants) that impede fur-ther processing of the juice.
Before juice purification, the fibers and cellparticles suspended in the raw juice should be re-moved if possible. These particles would other-wise give rise to degradation products that havea negative effect on juice quality [100]. Sandshould also be eliminated from the raw juice(e.g., by means of hydrocyclones).
The juices are heated to 60 ◦C before purifi-cation. In juice production, efforts are made toobtain a raw juice that is as cold as possible. Forthe first heating residual heat can be used (panvapors of ca. 75 ◦C, condensates), which can-not be utilized otherwise and would save 2–4 kgof steam per 100 kg of beets. However, work-ing with cold raw juice can result in bacterialinfections and, consequently, sugar losses andfiltration problems.
The heating devices used primarily are stand-ing tubular heat exchangers and, increasingly,spiral-plate and plate-type heat exchangers. Thejuice in the heat exchangers should flow with arate of less than 2 m/s so that the sludge particlesagglomerated in the precipitation reactions arenot destroyed again.
8.1. Lime–Carbon Dioxide Treatment
Colloidally dispersed or molecularly dissolvednonsugar substances can be precipitated out ofthe raw juice with additives. Of the many sub-stances that have been tested (see, e.g., [101]),only quicklime,whichwas introducedmore than100 years ago, is of industrial importance. Itis available everywhere, and its activity, cheap-ness, and easy applicability cannot be surpassedby any other substance. Furthermore, the car-bon dioxide (CO2) used today solely to removeexcess lime from the juices (carbonation) is ob-tained as a side product (lime kiln gas) in theproduction of quicklime from limestone. Forthis reason, juice purification generally refersto lime–carbon dioxide treatment. Even ion-exchange processes have not been able to dis-place lime–carbon dioxide juice purification, al-though only 30–40%of the nonsugar substances
are removed by the latter process, whereas ionexchange eliminates up to 85%.
An optimal juice purification with lime–carbon dioxide should simultaneously fulfill thefollowing requirements as far as possible [102]:
1) Precipitation or flocculation of the pectin–hemicellulose–protein complex and otherhigh molecular mass nonsugar substances(araban, galactan, etc.).
2) Precipitation of anions, such as phos-phate, sulfate, citrate, malate, oxalate, poly-galacturonates, that give poorly soluble cal-cium compounds with calcium ions, and pre-cipitation of magnesium ions as magnesiumhydroxide. The higher the content of an-ions precipitable with CaO in proportion tothe total anion concentration, the greater isthe excess of alkali ions (potassium, sodium)present in the second carbonation (see page26) in the form of carbonate and hydro-gencarbonate salts. This is connected with alow residual lime content in the thin juice.About 30% of the total cations and 40% ofthe nitrogen-free anions of the raw juice areprecipitated during juice purification.
3) Alkaline degradation of invert sugar, galac-tose, and, partially, galacturonic acid presentin the raw juice. In this process, ca. 1.9meq of acid – 50% of which is lactic acid(racemic mixture of d- and l-lactic acid) –is obtained from 1 mmol of saccharide. Fur-thermore, formic, acetic, arabonic, and sac-charinic acids are formed. Lighter thin andthick juices are obtained by degradation ofinvert sugar in the presence of atmosphericoxygen. In this way the formation of degrada-tion products bearing carbonyl groups is pre-vented, which can immediately react with theamino acids in the juice to give precursors ofMaillard products [103].
4) Hydrolysis of glutamine to pyrrolidonecar-boxylic acid and, in part, of asparagine to as-partic acid.All known juice purificationmeth-ods fulfill this requirement incompletely be-cause the temperatures, residence times, andpH values used during juice purification arenot sufficient for glutamine hydrolysis. Al-most complete glutamine hydrolysis occursonly during the first two steps in the evapo-rator station, with all the accompanying dis-advantages. These include lowering of thepH of the thick juice and re-formation ofinvert sugar, with subsequent colorant for-mation and corrosion in the evaporator sta-tion. The ammonia generated in glutaminehydrolysis passes over with the vapor con-densates (ammonia content 100–200 mg/L).The other amino acids present in raw juiceare influenced only slightly during juice pu-rification. Ornithine and lysine are prefer-entially incorporated into Maillard products.Small amounts of glycine and γ-aminobutyr-ic acid are formed from threonine and ser-ine or glutamine via pyrrolidonecarboxylicacid and its decarboxylation product [104].γ-Aminobutyric acid further reacts with galac-turonic acid or its oligomers to give tagaturon-γ-aminobutyric acid or its derivatives. Theseare intermediates in theMaillard reaction thatgives rise to very highly colored compounds[102].
5) Other nonsugar substances that are not pre-cipitated in the first carbonation, primarilycolorants and multivalent anions (citrate, ox-alate, etc.), should, if possible, be adsorbed onsludge particles or on the surface of freshlyformed calcium carbonate crystals (secondcarbonation).
6) Prevention of chemical [102] and bacterialdegradation of sucrose.
RGC
Resaltado
Sugar 25
Apart from these chemical requirements, op-timal juice purificationmust also produce an eas-ily settleable and filterable sludge.Almost all thechemical analytical values (e.g., color, residuallime content) deteriorate when filtration prob-lems occur, and turbid juice is obtained (witha turbidity level > 10 mg/L). In classical juicepurification, safe filtration can be achieved onlywhen part of the precipitate formed in the firstcarbonation is returned to the preliming stage.
The requirements for optimal juice purifica-tion presented above are influenced by processengineering parameters, such as the following:
1) The total mass of calcium hydroxide addedand distributed to the individual process stepsdetermines the activity of calcium ions andthe pH of the juice in the individual juice pu-rification steps.The CaO required for juice purification is 70–90%, based on the mass of the nonsugar sub-stances introduced with the raw juice. Thiscorresponds to about 0.8–1.3 kg of CaO per100 kg of beets. Of the total CaO mass, 10–12% is added for preliming, 5–7% to the thinjuice 1 (see page 26) before the second car-bonation, and the rest for main liming.Only the Ca(OH)2 content dissolved in thejuice is chemically active. Since calcium hy-droxide ismore soluble in cold sugar solutionsthan in warm solutions (35 g of CaO per literof thin juice at 30 ◦C compared with 5 g ofCaO per liter at 80 ◦C), the addition ofmilk oflime and the “chemical reaction steps” shouldbe carried out at the lowest possible temper-ature. The rate of dissolution of calcium hy-droxide in juice depends on the compositionof the quicklime (magnesium, aluminate, andsilicate content), the burning conditions (hardor soft burning), and the lime slaking tech-nique used, especially the temperatures aris-ing in the pores of the quicklime.
2) The volume of carbonation slurry or slurryconcentrate returned to the preliming step. Ingeneral, the amount of precipitate returned tothe preliming stage with the first carbonationslurry or slurry concentrate is such that the to-tal CaO content in the preliming step is 8–12g/L.Apart from this recycling of carbonationsludge to improve the filtration properties ofthe juices, the juice must be circulated, espe-
cially within the first carbonation, to achievecomplete dissolving of calcium hydroxideparticles. In general, circulationof six to seventimes the quantity of juice via a detentionvessel is sufficient. This measure also pre-vents calcium hydroxide particles from beingsheathed by calcium carbonate crystals in thefirst carbonation and prevents secondary re-actions during further processing of the firstcarbonation slurry (incrustation of the filtercloths, etc.). Furthermore this measure im-proves the exchange of materials during car-bonation.
3) The temperature course during the individualsteps of juice purification. Generally, the col-ors of thin and thick juices are better whenthe first steps of classical juice purification(preliming and main liming) are carried out atlower temperature (30–40 ◦C). Today, for fueleconomy reasons, a temperature of 55–60 ◦Cis generally used for preliming.Main liming isconducted at 85 ◦C. A temperature of 85 ◦Cis also used for the first carbonation. If theheat loss in the first carbonation is very high,the first carbonation slurry should be heated to85–90 ◦C to obtain better filtration properties.The second carbonation should be conductedat ≥ 94 ◦C.
4) The residence time during the individual pro-cess steps (i.e., the average residence time andthe residence-time distribution in the case ofcontinuous operation). The usual average res-idence time for the individual process steps is
Preliming 20 minCold main liming 5 minHot main liming 20 minFirst carbonation 15 minAddition of lime before second carbonation 5 minSecond carbonationBubble column 12 minReaction vessel 10 min
87 min
5) The composition of the carbonation gas (car-bon dioxide and oxygen content) and the typeof gas distribution in carbonation. These sub-stantially influence the exchange of materials(gaseous–liquid and liquid–solid) and the ex-ploitation of carbonation gas.In the carbonations, for precipitation of thecalcium hydroxide mass mentioned above,3.41 kg of lime kiln gas per 100 kg of beets is
RGC
Resaltado
26 Sugar
required in the first carbonation, and 0.72 kgper 100 kg in the second, if the lime kiln gashas a CO2 content of 40 vol%. For the prod-uct of the liquid side mass-transfer coefficient(kL) times the specific interface (a) for car-bonations used today, the following kL×a val-ues are calculated:≈ 250 h−1 for the first car-bonation and≈ 50 h−1 for the second carbon-ation at superficial velocities of v0 = 30–40cm/s for the first carbonation and v0 = 8–10cm/s for the second.Compared to bubble columns used in other in-dustries, the kL×a values for the carbonationsare too low, and the superficial velocities toohigh. This means that the design of the actualcarbonation vessels (bubble columns) is notyet optimal.The values also imply that the installationof mechanical stirrers cannot produce an im-provement in the operation of carbonationvessels, especially for the second carbonation.The average crystal diameter and the crystal-size distribution of the calcium carbonate pre-cipitates formed in the carbonations dependon the temperature and the calcium ion con-centration in the juice. The higher the tem-perature, the coarser are the crystals, and thehigher the calcium ion concentration, the fineris the average crystal diameter. Presently, theaverage crystal diameter obtained (mass dis-tribution) is between 7 and 10 µm.
6) The manner in which carbonation sludge isseparated from the juice, i.e., whether directfiltration is employed, e.g., via chamber fil-ter presses (→ Filtration), with decanters anddrum filters (→ Filtration, Chap. 8.6), withthickening filters and drum filters, with pressfilter automatic machines (→ Filtration), ormembrane filter presses. During the contacttime of the precipitated nonsugar substanceswith the juice, partial redissolving of the pre-cipitate and other undesirable chemical reac-tions occur, including acid formation by alka-line degradation of nonsugar substances andsugar. For this reason, the separation of pre-cipitate and juice should occur quickly.
7) The design of the equipment for individualprocess steps [102]. This applies not only tothe reaction vessels, but also to pumping ves-sels, intermediate containers for juice, etc.These vessels should be designed in accor-dance with the principle “first in, first out.”
8) Themaintenance of optimal pH values duringpreliming, and first and second carbonation,which substantially influences the success ofjuice purification.The industrial purification process consists of
individual operations. Apart from the main pro-cesses described below, numerous process vari-ations are known.
Classical Juice Purification. Classicaljuice purification consists of preliming, mainliming, first carbonation, first sludge separa-tion, second liming, second carbonation, sec-ond sludge separation, possibly sulfitation, andsafety filtration. The process is represented sche-matically in Figure 7.
Preliming. In the preliming operation, rawjuice is subjected to stepwise alkalinization withmilk of lime (ca. 200 g of CaO per liter) up to aconcentration of 0.12–0.25 wt% CaO, based onthe juice. Today, progressive preliming is usedalmost exclusively (i.e., the pH of the raw juiceis raised slowly from 6.2 to 10.8–11.4). The op-timal pH to be maintained can be determined inthe laboratory [105]. The optimal pH for the firstcarbonation is determined in a similar manner.
For preliming, horizontal U-shaped troughs[106] or vertical cylindrical vessels [102, 107],with forced charging of the juice, are used. Inboth cases, milk of lime is added at the end ofpreliming, and the pH steps in the individualcompartments are achieved by back-mixing ofa part of the juice in each case. The slow step-wise increase in pH from 6.2 to 11.4 has provedadvantageous for effective precipitation and forstabilization of the precipitated substances be-cause the colloids present in the raw juice haveno uniform coagulation optimum.
The carbonation sludge to be recirculatedshould be added to the juice at pH 8–9 so that thecolloids that start to precipitate are already pro-vided with adsorption surfaces such as CaCO3crystals. In addition, the sludge particles re-turned are “overcarbonated”due to the lower pH,becomingdehydrated and less soluble. Themorecarbonation slurry concentrate or slurry is circu-lated, the better are the sedimentation and filtra-tion properties of the juice. Less than the newlyproduced carbonation sludge should be circu-lated (i.e., no more than 1 volume of slurry pervolume of raw juice in the case of carbonationslurry or 0.15–0.25 volumes per volume of raw
Sugar 27
Figure 7. Schematic of juice purificationa) Preheater; b) Prelimer; c) Main limer (cold); d) Main limer (hot); e) 1st carbonation, reaction vessel; f ) 1st carbonation, pri-mary tank; g) Recirculation pump; h) Pumping tank; i) Thickening filter; k) Drumfilter; l) 2nd liming tank;m) 2nd carbonation,reaction vessel; n) 2nd carbonation, primary tank; o) 2nd carbonation, holding tank; p) 2nd filter; q) Safety filter
juice in the case of slurry concentrate). The recy-cling causes simultaneous juice dilution, whichhas a favorable effect on colloid flocculation.
Most of the nonsugar substances are precip-itated in the prelimer; i.e., the purity of juicesranging from normal to thin juice 3 (see Sec-tion 8.1) differs only slightly from that of theclear preliming juice. However, the prelimingfloc formed can be separated from the juice onlywith difficulty.
Only in the Sepa process [108] is the carbon-ation sludge separated after the preliming op-eration. In this process, the preliming precipi-tate is dried together with molasses on pressedpulp (see Section 22.5) and then used as feed.The preliming juice is heated to 90 ◦C and sub-jected to defeco- carbonation (see Section 8.2.1)to load the flocculated colloids. However, theCaO added should not cause the total CaO con-centration in the juice to exceed 0.5–0.6%. Thecarbonation slurry obtained in this way is thick-ened with the help of decanters, and the result-ing slurry concentrate is again concentrated inself- cleaning disk centrifuges. The thick sludgewith ca. 78% settleable substances is filteredthrough drum filters, and the desweetened fil-ter cake is very finely dispersed in ca. 1.8% ofmolasses (beet based). The homogenized mix-ture is sprayed onto pressed pulp. The clear juice
from the decanter and filter is again subjected todefeco- carbonation, the juice being further pro-cessed as in normal juice purification processes.This method gives strongly colored thick juices.
Main Liming. In the main liming operation,CaO is added to the juice up to an alkalinityof 0.8–1.3 wt% CaO, which results in a totalCaO concentration in the main liming juice of1.8–2.5 wt%.Apart from the chemical reactionsat high alkalinity, especially the destruction ofinvert sugar and amide hydrolysis, calcium hy-droxide causes the formation of somuch calciumcarbonate in the first carbonation that the slimyflocculate formed during preliming becomes en-meshed and filterable. Since 2002, lime additionis often controlled by the filterability of juice,according to the LIMOS method [109], in or-der to lower the gross consumption of limestone(CaCO3) to values < 2.5% (beet based).
For the main liming operation, the vertical orhorizontal vessels used are connected in a cas-cade and provided with slow stirrers [104]. Theduration of main liming depends on the temper-ature: the residence time of the juice should beabout 25 min at 80–85 ◦C or 15 min at highertemperature (up to 92 ◦C).
As a result of the better dosing ability, CaOis now added almost exclusively in the form ofmilk of lime (wet liming). The dry liming pro-
28 Sugar
cedure used earlier, in which the quicklime wasslaked directly in the juice, is seldom employed[110] because local overheating could cause su-crose destruction and discoloration of the juice.
First Carbonation [111]. In the first carbon-ation, excess calcium hydroxide in the juice ispartially converted to calcium carbonate withcarbon dioxide (carbonation gas). Thus, a filteraid for enmeshing the precipitated colloids (seeabove) and a surface for the adsorption of non-precipitable nonsugar substances are produced.Furthermore, part of the ammonia – formed inthe main liming by hydrolysis of the amides –and other gaseous organic substances are elimi-nated from the juice by the passage of carbona-tion gas. The resulting saturation of the exit gaswith water vapor is connected with a heat loss ofca. 6000 kJ per 100 kg of beets. This can, how-ever, be avoided bymeans of a suitable switch inthe process flow [112]. The end point of the firstcarbonation is reached at pH 10.8–11.4, whichcorresponds to an alkalinity of 0.07–0.12% ofCaO in the filtered juice (thin juice 1). At lowerpH (overcarbonation), part of the precipitatedcolloids is redissolved and the quality of the juicedeteriorates. The temperature of the first carbon-ation should be 85 ◦C.
To exploit the carbonation gas sufficiently (≈85%), it is passed countercurrently at a juicelevel of 5–6 m through the juice that enters fromthe top.
First Sludge Separation. After the first car-bonation, the first carbonation slurry, which isheated to 90–95 ◦C and has a sludge content of50–60 g of solids per liter, depending on sludgerecycling, is separated in decanters into clearjuice and slurry concentrate. The decanter vol-umes required are about 100–120%of the slurryvolume. Suitable decanters are thickeners withrakes or thickeners without forced dischargingof the slurry concentrate. The concentration ofsludge in the slurry concentrate is 2.5–5 timesthat in the carbonation slurry.
Sludge separation can be simplified by theuse of “thickening filters,” which immediatelygive a filtrate free from turbidity and a greatlythickened slurry concentrate. In thickening fil-tration, the carbonation slurry is filtered directlythrough continuously and batchwise operatingfilters. Thus, the residence time of the juice inthe decanter is eliminated, and no heat is lostdue to cooling. The level of turbidity in the fil-
trate obtained is generally so low that postfiltra-tion is unnecessary. The sludge content of theslurry concentrate from filter thickeners is fiveto seven times that of carbonation juice. Cloth-covered tube filters are used preferentially forthickening filtration [113].
Of the total slurry concentrate obtained, ca.45 vol% is returned to the preliming stage, andabout 55 vol% is filtered throughmulticompart-ment or single- compartment drum filters (vac-uum or pressure drum filters). In this process,20–30 m2 of filter surface is required for 1000t of beet processing per day, depending on thesludge content of the slurry concentrate. The ca-pacity of vacuum drum filters is 0.5 m3 of clearjuice per square meter per hour.
The carbonation sludge is washed on drumfilters with about 80–100% of hot water (con-densate), based on the sludge volume, until asugar content of 0.1–1.0% is attained (desweet-ened). Depending on the lime added in juice pu-rification, 8–10% (beet based) of sludge is ob-tained with a solids content of 45–50%.
The decantated material (level of turbidity50–100 mg/L) and the drum filter filtrate (levelof turbidity 200–500 mg/L) are refiltered sepa-rately or together through ceramic or cloth- co-vered tube filters (→ Filtration) or bag filters (→Filtration). The level of turbidity in the postfil-tered juices is less than 10 mg/L. In the case ofcloth- covered filters, the capacity is ca. 2–3 m3
m−2 h−1. If thickening filters are used, the drumfilter filtrate is returned to the first carbonation.
To immediately obtain a spreadable carbon-ation lime cake that can be used as fertilizerlime, automatic membrane filter presses (→ Fil-tration) or automatic press filters (→ Filtration)[114] are being used increasingly for filtrationof the slurry concentrate. These automatic ma-chines produce “carbolime” with a solids con-tent of > 70% and a CaO content of > 30%,which is a suitable fertilizer lime. The composi-tion is given in Table 12.
Second Carbonation. In the second carbona-tion step, more carbon dioxide is led into the fil-tered juice from the first carbonation to convertthe remaining calcium hydroxide to carbonateand, in addition, to transform the alkali present inthe juice, mainly potassium hydroxide, into hy-drogencarbonates or carbonates. In a secondaryreaction, the calcium bound to organic acids orcomplexes is partially precipitated as carbonate.
Sugar 29
A sufficiently low residual lime content can-not always be attained in the thin juice 2 (<30mg CaO/100 g DS). Further softening can beachieved by adding aqueous sodium hydroxide–sodium carbonate to thin juice 1 or by ion-exchange treatment of thin juice2 (see Section14.1).
To increase the adsorption of nonsugar sub-stances by increasing the calcium carbonatecrystal surface and to improve the filtration prop-erties of the second carbonation juice, 0.1–0.2%CaO, juice based (after filtration of the first car-bonation juice), is added to thin juice 1 beforethe second carbonation. The temperature of thesecond carbonation should be 94–98 ◦C. A pHbetween 8.9 and 9.2 (alkalinity 0.015–0.022%CaO) is maintained as the end point of the sec-ond carbonation, atwhich the remaining residuallime content in the filtered juice (thin juice 2) isat a minimum.
The juice reaching the second carbonationmust not contain any sludge particles (i.e., itmust be free of turbidity after filtration) becausethese particleswould otherwise redissolve. Evenvery little residual sludge produces the juiceshade characteristic of overcarbonation and anoticeable deterioration in color [115].
As in the first carbonation, cylindrical ves-sels with a juice level of 5–6 m are also usedin the second carbonation. In contrast to thefirst carbonation, the second is often carried outcocurrently, juice and carbonation gas being in-troduced into the vessel from the bottom. Thejuice from the second carbonation flows througha holding tank, a cylindrical vessel with a cen-tral tube, which contains a propeller mixer. Thismixer circulates the juice 20 times from the bot-tom to the top to mechanically remove from thejuice the carbon dioxide liberated by the chang-ing of the CO2−
3 –HCO−3 equilibrium.Control of Carbonations. The optimal end
points of the first and second carbonations aredetermined experimentally. Addition of carbon-ation gas is controlled by continuous measure-ment of pH.
Second Sludge Separation. Since the amountof carbonation sludge obtained on filtration ofthe second carbonation slurry is only 2–5%of that obtained on filtration of the first slurry(in cases where no calcium hydroxide is addedin the second carbonation), slurry 2 is usuallyfiltered directly through cloth- covered filters.
Only in exceptional cases is it preseparated indecanters into clear juice and slurry concentrate.The sludge obtained is not “desweetened” in fil-ters, but is either recirculated to the prelimingstage or added to slurry concentrate 1, which isthen filtered and desweetened.
Sulfitation. In some factories, the next stageis a so- called third carbonation. This comprisesthe treatment of the juice with gaseous sulfurdioxide to adjust the pH and brighten the color(prevention of excessive discoloration duringsubsequent evaporation). This step should beperformed only if the pH of the thin juice isso high (pH > 9.2) that after evaporation (seeSection 9) an alkaline thick juice (pH > 8.8)would be obtained. If the pH is not so high, itmust be raised by the addition of soda (50–200g per cubic meter of juice). The amount of SO2added should not exceed 50 g per cubic meterof juice. Otherwise, the pH of the juice can de-crease sharply during evaporation, which causescorrosion. The exact amount of sulfur dioxide isusually added at the lowest point of a U-shapedpipe via a control valve. The SO2 inlet pressureis kept constant by heating the SO2 storage tankto a certain temperature (e.g., 30 ◦C ∧= 471 kPa).
Safety Filtration. If the thin juice is sulfur-ized, it must be filtered again before evaporationto remove precipitated calcium sulfite, whichwould otherwise result in strong scaling in thefirst stage of the evaporating station. Safety fil-tration is recommended, even in the absence ofsulfitation. Tube filters that are precoated witha filter aid are an advantage. The level of tur-bidity (water-insoluble solids> 0.45 µm) of thefiltered thin juice 3 is less than 10 mg/L.
8.2. Other Juice Purification Processes
8.2.1. Simultaneous Defeco-Carbonation
Simultaneous defeco- carbonation refers to juicepurification processes in which the raw juice,heated to 85–90 ◦C, is simultaneously treatedwith lime and carbon dioxide, while an exactor only slightly fluctuating pH value is main-tained. In contrast to classical juice purification,in defeco- carbonation the colloids are precipi-tated in the presence of carbon dioxide in sucha manner that the sludge particles are enmeshedimmediately by calcium carbonate crystals. The
30 Sugar
conglomerates thus formed are generally larger,better dewatered, and more solid than the sludgeparticles in classical juice purification. There-fore, the sedimentation and filtration propertiesof these sludge particles are very good. On theother hand, the resulting juices are only slightlythermostable because of incomplete destructionof invert sugar and low amide hydrolysis. Theyare stronlgy discolored in subsequent process-ing steps so that much darker thick juices areobtained.
Simultaneous defeco- carbonation is carriedout according to the Dorr system, especially inthe United States and the United Kingdom. Theheated raw juice, together with six to eight timesthe amount of slurry, is first pumped into the bot-tom of a mixing vessel (primary tank), which isas large as the subsequent carbonation vessel. Inthe primary tank, a pH of ca. 10 is attained. Milkof lime (1.0–1.6%CaO, juice based) is added asthis juice mixture overflows into the actual car-bonation vessel. Here, the juice is carbonatedcountercurrently to an optimal pH of 10.8–11.4.The finished juice is withdrawn from the bottomof the carbonation vessel. About six-sevenths ofthe juice is returned to the primary tank as circu-lated juice, and one-seventh proceeds to sludgeseparation. Further process steps correspond tothose of classical juice purification.
8.2.2. Braunschweig Juice Purification
A further development of the Dorr system, theBraunschweig juice purification process, is usedoccasionally in Europe [116]. In addition to re-turning the slurry to the mixing vessel of theDorr system, this process also requires the thicksludge to be recirculated to the raw juice in aseparate mixing or reaction vessel located ear-lier in the process flow.Before carbonation at pH10.8–11.2, the raw juice colloids pass throughtwo separate pH steps during the thick sludgerecycling (pH = 9) and the slurry recycling (pH= 10). Here, too, juices with very good sedimen-tation and filtration properties are obtained. Thedestruction of invert sugar, as in main liming,does not occur, which means that thermolabilejuices are again obtained.
8.2.3. Defeco -Carbonation withIntermediate or Post Main Liming
The idea of combining the advantages of clas-sical juice purification (attainment of ther-mostable juices that are free from invert sugarand have a good color) with the advantagesof defeco- carbonation (good sedimentation andfiltration properties of the precipitates produced)led to the development of other combination pro-cesses.
In the Braunschweig juice purification pro-cess (see Section 8.2.2), stabilization of the floc-culated colloids is so good that defeco- carbon-ation for chemical stabilization of the juices canfollow without impairing the filtration ability ofthe resulting carbonation slurry. For this reason,in one of the combination processes, before theseparation of the precipitate, another addition oflime (main liming) to the slurry –which causesthe pHof the juice to increase to> 12.5 for a cer-tain time [117] – is carried out before a furthercarbonation step (pH 10.8–11.2).
In the Novi-Sad juice purification process(former Yugoslavia) [118], efforts are madefirst to flocculate the precipitable nonsugar sub-stances in a type of defeco- carbonation; the pre-cipitate is subsequently separated, and the juiceis chemically stabilized in a main liming step.The lime is added as follows: 1.0–1.3% of CaOis added in the defeco- carbonation, and 0.6–0.7% of CaO (beet based) is used for chemicalstabilization in the main liming step. The pre-cipitate obtained after main liming in a normalfirst carbonation at pH 10.8–11.2 (i.e., mainlycalcium carbonate) is separated with decanters.The resulting slurry concentrate (ca. 10–14%,juice based) is returned to the defeco- carbona-tion. In this way, the entire sludge obtained canbe filtered through one filtration unit [119].
9. Evaporation of Thin Juice
After purification, the thin juice has a solids con-tent of 15–18%. It is concentrated in a mul-tistage process to a solids content of 68–74%(thick juice), ca. 85–100 kg of water being evap-orated per 100 kg of beets. From ca. 115–130%(beet based) of thin juice, 25–30% (beet based)of thick juice is obtained.
Sugar 31
Table 7. Heat-transfer coefficients of juice (in W m−2 K−1) as a function of total solids content
Evaporated water accumulates as vapor con-densate in the individual effects of the evaporatorstation. It contains about 6–10 mmol/LNH+
4 ,partly as (NH4)2CO3, and varying amounts ofsteam-volatile organic substances [120]. Thecondensate is used as fresh water for extraction,as dissolving water in the sugarhouse (remelt,dilution of syrups, etc.), and as plant water forthe wash and flume water cycles. The surplusmust be treated biologically (see Section 6.8).
During evaporation, the juice generally un-dergoes only slight chemical alteration. The re-maining glutamine is hydrolyzed primarily topyrrolidonecarboxylic acid with elimination ofammonia. At the same time, the pH decreases(danger of sugar hydrolysis), and alkaline andoxidative decomposition of sugar occurs to aslight extent. Calcium salts of various acids(calcium oxalate, citrate, sulfate, and carbon-ate) precipitate, along with SiO2 in some cases,due to the change in solubility conditions. Toprevent the formation of scale on the evapo-rator tubes, calcium complexing agents (antis-caling) are added to the juice (5–10 g per cu-bic meter of juice). During juice evaporation, adark color appears, owing to the formation ofMaillard products [103] (condensation productsfrom reducing carbohydrates and amino acids),Strecker degradation, and caramelization pro-cesses [103]. The discoloration [121] dependsgreatly on juice temperature (it should be <132 ◦C), H+ activity, average residence time,and residence-time distribution.
Steam-heated evaporators of various designs(Robert evaporator, → Evaporation; falling-film, evaporator,→ Evaporation; or plate evap-orator) are used for juice evaporation. They haveheating surfaces of normal or stainless steeltubes, that are smooth or twisted, up to 6000m2 per evaporator. A total heating surface of 2.0to 2.5 m2 is required for 1 t of processed beetsper day.
The evaporators are arranged in multiple-effect evaporator stations in such a way that the
saturated vapor generated in one effect is, in eachcase, used to heat the next effect and other heatconsumers (cocurrent evaporation). The evapo-rator stations consist of four to six effects with apressure drop from ca. 0.35 MPa in the calandriaof the first effect to 0.12 MPa in the calandriaof the last effect. In the process, the tempera-ture of the juice falls from 130 ◦C to ca. 90–95 ◦C. The last effect operates under weak vac-uum.The vacuum is produced by condensing thevapor with a 15–20-fold amount of water in jetcondensers andbywithdrawing thenoncondens-able gases (water-ring pumps, piston pumps). Inindustrialized countries, the heated water (con-denserwater) is recycled after cooling in coolingtowers.
The heating surfaces must be distributed overthe individual effects so that the desired thick-ening of the juice to 68–74% solids content isachieved in the last effect. Also, the entire re-maining saturated vapor requirement of the fac-tory should be coveredbyvapor from the last twoeffects. The size of the heating surfaces in the in-dividual effects must be calculated from case tocase by taking into account the mass flow andthe vapor consumption of the individual vaporusers [122].
Guide values for the overall heat-transfer co-efficient k (in W m−2 K−1) for various solidscontents in the case of rising and downflowevap-orators are given in Table 7. The solids content,which correlateswith the viscosity of the juice tobe evaporated, greatly influences the heat trans-fer coefficient [121].
Because long average residence times andpoor residence-time distributions in the individ-ual evaporators are a disadvantage to the juice[strong discoloration, sugar destruction [123] upto 0.15% (beet based)], efforts were made to de-crease the entire installed heating surface by in-creasing the heat-transfer values or to reduce theresidence time of the juice by using other evap-orator designs (plate evaporator). Values for k of7000–8000 W m−2 K−1 can be achieved for the
32 Sugar
Figure 8. Rate of crystallization of sucrose as a function of supersaturation and temperature at different puritiesA) Purity = 100%; B) Purity = 80%; C) Purity = 60%
first effect and 2500 W m−2 K−1 for the secondeffect by increasing the juice velocity within thepiping [e.g., by forced feeding (Buckau–Wolfcontinuous evaporator)]. Higher k values can beattained by using falling-film evaporators, and asmaller temperature difference is obtained bet-ween the calandria and the vapor space in the in-dividual effects. As a result, the residence timeof the juice is reduced by about half. This ap-plies more to plate evaporators, the average resi-dence time being reduced to 1–2 min per effect,which is only one-fifth that of a Robert evap-orator station [124]. In 1992 an advantageouscombination of plate evaporators and falling-film principle was introduced, and in the fol-lowing years various integrated concepts weredeveloped, with high k values and small heatingsurface, compared to other technology [125].
The steam requirement of the evaporator sta-tion and, therefore, the energy requirement forsugar production depend on the mode of oper-ation of the factory. In the case of white sugarfactories that do not produce refined sugar, therequirement is ca. 20–25 kg of normal steam per100 kg of beets (54 000–67 000 kJ, correspond-ing to 15–18.5 kW · h). In factories with refinedsugar production, this is increased by ca. 10 000kJ, and in raw sugar factories, it is ca. 40 000 kJ.For the steam and energy economy of a sugarfactory, see [126].
The precipitation and partial caking of spar-ingly soluble calcium compounds on the heat-ing surfaces of the evaporators can greatly lowerthe heat-transfer and evaporating efficiency. Inthis case, the heating surfaces must be cleaned(boiled out). The equipment is treated first with a3–5%NaOH–Na2CO3 solution, thenwith a 3%HCl solution containing an inhibitor, and finallywith a 1–2% Na2CO3 solution at the boilingtemperature.
The heating surfaces of the evaporators thatcome in contact with the juice in the first andsecond effects are susceptible to corrosion. Cor-rosion occurs only occasionally, but to a verygreat extent. The causes of corrosion are dis-puted [127]. It is, in all probability, largely acidcorrosion, which is favored by the fact that theoxide layers formed are constantly peeled off bythe complexing agents (malic and citric acids)present in the juice. Acid corrosion can also becaused by the release of sulfur dioxide addedto the thin juice in the vapor bubbles for a shorttime during evaporation.Alternatively, themetalmay be attacked by an increased hydrogen-ionactivity resulting from a decrease in pH of thejuice by ca. 1.0–1.5 units at higher temperature[128]. Thus, the pH of thin juice should be kepthigh enough that the pH values of the thick juicedo not fall below 8.8, measured at 20 ◦C. Thethick juice is filtered before further processing.
Sugar 33
10. Production of Sugar from ThickJuice
In the sugarhouse, sugar is produced from thethick juice obtained by the evaporation of thinjuice. This involves crystallization (recovery ofmassecuite magmas) and separation of the sugarfrom the mother syrup (centrifugation). Bothcrystallization and separation of the sugar mustbe carried out in several steps because the tech-nically achievable degree of desugarization ina single crystallization is limited by the maxi-mum amount of crystals (50–60% yield) in themagma (i.e., crystal mass) permitted for ade-quate movement and the increase in nonsugarsubstances in the mother syrup.
10.1. Production of Massecuite
From the thick juice (solids content = 68–74%,sugar content = 61–70%, nonsugar content =4–7%), multistage crystallization produces 85–92% of crystalline sucrose without the useof ion-exchange processes or other molassesdesugarization methods. The rest of the thickjuice sugar (8–15%) and practically all of thenonsugar substances in the thick juice are foundin molasses, the mother syrup of the last crystal-lization (solids content = 84–89%, sugar con-tent = 50–56%, nonsugar content = 32–40%).If inclusion of mother syrup in the crystal andimperfections of the surface are prevented by op-timal crystallization techniques, more than 99%of all the ionogenic nonsugar substances and ca.95% of all the highmolecular mass and surface-active nonsugar substances, including colorants,remain in themother syrup after each crystalliza-tion step.
The syrups (thick juices, remelts) can besimplified regarded as three-component systemsconsisting of sugar, nonsugars, and water. If pre-cipitation crystallizationwith organic solvents isdisregarded, two methods are available theoret-ically for the industrial-scale crystallization ofsucrose. Both methods are used in practice.
1) Evaporating crystallization (→ Evaporation,Chap. 6, → Evaporation, Chap. 7) is per-formed either isobarically or isothermally.With pure syrups, the sugar–water ratio in themother syrup remains approximately constant
during evaporating crystallization. With im-pure syrups ( p < 90), however, this ratio in-creases because the amount of nonsugars inthe mother syrup increases significantly dur-ing crystallization. Therefore, the solubility-increasing effect of the nonsugar substancesalso increases greatly. The solids content ofthemagma increases during evaporating crys-tallization.
2) Cooling crystallization is based on the de-crease in solubility of sucrose with decreas-ing temperature (see Table 2). The remainingsucrose concentration in the mother syrup es-sentially follows the saturation line in the caseof pure sugar solutions. In less pure industrialsugar solutions (p < 85, see Section 5), thesolubility of sucrose in the mother syrup isconsiderably increased. In pure cooling crys-tallization, the solids content of the magmaand the nonsugars–water ratio in the mothersyrup remain constant. Cooling crystalliza-tion is used only in combination with evap-orating crystallization.
Supersaturation Coefficient, Measure-ment, Control. The rate of cooling or evap-oration during a crystallization process mustbe adjusted to the immediate crystallization rate(→ Crystallization and Precipitation, Chap. 4.2)to prevent secondary nucleation (→ Crystalliza-tion and Precipitation, Chap. 4.1.2) and achievethe most uniform crystal formation and distri-bution. The rate of crystal growth is controlledmainly by diffusion. The increase in mass of acrystal per unit time depends on the crystal sur-face [129]; the rate of insertion of the moleculesinto the crystal surface or the diffusion constantof sucrose in the solution [130]; the thickness ofthe diffusion boundary layer, which is between60 and 150 µm [131]; and the supersaturation(Fig. 8). Mass transfer in the magma is influ-enced substantially by flow conditions [132]so that in evaporating crystallization, naturalvapor-bubble mixing is supported by mechani-cal stirring [133].
The sucrose concentration is normally repre-sented by the supersaturation coefficient c1. Thisrefers to the quotient
c1 =c
cx
34 Sugar
where c is the sugar content of the solution inquestion and cx the saturation concentration ofsugar in the solution at the same temperature.
The range c1 = 1.0–1.2 is called metastable.In this range, only crystals that are alreadypresent can grow; no newcrystals can be formed.In the intermediate saturation range c1 = 1.2–1.3, however, crystal formation can be causedby shock (air, impact, etc.). In the labile rangeabove c1≥1.3, crystal nuclei are formed sponta-neously. Maintaining the proper supersaturationcoefficient is of great importance for practicalcrystallization. Since no direct method exists forcontinuous measurement of the supersaturationcoefficient, it must be determined by indirectmethods. The following parameters are suitablefor this purpose: measurement of the electricalconductance, measurement of the boiling-pointelevation, determination of viscosity or consis-tency [134], shifting of the oscillator circuit ofradio-frequency sources [135] (frequency range6–150 MHz), determination of the total solidscontent (e.g., radiometrically [136] or by high-frequency ultrasonic vibrations), and refracto-metric measurement of the solids content of themother syrup [137]. Measurements of the vis-cosity or consistency of the magma (stirrabilitymeasurement [134]), total solids content of themagma [136], and density of the mother syruphave proved useful as guiding values for the en-tire crystallization process [137].
Attempts have been made to control crystal-lization via on-line measurement of the crystal-size distributionwith the help of laser-diffractionspectrometers.
10.2. Evaporating Crystallization
Batchwise Process. Evaporating crystal-lization is carried out mostly batchwise in pansat 20–30 kPa and a massecuite temperature of65–80 ◦C. The process can be divided into foursections [138]:
1) A quantity of syrup to be boiled is drawn intothe pan so that the heating chamber remainscovered during thickening of the syrup. Thesyrup is then evaporated to a supersaturationcoefficient c1 of 1.0–1.2.
2) A known number of crystals in the formof microcrystals (d ′ = 10–20 µm, n ≈ 2, sus-pended in 2-propanol) or seed magma (d ′ =
180–250 µm, n ≈ 3.0) are added to the syrup.The grain-size distribution of sugar crystalsfollows the Rosin–Rammler–Sperling dis-tribution, n is a parameter of the Rosin–Rammler–Sperling distribution; high n indi-cates uniform grain size (→ Elutriation).When working with microcrystals, the num-ber of crystals added must be larger than thedesired number of crystals in the entiremasse-cuite in the pan at the end of sugar boiling. Thereason for this is that part of the crystal nucleidissolves because of the varying temperatureand supersaturation conditions in individualtubing sections of the heating chamber. Table8 lists the number of total surface of the crys-tals contained in 1 kg of sugar as a function ofcrystal size [139]. Until crystals become vis-ible to the naked eye (interfacial length of ca.50 µm), the supersaturation coefficient mustbe kept at about the same level. During thistime, only small amounts of sugar crystal-lize, but the movement of massecuite mustbe maintained by means of water evaporationor mechanical stirring. For this reason, waterinstead of syrup is drawn into the pan in thisphase. Since this type of “crystal seeding” re-sults in a higher energy requirement, is tech-nologically difficult to control, and is moretime consuming, a seed magma has becomethe crystal seed of choice. This seedmagma isproduced separately by evaporating–coolingcrystallization in a process similar to the onedescribed here [140]. The mass of the crys-tal magma charge increases by a factor of 103
(30–50 kg of seedmagma per tonne ofmasse-cuite in the pan). This mode of operation al-lows the use of feed syrups of higher con-centration (e.g., thick juice and liquor witha solids content of 72–74%; for details onliquor, see Section 13.2).
Table 8. Number and total surface area of crystals in 1 kg of sugaras a function of crystal size [119]Size of crystals* Ls Number of sugar crystals
3) In the following phase, the crystals shouldgrow to their final size without formation ofnew crystals (secondary nuclei) or conglom-eration of the crystals present (agglomeratedgrain). To work at high supersaturations and,consequently, high rates of crystallization, thelayer thickness λ (i.e., half the space bet-ween two crystals) must be less than 0.25mm at the start and about 0.1 mm at the endof crystallization (layer thickness λ = volumeof mother syrup in cubic meters per surfaceof sugar crystals in square meters). In addi-tion, adequate circulation must be maintainedwithin the massecuite in the pan. Therefore,natural vapor-bubble mixing is being increas-ingly supported by mechanical stirring [133].The continuous or periodic feeding of juiceand the rate of evaporation should bemutuallyadjusted in such a way that the requirementsmentioned above are largely fulfilled. Controlvalues here are indirect supersaturation mea-surements and the level in the pan.
4) Finally, the massecuite in the pan is concen-trated to the proper consistency (crystal con-tent 50–60%) for centrifuge work. The solidscontent at the end of the crystallization pro-cess is 89–91% in the case of “white” masse-cuites (refined massecuites, see Section 13.2,white sugar 2, raw sugar 1) and 92–96% in thecase of “brown” massecuites (i.e., raw sugar-2 and after-product massecuites, see Section13.2).The flowability of themagmas depends on theviscosity of the mother syrup (solids content,temperature, pH); crystal content; crystal-sizedistribution; and crystal form [141]. For thisreason, only approximate values for theflowa-bility of magmas can be given. The “viscos-ity” of refined massecuites is between 50 and100 Pa · s, of white sugar massecuites bet-ween 90 and 170 Pa · s, of raw sugar-2masse-cuites between 300 and 800 Pa · s, and ofafter-product massecuites between 500 and2000 Pa · s. The end point of sugar boiling isdetermined by the consistency of the magma.
Despite batchwise operation, the technologi-cal course of the process is automated to a largeextent [142]. A pan holds a maximum of 120t of massecuite; the installed heating surface insquare meters is about 45–60% of the masse-cuite content in 100 kg (i.e., 200–300 m2 calan-
dria surface for a 50 t pan). The calandria are ei-ther tubular (brass or steel tubeswith an inner di-ameter of 95 mm) or ring or hexagonally swagedcalandria tubes with about 50 mm of clear spacebetween two walls. To permit good circulationof the massecuite in the pan, a central tube islocated in the middle of the calandria (e.g., forwelded tubular and ring heating chambers), or anannular space is present at the outer edge e.g.,for suspended calandria (dished floating calan-dria). In calandria with a central tube, additionalcirculation is possible viamechanical stirring. Inthis case, the massecuite is pushed through thecentral tube into the space below the calandriaby a slowly operating mixer (60–80 rpm) [133].The vacuum required (15–25 kPa) for boiling isproduced as described in Chapter 9.
Continuous Process. Intensive efforts haveenabled continuous evaporating crystallizationto be developed into a controllable processon the condition that about 25% of the seedmagma (based on finishedmassecuite) producedbatchwise is fed continuously into the process.New plants in industrialized countries, espe-cially for “brown” massecuites (raw sugar 2,after-product), are installed as continuous plants[90, 129, 143].
Two types of equipment exist: horizontal andvertical. In horizontal equipment, the total crys-tallization distance can be divided without prob-lem into several compartments (stirred-tank cas-cades, n < 12). With vertical crystallizers, acompromise must be made between the techno-logical requirement for a good residence-timedistribution (i.e., more than six compartments)and equipment costs. For this reason, verticalcrystallizers usually consist of only four stirredtanks.
The individual process steps described abovefor batchwise crystallization are carried out oneafter another in a continuous process, spatiallyseparated in individual compartments. This hasboth advantages and disadvantages. Thus, acrystal size distribution (n > 3.0) as good asthat in batchwise operation has not yet beenachieved because secondary crystal formation inindividual compartments cannot be prevented.Unlike the batchwise process, secondary crys-tals cannot be redissolved, if necessary, by di-luting the mother syrup (attainment of subsatu-ration) [144].
36 Sugar
The advantages of continuous crystallizationare as follows:
1) The temperature difference between heatingsteam and magma is smaller because themassecuite level is low, which makes use oflow-pressure steam possible [145].
2) Individual compartments are easier to con-trol. Continuous boiling equipment is usu-ally operated isobarically. For vertical equip-ment, however, various vapor pressure stepsare employed in individual chambers. In thisway, evaporating–cooling crystallization isachieved (flash evaporation) [146].
Easy scaling of the equipment at the interfaceof magma–vapor space, especially in the case ofwhite massecuites, is a problem that has not yetbeen solved [147].
10.3. Mixing of Massecuites and CoolingCrystallization
After the completion of evaporative crystalliza-tion, the massecuites are stirred continuously inmixers/crystallizers until the sugar is centrifugedoff. This prevents separation of the crystal massfrom themother syrup by sedimentation. Inmix-ing white massecuite, the temperature is usuallyheld constant. Temperature changes, especiallyat thewalls, must be avoided because of possiblesecondary nucleation and conglomerate forma-tion.
Cooling Crystallization. Controlled cool-ing of the massecuite in the crystallizer dur-ing the mixing process (cooling crystalliza-tion) is generally employed for after-productmassecuites (see Section 13.2) and is used onlyoccasionally for raw sugar-2 and white sugarmassecuites [148]. The advantages that can beachieved from a technological and heat econ-omy point of view are so great that coolingcrystallization will definitely be introduced inthe near future for raw sugar-2 and white sugarmassecuites [149].
In the case of after-product massecuites,about 85% of the sugar crystal mass is producedby evaporating crystallization and the remain-der by cooling crystallization. In cooling crys-tallization, the massecuite in the crystallizer is
cooled by 0.5–1.5 ◦C/h from ca. 65 ◦C to 35–40 ◦Cwith constant stirring. This results in cool-ing crystallization times of 36–40 h. The crys-tallizers (→ Glucose and Glucose-ContainingSyrups) used for cooling are horizontal U-shaped vessels or horizontal or vertical cylin-drical vessels in which rotating or stationarycooling elements (≈ 1.5–2.5 m2/m3 crystallizervolume) are installed. Thermostated water flowsthrough these elements (temperature differencebetween the water and the massecuite in thecrystallizer < 15 ◦C). To lower the consistency,which increases with decreasing temperatures,water or syrup must be added to the massecuiteduring cooling in an amount that prevents themagma viscosity from rising above 3000 Pa · s.
An increase in consistency of the massecuitein the crystallizer can also be prevented by firstcooling the massecuite only by 10–15 ◦C. Partof the massecuite (ca. 20%) is then centrifuged.The centrifugedmother syrup is reheated, deaer-ated, and returned to the magma. In this manner,the crystal content of the magma is lowered byabout 7%. The crystal content increases againduring further cooling, without the massecuiteconsistency increasing in an uncontrollable way.This mode of processing leads to a decrease inpurity of 2–3 units in the molasses and, thus,higher sugar yields [150].
Cooling crystallization of other massecuitesin the crystallizer, such as white sugar and rawsugar, is carried out in similarly designed crys-tallizers. Cooling rates up to 8 ◦C/h are possi-ble, depending on product purity. The installedcooling surface per cubic meter of crystallizervolume is between 2.5 and 5 m2. The temper-ature difference between cooling medium andmassecuite in the crystallizer should not exceed5 ◦C because of possible secondary nucleationat cooling surfaces.
10.4. Factors That Influence Rate ofCrystallization
The rate of crystallizationof sucrose is expressedas mass growth rate G (g m−2 min−1) or as lin-ear growth rate LG (µm/min), both related byG = 0.711×LG [139]. The growth rate dependsprimarily on purity, temperature, and supersatu-ration (Fig. 8) [151]. Under otherwise identical
Sugar 37
conditions, the rate is reduced by high molecu-larmass substances (e.g., dextrans), colored sub-stances (e.g.,Maillard products), and also by raf-finose, kestoses, etc. [152]. A raffinose concen-tration greater than 1% (based onmagma solids)causes a marked decrease in the rate of crys-tallization and the formation of needle-shapedcrystals, which is especially pronounced whencalcium saccharate is returned to the juice pu-rification (Steffen process, see page 50).
These problems can be avoided by cleav-age of raffinose into sucrose and galactosewith α-galactosidases [153]. Raffinose is usu-ally cleaved in the raw sugar-2 green syrup. At-tempts to eliminate the invertase contained, inaddition to α-galactosidase, in the enzyme mix-tures have been successful [154]. Apart fromimproving crystallization work, these processespermit better exhaustion of the molasses. How-ever, the process is profitable only under certainconditions.
11. Separation of Sugar fromMassecuite
Crystallized sugar is recovered from the masse-cuite mostly by batchwise centrifugation inscreen-basket centrifugals [90] (top-suspendedcentrifuges,→ Centrifuges, Filtering). This op-eration – including loading and unloading – isautomated to such an extent that a stationwith several machines works practically contin-uously.
Continuously operated centrifuges, espe-cially continuous conical basket centrifugals,are used only for centrifugation of after-productmassecuites [156] and, to a lesser extent, forraw sugar-2massecuites. In the raw sugar indus-try, pusher centrifugals are also used (→ Cen-trifuges, Filtering). Because of the crystal dam-age occurring in these centrifuges, they are onlypartly suited to centrifugation of consumptionsugar (refined sugar, white sugar).
The first mother syrup obtained on centrifug-ingmassecuite is called “green syrup.”Molassesis obtained in the last crystallization step. For thetheory of the formation and exhaustion of mo-lasses, see [156].
If the sugar is subsequently washed in thecentrifugal with hot water and steam to com-pletely remove syrup particles adhering to the
sugar crystals, a “wash syrup” is obtained. Thiswashing is required in the production of con-sumption sugar (white, refined) and in the affina-tion (washing the crystal surface free of mothersyrup) of raw and after-product sugars (see Sec-tion 13.1). The wash syrup is generally col-lected separately. However, the wash syrup andthe green syrup cannot be very cleanly sepa-rated. The separation technique was improvedby introduction of a pneumatically controlledcovering device in a BMA centrifugal [157].Separation depends primarily on the purity thatmust be attained in the syrup to maintain theplanned crystallization scheme. About 6–8%(sugar based) of water and steam is requiredfor washing. The water or steam wash must bestarted at the proper time to prevent unneces-sary dissolution of sugar [158]. Before the actualwashingprocess,washing the sugar crystalswithslightly undersaturated sugar syrups of a highertemperature than that of themagma (syrupwash)to be centrifuged represents another measure tominimize the dissolution of sugar in the cen-trifuge.
Double- cone centrifugals are used today forthe affination of brown massecuites, a syrupwash replacing the mixing process. This waspreviously a two-stage process (centrifugationof the mother syrup and remixing of the crystalsin a syrup of higher purity than that of the orig-inal mother syrup; second centrifugation withwashing of the crystals). In these centrifuges,the baskets of two continuous centrifuges areinstalled above each other (Fig. 9).
12. Preparation of Refined andWhite Sugar
Refined and white sugar leave the centrifugeswith a water content of 0.5–1%, depending onthe temperature of the massecuite and washwater and the g attained (maximum 900) dur-ing spinning. Surface water content must be re-duced to 0.03–0.05% before further processing.For this purpose, hot-air heaters, cocurrently orcountercurrently operating drum dryers (gran-ulators), trickle-bed towers, turbo-tray dryers(→ Drying of Solid Materials, Chap. 2.1.2), orfluidized-bed dryers (→ Drying of Solid Mate-rials) are used. The sugar can be cooled beforeit is discharged.
38 Sugar
Figure 9. Double continuous centrifuge type SC 1350/1500 ODSa) Motor; b) Bearing; c) Bridge girder; d) Basket shaft; e) Basket I; f ) Basket II; g) Out-of-balance limiter; h) Enclosure top;i) Enclosure substructure; j) Enclosure cover; k) Service coverwith inspection glass; l) Water washing system;m) Steamwash-ing system; n) Thick-juice washing system for basket II; o) First molasses runoff; p) Mash runoff (affination runoff ); q) Washsyrup runoff; r) Liquor runoff; s) Cascades; t) Runoff separation; u) Sample removal; v) Transport safeguard; w) Automaticoscillation controller; x) Automatic vibration controller
The next step is screening in vibrators orscreening machines (→ Screening) in which thesugar crystals, lumps of > 2 mm, and finesof < 0.25 mm (which are redissolved to giveremelt/liquor) are separated. In factories, all thepreclassified sugar is stored in large- capacity si-los without further separation or it is screenedinto individual fractions (e.g., size fractions 1.2–2 mm = coarse, 0.8–1.2 mm = medium, 0.25–0.8 mm = fine), and sometimes packed for sale.
In some cases, the medium-grain fraction isground in a mill, and a 0.25–0.75-mm fraction
is screened out (ground sugar). Coarse-grainedsugar is usedmainly in industry and fine-grainedsugar is household sugar.
13. Working Schemes of VariousSugar Factories [149, 159]
Figures 10 and 11 present the crystallization andseparation stages in beet sugar factorieswith dif-ferent production programs. The starting mate-rial is thick juice of the same purity, solids con-
Sugar 39
Figure 10. Crystallization schemat-ic of a raw sugar factory withtwo-product operation (quantities inkilograms per 100 kg of beets)
40 Sugar
Figure 11. Crystallization schematic of a white sugar factory (quantities in kilograms per 100 kg of beets)
Sugar 41
tent, and mass in percent (beet based). For a bet-ter comparison, the sugar loss in the molasseswas assumed to be the same in all variations. Thetotalmass ofmassecuites to be processed and themass of water to be theoretically evaporated arelisted in Table 9 for different modes of opera-tion. However, the water mass to be evaporateddoes not take into account the additional waterutilized for crystallization (see Section 10.3) andthe energy requirement for heating the media tobe boiled.
Table 9. Total mass of massecuites processed and mass of waterevaporated in various modes of operation*Mode of operation Amount of
massecuite,kg/100 kgbeets
Theoreticalamount ofwater to beevaporated inthesugarhouse,kg/100 kgbeets
Raw sugar factory with two-productoperation (see Fig. 10)
≈28 ≈7.5
White sugar factory with standardliquor process (see Fig. 11)
≈60 ≈13.5
White sugar factory with 50%refined sugar production
≈70 ≈19.0
Sugar factory with 100% refinedsugar production
≈77 ≈21.0
* The numbers change when other amounts of sugar or nonsugarenter the sugarhouse with the thick juice.
13.1. Operation of a Raw Sugar Factory
At first, beet sugar factories were all raw sugarfactories, as are most cane sugar factories to thisday. The raw sugar produced is processed furtherto white sugar in refineries.
In the refinery (see Section 13.4) raw sugaris again mixed with a mother syrup ( p = 85–89, solids content 75%) to give a magma, cen-trifuged, andwashedwithwater and steam to ob-tain consumption (affinated) sugar as the imme-diate product. Alternatively, the affinated sugaris dissolved to give a remelt syrup and subse-quently boiled to refined sugar.
Raw sugar factories are operated in accor-dance with the two-product scheme (Fig. 10).The raw sugar-1 massecuite in the pan is boiledfrom thick juice with the return of 15–20% ofraw sugar-1 green syrup ( p = 78–80); the runoffsyrup is drawn into the vacuum pan only atthe end of the boiling process. At discharge,the solids content of the massecuite in the pan
is 94%, and the temperature is ca. 74 ◦C. Themassecuite is cooled to 50–60 ◦C by stirring forseveral hours in mixers while more raw sugar-1green syrup is added. The purity of the mothersyrup is reduced from an initial 82–84% to 78–80%. In a second crystallization stage, after-product massecuite is made from raw sugar-1green syrup that is not returned. After-productmassecuite is separated into after-product andmolasses.
The raw sugar (raw sugar 1: pol =95–98◦Z, organic nonsugar = 0.7–1.2%, in-organic nonsugar = 0.8–1.0%, water = 1–2%;after-product sugar: pol = 90–92◦Z, organicnonsugar = 3–4%, inorganic nonsugar = 1.5–2.5%, water = 2–3%) obtained in a beet rawsugar factory has a light-yellow to dark-brownappearance because of the adhering syrup film.It must be made alkaline (prevention of inver-sion and formation of colorants) to be storablefor longer periods.
Beet raw sugar is not suitable for consump-tion because of its unpleasant taste and its saltcontent. However, cane raw sugar (see Section20.6) can be used directly in the production ofgingerbread, fruit cake, etc., because of its aro-matic flavor and taste components. Raw sugarhas no nutritional physiological advantages overwhite sugar.
13.2. Operation of a White SugarFactory – Standard Liquor Process
The schematic of crystallization of a whitesugar factory operating according to the stan-dard liquor process is shown in Figure 11. Thewhite sugar-2massecuite in the pan ismade fromthick juice by the addition of white sugar-2 washsyrup and remelt syrup (explained below) fromaffinated raw sugar 2. In some cases, the affi-nated raw or after-product sugar is dissolved di-rectly in thick juice. Boiling a white sugar striketakes about 2–4 h. The crystal yield is 45–55%,and the solids content at discharge is 90–92%.
Remelt syrup (solids content = 68–72%) is asolution obtained by dissolving affinated rawsugar 2 and after-product sugar (see below). It ispurified of color and high molecular mass non-sugar substances ( p > 99.5%) by activated car-bon or ion-exchange resins. This syrup is heatedto 88–95 ◦C and filtered hot. Ceramic or cloth-
RGC
Resaltado
42 Sugar
covered tube filters precoated with a filter aid(silica gel and cellulose) are used for filtration.
The raw sugar-2 massecuite in the pan is sub-sequently boiled fromwhite sugar-2 green syrup( p = 87–89%) and raw sugar-2 wash syrup ( p= 85–88%). In some cases, affinated or unaffi-nated after-product sugar is used as seedmagma.In this case, “seed magma” refers to the after-product sugar suspended in diluted raw sugar-2green syrup after heating and deaeration to givea massecuite in the crystallizer. Since the after-product sugar has an average crystal size (d ′ =150–250 µm, n>3), the crystals introduced inthis way grow further to 0.6–1.0 mm. Return ofthe after-product sugar as “seed magma” for theraw sugar-2 massecuite in the pan gives a rawsugar-2 product that has a more uniform grainsize and, thus, can be affinated more easily. Re-turn of unaffinated after-product sugar results inconstant recycling of about 10–15% of the en-tire nonsugar substances between after- and rawsugar-2 massecuite.
Raw sugar-2massecuites in the pan are thick-ened to a solids content of 92–93%, the boilingtime being 3–6 h and the crystal yield 48–53%.As mentioned above, the raw sugar 2 obtainedis added directly to the white sugar boiling viathe thick juice or in the form of remelt syrup.
From the green syrup of raw sugar-2 masse-cuite and the wash syrup of after-product masse-cuite, after-product massecuite in the pan is ob-tained, which has a boiling time of 10–20 h be-cause of the low purity of the syrup to be boiled( p = 78–80%) and the resulting low crystalliza-tion rate (ca. 700 mgof sugar per squaremeter ofcrystal surface per minute). If ion-exchange pro-cesses (see Section 14.2) are used to attain a bet-ter sugar yield, the raw sugar-2 green syrupmusthave a purity of p < 75%. The solids content atdischarge of the massecuite is 93.5–95.5%; thepurity in the mother syrup is 62–65%, or 50–55% if ion-exchange processes are used. As aresult of subsequent cooling crystallization, thepurity of the mother syrup, the molasses, de-creases to 59–62%or, if ion-exchange processesare used, 48–53%. The crystal yield from after-product massecuites is 45–49%.
After-product affination is shown in thescheme as if it occurs in the same centrifuge asseparation of molasses. For the operation of affi-nation, see Section 13.1. This additional processis one reason for returning the unaffinated after-
product sugar as seed magma for raw sugar-2massecuite in the pan (see above).
13.3. White Sugar Factories with aRefinery Scheme
In white sugar factories with the crystallizationscheme of a refinery, all the thick juice obtainedis first boiled to raw sugar 1. This eliminates anyinfluences on quality exerted by the nature ofthe thick juice. The raw sugar is washed withonly a little water and then (while raw sugar2 is returned) dissolved to give a remelt syrup,from which the first refined-sugar massecuite isboiled. The resulting mother syrup yields a sec-ond refined-sugar massecuite.
Themother syrup of the second refined-sugarmassecuite is, together with thewash syrup, pro-cessed to white sugar massecuite in the pan.The last two boiling stages correspond to thoseshown in Figure 11. Thus, it is possible to obtain80% of the white sugar production as refinedsugar with five crystallization steps.
13.4. Refining
The working scheme of a refinery correspondslargely to that described above, the differencebeing that the rawmaterial is “foreign raw sugar”instead of thick juice. The processing of beetraw sugar (see Section 13.1) involves only pu-rification of the remelt syrup with the help ofbone charcoal, activated carbon, and decoloriz-ing resins before the boiling process. The pro-cessing of cane raw sugar (see Section 20.6)requires a chemical purification step because ofthe greater content of impurities (especially dex-trans). For this purpose, the remelt syrup mustbe diluted to a solids content of 50–60% andsubjected to juice purification with either phos-phoric acid–phosphates and CaO, or CaO andCO2 (see Section 20.8).
14. Ion - Exchange Processes in theSugar Industry [160]
Ion-exchange processes can be used to increasesugar yield or improve sugar quality (→ Ion
Sugar 43
Exchangers, Chap. 12.1). As early as 1843,Hochstetter proposed that alkali salts of thebeet contribute to the formation ofmolasses. Be-cause of these salts, ca. 11–15% of the sugarintroduced with the beet cannot be obtained inthe crystalline state. For molasses formation andexhaustion, see [156]. At the turn of the century,efforts were made to increase sugar yield by ex-changing alkali ions for less molasses-formingalkaline-earth ions with zeolites or other inor-ganic ion exchangers [161]. However, only afterthe development of ion exchangers basedon syn-thetic resins were ion-exchange processes ap-plied on a large scale.
Ion-exchange processes are used primarilyfor
1) Softening thin juices by exchanging alkaline-earth ions for alkali ions to prevent incrusta-tion during evaporation
2) Increasing sugar yield bya) Replacing alkali ions of the raw sugar-2
green syrup by Mg ions (Quentin process)b) Chromatographic separation (→ Ion Ex-
changers) of molasses into sugar and non-sugar fraction
3) Decolorization of remelt syrups, thick andthin juices
4) Production of liquid sugar (see Section 15.8)
Ion-exchange resins used in the productionprocess must comply with food regulations indifferent countries.
Processes used to increase sugar yield by re-moving ionogenic nonsugar substances (com-plete deionization) have not achieved impor-tance.
When ion exchangers are applied in sucrose-containing solutions, the fact should be notedthat strongly acidic cation exchangers in the H+
form catalyze the hydrolysis of sucrose [162].The total inversion (heterogeneous, homoge-neous), in the case of a thin juice (solids content= 17%, pol = 15.8◦Z, p = 93.0%) and a contacttime of 4 min, is 0.07%at 14 ◦C; 0.2%at 17 ◦C;and 1.5% at 23 ◦C (based on sucrose).
Monosaccharides (glucose, fructose, etc.)and reducing disaccharides are isomerized and,at high temperature, partly degraded to acidsby strongly basic anion exchangers in the OH−form [163].
14.1. Softening of Thin Juice
The ion-exchange process most frequently usedin the sugar industry is the thin-juice softeningprocess at 60–85 ◦C. Since the equivalent ra-tio (Ca2+, Mg2+) : (K+, Na+) in thin juices tobe softened is ca. 1 : 15–1 : 25 – compared with,for example, 2 : 1 in water softening – only asmall operating capacity (→ Ion Exchangers) isachieved (ca. 70–80%). For removal of 1 kg ofCaO from the juice, 7–11 kg of NaCl must beused as regenerant.
To avoid accumulation of regenerant waste-water, softening plants are sometimes regener-ated with diluted raw sugar-2 green syrup con-taining ca. 1 mol/L alkali ions (Gryllus pro-cess [164]) or directly with 1 mol/L sodium hy-droxide (Akzo process [165]), the regenerationrunoff being returned in front of the first carbon-ation. Softening of thin juice with weak cationexchangers in the acidic form and regenerationof the exchangerswith sulfuric acid [166] has de-veloped to an important wastewater saving pro-cess, because the regeneration effluents can beused as a pressing aid in beet extraction and pulppressing.
14.2. Exchange of Alkali Ions forAlkaline - Earth Ions
The sugar yield can be increased by 0.4 to 0.8%(beet based) by exchanging30–50%of the alkaliions in the syrup for alkaline-earth ions. Sincealkaline-earth salts are more hydrated per equiv-alent in aqueous sugar solutions than the corre-sponding alkali salts, they bind more water inthe mother syrup of the last crystallization thanalkali salts. Thus, less solution water is availablefor the sucrose. The molasses obtained after ex-change can achieve a purity of less than 50%,compared to 60% for normal alkali molasses.
Quentin Process. The Quentin process[167] was used widely in the beet sugar industryas long as wastewater pollution was of lowerimportance compared to sugar yield. In thisprocess, alkali ions in raw sugar-2 green syrupare replaced by magnesium ions. The runoffis diluted to a solids content of 68–70% andpassed at 85–90 ◦C over a strongly acidic cation
44 Sugar
exchanger loadedwithmagnesium ions as coun-terion. Since only about 2–3 m3 of runoff can betreated per cubic meter of resin in one operationcycle, the difficulty here is to “sweeten” (i.e.,displace water from the resin bed with syrup)and “desweeten” (i.e., displace syrup from theresin bed with water) in such a way that theamounts of water used are just sufficient to di-lute the runoff from 78 to 70% solids content.Direct exchange of alkali ions for magnesiumions is possible in this case because the ionicconcentration in the runoff is ca. 1 mol/L andthe osmotic pressure in the surrounding liq-uid is very high. Consequently, the selectivityof the ion exchanger for divalent ions is largelycounteracted. The exchanger is regeneratedwithdilute magnesium chloride solution.
14.3. Separation of Molasses into Sugarand Nonsugar Fractions (Ion Exclusion)[168]
At the same time as large-scale processes weredeveloped for separation of glucose–fructosemixtures (invert sugar, HFCS, → Enzymes,Chap. 5.2.3.2.7), efforts were made to isolatesugar from molasses by using ion exclusion (→Ion Exchangers). In 1994, several large-scaleplants with a separation efficiency of 250 t ofmolasses per day were in operation (columnsup to 3.0 m, separation path up to 32 m, batch-wise or continuous, simulated moving-bed pro-cess, ion-exchange resin in Na+ or Ca2+ form).The importance of the ion exclusion process hasgrown rapidly, and in 1997 about 80%of themo-lasses in the US beet sugar industry were treatedin this way [169].
Molasses diluted to a solids content of 60%is separated at 80 ◦C into a sugar (solids content20–30%, p = 89–92%) and a nonsugar fraction(solids content 4–6%, p < 20%) with water asthe eluent. The fractions are evaporated in sev-eral stages to a solids content of 70%. The sugarfraction is crystallized like thick juice, and thenonsugar fraction is processed as cattle feed.
Table 10 shows the extent towhich individualclasses of substances are divided among sugarand nonsugar fractions. With this process, up to80% of the molasses sugar can be obtained aswhite sugar, about 10% goes into the nonsugar
fraction, and the remaining 10% is contained inthe secondary molasses.
The overall sugar recovery was improved byintroduction of the “Coupled Loop” separation[170] or the two-profile FAST technology [171].Today (2005) equipment for separation of mo-lasses into more than two fractions is being in-stalled in the factories, andmainly betaine is iso-lated as a second fraction besides sugar [172].
14.4. Decolorization of Remelt Syrupsand Thin Juices
Instead of treatment with activated carbon,remelt syrups and thin juices can be treated withstrongly basic macroporous anion exchangers inthe chloride form at 80–85 ◦C. The volume ofremelt syrup treated in one operating cycle is200–300 times the resin volume, depending onthe purity of the solution to be decolorized.Witha specific hourly load of 2–3 volumes of remeltsyrup per volume of resin, an initial decoloriza-tion of 90% is achieved; this is reduced to 50%with increasing running time. The average de-colorization attained is 75–80%. Neutral or al-kaline (pH 12–13) 10% sodium chloride solu-tions are used to regenerate the ion exchanger.About 100–150 kg of NaCl is required per cubicmeter of resin [173].
14.5. Elimination of Ionogenic NonsugarSubstances
Acidic Deionizing Process [174]. Thinjuice (solids content = 15–17%) cooled to atleast 14 ◦C, or runoff or molasses diluted to30–40% solids content, is passed first over astrongly acidic cation exchanger in the H+ formand then over a weakly basic anion exchanger intheOH− form. The cations, amino acids, and be-taine are adsorbed on the cation exchanger, andnitrogen-free anions and pyrrolidonecarboxylicacid on the anion exchanger.
To prevent ion slippage as far as possible, twopairs of ion exchangers are connected in series.
The acidic deionization process eliminatesca. 85% of all nonsugar substances. Thin juiceswith a purity of 97–99% are obtained. Sugaryield can be increased to a maximum of 1.2–1.4% (beet based).
Sugar 45
Table 10. Division of individual classes of substances between sugar and nonsugar fractions
Apart from acidic deionization, other partialand complete deionization processes have beendeveloped to prevent the hydrolysis of sucrose.These include the exchange of alkali ions forNH+
4 ions plus the exchange of anions in thejuice for HCO−3 –CO2−
3 ions, and subsequentdistillation of (NH4)2CO3; or the exchange ofanions for OH− ions with a strongly basic ex-changer, followed by elimination of alkali ionswith a weakly acidic cation exchanger.
14.6. Production of Liquid Sugar [175]
Crystalline sugar is dissolved to give a syrupwith a solids content of 50–60%. The syrupis filtered through a depth filter (→ Filtration,Chap. 4), decolorized at 80 ◦C, and then deion-ized completely at 20–40 ◦C. For the productionof invert sugar syrups, an inversion resin (cationexchanger in the H+ form) is integrated into thedeionization path. The desired degree of inver-sion is attained by variation of temperature andresidence time.
The syrup leaving the ion-exchange facilityis finally evaporated in several stages to a solidscontent of 65–75%. Facilities are sized to re-quire regeneration only after 120–150 h.
15. Production of Special Types ofSugar
15.1. Cube Sugar
The invention of cube sugar dates back to 1843.Today two different processes are applied in theproduction of cube sugar: the poured cube pro-cess (Adant process) and the pressed cube pro-cess.
Poured Cube Process. In the Adant pro-cess, the cube massecuite with a temperatureof 98–100 ◦C is filled into the baskets of spe-cial centrifuges in which it solidifies on cool-ing (12 h) to give slabs. The baskets are thenplaced in centrifugals; the adhering green syrupis centrifuged off; the sugar slabs are washedwith wash syrup (i.e., a saturated pure sugar so-lution) and centrifuged dry. Slabs containing 2–3% moisture are dried in drying chambers orchannels and then cut into strips with saw bladesin special machines. Subsequently, the strips arebroken into cubes in clipping machines and usu-ally packed loose. Since cube yield is poor (ca.80% based on dried slabs) and production isboth cumbersome and labor intensive (ca. 500working minutes per tonne of cubes in largeplants), poured cubes are seldom produced inindustrialized countries.
Pressed (Molded) Cube Process. In thepressed (molded) cube process, crystal sugarwith a certain grain size (e.g., 0.4–0.8 mm) anda relative density of 0.82–0.84 is moistened ina mixing screw with 1.5–1.8% of water. It issubsequently pressed into cubes by means ofpresses (Machines Chambon, Paris [176]) or byvibration in vibration forming machines (SSA-Process) [177]. The individual cubes are dried incontinuous drying ovenswith hot air or on a steelband by high-frequency heating. They are thencooled and packed immediately in an arrangedmanner. The hardness of the cubes producedand, thus, their mechanical stability as well asrate of breakdown (dissolution) are substantiallyinfluenced by parameters such as grain-size dis-tribution of the sugar used, water content in themixing path, forming pressure, and drying rate[178].
46 Sugar
15.2. Sugarloafs and Sugar Cones
Sugar cones (sugarloafs) have only regional andseasonal importance (burnt punch). Like cubesugar, they can be made by using the pouringor pressing process with a loaf or cone forminstead of slabs. In the past, pressing was per-formed exclusively manually. Fully mechanicalplants were developed in the 1960s [179].
15.3. Rock Candy
Rock candy is available as string candy or string-free candy. String candy is made according tothe Stovenmethod. In this process, an especiallypure sugar solution with a solids content of 75–78%is discharged at 95 ◦Cinto tanks containingstrings stretched across them. On cooling, thesugar crystallizes on the strings in large crys-tals. Cooling must occur very slowly (8–9 d) ac-cording to a definite temperature program. The“massecuite” should not be shaken during cool-ing. String-free rock candy can be made by crys-tallization in movement (e.g., in Wulff–Bockcrystallizers) or in other continuous processes(e.g., where seed crystals are placed on screens)[180]. In all these processes, exact maintenanceof temperature, flow rate, concentration, pH ofthe sugar solution, etc., is important. Brown rockcandy is obtained by adding caramel sugar (seeSection 15.9) to the sugar solution.
15.4. Icing Sugar
Icing sugar is made by grinding sugar in impactor hammermills (→ SizeReduction). The grain-size distribution follows the Rosin–Rammler–Sperling distribution (d ′ = 40–60 µm, n = 1.8–2.5). Because of the danger of sugar dust explo-sion [181], icing sugar may be produced onlyif special safety measures are taken (separaterooms with light walls, ceiling, etc.). Icing sugarmust be conditioned carefully (heated, dried toa certain moisture content, and cooled) beforepacking so that it does not become hard duringstorage. No general agreement exists about op-timal conditioning requirements [182].
To prevent hardening of icing sugar, the ad-dition of up to 5% starch or 1.5% anticaking
agents, (e.g., certain calcium phosphates, mag-nesium carbonate, amorphous SiO2) is permit-ted in many countries [183].
15.5. Instant Sugar
Instant sugar dissolves very quickly and is pro-duced fromfinely ground icing sugar by agglom-erating it in a fluidized bed with the addition ofsuperheated steam [184]. The resulting granu-late is fine pored and unevenly formed, and hasa grain size up to 5 mm and a bulk density of0.4 kg/L. In comparison, the bulk density of ic-ing sugar is 0.6 kg/L and that of crystal sugar0.8–0.9 kg/L, depending on grain size.
15.6. Preserving (Jelly) Sugar
Preserving ( jelly) sugar is a preparation of crys-tal sugar, dry pectin, tartaric acid, and/or cit-ric acid: 0.8–1.3% pectin, depending on thejelling strength of pectin (→ Polysaccharides,Chap. 3.4.1), and 0.4–0.7% tartaric acid or 0.6–0.9% citric acid are added to the sugar. Pectinwith a degree of esterification of 48–50% dis-solves completely in a solutionwith a solids con-tent of> 50%and forms a stable gel [185].Ami-dated pectins (→ Polysaccharides, Chap. 3.4.1)are employed for the production of preserving( jelly) sugar, which contains sorbic acid as apreservative and is used in the proportions 1 partof preserving sugar to 2 parts of fruit.
15.7. Brown Sugar (Soft Sugar)
Brown sugar is the general term for crystal sugarthat contains invert sugar (muscovado, browncandy, bastard sugar). This crystal sugar hascolor flavoring and taste components dissolvedmainly in its syrup film (water content≤ 3.5%,total sugar content > 93%, color in solution upto 30 000 ICUMSA units). Soft sugar is pro-duced by directly boiling special sugar syrups,and the sugar centrifuged off is not washed. Al-ternatively, it can bemade bymixingwhite crys-tal sugar with prepared sugar syrups [186].
RGC
Resaltado
RGC
Resaltado
Sugar 47
Figure 12. Beet sugar factorya) Continuous evaporation–crystallization tower; b) Evaporator station; c) Boiler (6 MPa; 515 ◦C)VA = steam boiler- condenser; 1 B = vapor of the 1st step of evaporation.
15.8. Sugar Solutions
The quality, composition, and labeling of sugarsolutions are regulated in the EC [187] and, inpart, in the United States [188].
Accordingly, “liquid sugar” may not containmore than 3%, “invert liquid sugar” not morethan 50%, and invert sugar syrup must containmore than 50%, invert sugar.
Since liquid products can be transported anddistributed easily, and because of their uniformquality from a microbiological viewpoint, sugarsolutions are being used increasingly in manu-facturing. Their share of the market, includinghigh-fructose corn syrup (HFCS) (→ Glucoseand Glucose-Containing Syrups, Chap. 6.2), isca. 45% of total sugar sales in the United Statesand 10–15% in other industrialized countries.
In the production of sugar solutions, whitesugar is dissolved in hot, low-salt drinking wa-ter; the syrup is filtered and sterilized by high-temperature, short-time heat treatment (8 s at138 ◦C). The syrup is then cooled to 15–20 ◦C
and stored almost sterile (plate counts< 200/10g dry substance) before transport. Any contam-ination with microorganisms in the air must beavoided.
Solutions containing invert sugar are pre-pared mainly by the ion-exchange process (seeSection 14.5). However, batchwise or continu-ous acid hydrolysis is also used [189]. On heat-ing to 85 ◦C and acidification with sulfuric acidto pH2.5 (ca. 140 g of sulfuric acid per 100 kg ofsugar solution), an 80% sucrose solution under-goes inversion to ca. 70% in ca. 90 min. To pre-vent further inversion, the pH must be increasedsubsequently with sodium carbonate (pH 4–5).If no further discoloration is to take place, theinverted solution should be cooled quickly. En-zymatic hydrolysis of concentrated sugar solu-tions with the help of immobilized invertases attheir pH optimum of 4.5 (β-fructosidase, E.C.3.2.1.26) is technically possible, but it is eco-nomically inferior to the other processes. In-verted sugar solutions are supplied with a solids
48 Sugar
content up to 75%. The degree of inversionmustbe ca. 0.65 to prevent crystallization of glucoseor sucrose.
15.9. Burnt Sugar and Caramel Colors(Caramels)
Burnt sugar is made by heating (melting)sugar or sugar solutions. It has a typical carameltaste, which deteriorateswith increasing color ofthe product. Burnt sugar is producedwith a colorof up to 18 000 EBC (European brewery colour)units, the caramel taste determining the prod-uct’s value [190].Caramel colors (caramels) aremade from sugar or other edible types of sugarby adding certain permitted burning additives[191]. Caramels can be divided into four groups:caustic, alkali sulfite, ammoniac, and ammoni-um sulfite [192]. Different types of caramel arerequired to color certain foods (e.g., spirits, vine-gar, malt beer, and cola beverages).
16. Storage of White Sugar
Since white sugar factories produce sugar onlyduring the working season (three to six monthsper year), but sugar is consumed year-round,large amounts of the sugar produced must bestored. Consumption sugar is packed in 100-kgjute sacks or in 50-kg (25-kg) paper sacks andstored. Household sugar is packed in the factorydirectly in small packages of 0.5–5 kg.
Sugar should not contain dust or lumps beforestorage. It must be dried to 0.03–0.04% resid-ual moisture and cooled to 20–25 ◦C. Storagein high-capacity silos is becoming increasinglycommon [193] because it enables the delivery ofbulk shipments (rail/trucks) to the manufactur-ing industry. In industrialized countries, industryconsumes approximately two-thirds of the totalsugar sold.
White sugar silos are usually vertical cylin-ders made of steel, prestressed concrete, or sheetsteel and provided with a heatable insulatedjacket [194]. Most of the silos have a capacity of10 000–40 000 t, a diameter of 20–37 m, and asugar head up to 40 m high, but very large siloswith capacities of 80 000 t, diameters of 51 m,and a sugar head up to 60m high were erected in
2000 [195]. Sugar silos are filled and emptied ac-cording to various principles; e.g., they are filledfrom the bottom upward from a central pipewitha screw system and emptied from the top down-ward (N. Weibull, Malmo; ABR, Wiedemann,Sarstedt). In other silos, sugar falls through theentire free height of the silo.Measurements haveshown that fears of dust explosions in this modeof operation (due to sugar dust concentrations)are unjustified [181, 196]. The sugar stored in asilo of this type can be circulated constantly byremoving it from the bottom and transporting itto the top. Thismeasure, together with proper airconditioning (T < 25 ◦C, R.H. < 60%) of thesilo, prevents sugar from caking and/or bindingduring storage. For air conditioning and espe-cially for adjusting the humidity, adsorption andrefrigeration processes are used.
During storage, sugar releases not only mois-ture adhering as a syrupy film to the crystal sur-face, but also part of the bound moisture (in themother syrup enclosed in crystal defects) [197].
High-capacity silos constructed like sugar si-los are used for storage of pelleted dry pulp (seeSection 17.2) [198].
17. Auxiliary Facilities in a SugarFactory
17.1. Steam and Energy Balance
The steam requirement of a sugar factory is metby the production of superheated steam in boil-ers of various types. High-pressure boilers (6.7–10 MPa) are being used increasingly. All or thelargest part of the superheated steam (<537 ◦C)is expanded to 0.25–0.30 MPa via turbogenera-tors (counterpressure machines). The electricalenergy thus produced is largely consumed in thesugar factory itself, and the surplus is transferredto the public grid.
Unlike the process steam requirement, theelectrical energy requirement has increased inthe last years. Consequently, gas turbines arenow set up in front of the boiler plant to meetelectrical energy requirements.
The steam flow, vapor distribution, and con-densate scheme for a white sugar factory aredepicted in Figure 12. The entire condensatefrom the first effect of the evaporator station(b) (steam condensate from the turbines) is used
RGC
Resaltado
Sugar 49
as boiler feedwater. In the case of low-pressureboilers (<4 MPa), condensate from the secondeffect of the evaporator station is used to coverlosses. However, since this condensate can con-tain volatile organic substances [120] and, pos-sibly, traces of sugar, this portion of the wateris replaced by treated water in the case of high-pressure boilers.
Exploitation of the energy of boiler exit gasesfor drying cossettes in the beet sugar factory didnot gain acceptance for decades. Only with theintroduction of oil or gas burners was boiler exitgas at 150–200 ◦C increasingly used as “addi-tional air” for drying pulp. In this mode of op-eration, the oil or gas is burned with a slightexcess of air, and the 1600 ◦C hot burner gasesare cooled subsequently with boiler exit gas tothe required working temperature of the dryingprocess (600–700 ◦C).
Herewith, 93–94% of the usable amount ofheat introduced with the fuel can be utilized,compared to 80–86% in the normal mode ofoperation. For detailed energy balances of theentire factory, see [126].
In contrast to beet sugar factories,whichmustuse fossil fuels for steam generation, the entireenergy requirement of the cane sugar industryis met by burning the bagasse in specially con-structed boilers (see Section 20.5.3). Since thecane industry has taken over time-tested heat-flow schemes for the production process fromthe beet sugar industry, a surplus of bagasse isnow available that can be used elsewhere.
17.2. Drying, Pelletizing, and StoringPulp
Drying. Goodmechanical pressing of the ex-tracted pulp is a precondition for efficient pulpdrying (see Section 7.5). If 5.6 kg of dry pulp(solids content 90%) is obtained from 100 kg ofbeets, the amounts of water listed in Table 11must be evaporated during drying.
The amount of heat required for evaporationof 1 kg of water depends on the temperature gra-dient between the entrance and exit of the drum.The higher the combustion gas temperature atthe entrance of the drum, the greater is the ther-mal efficiency of the plant.However, excessivelyhigh entrance temperatures lead to strong scalingof the internals and burning of the material to be
dried [formation of volatile organic acids, totalamount expressed as total organic carbon (TOC)and CO]. For entrance temperatures of 600 ◦C,ca. 3500 kJ per kilogram of water to be evap-orated must be employed. In the drums, 150–180 kg of water evaporates per hour per cubicmeter of drum contents [199]. Cocurrently op-erated rotary drum dryers with preceding firingare used for drying pressed pulp (→ Drying ofSolid Materials). For measures for the efficientuse of energy in cossette drying and optimal con-trol of cossette drying plants, see [126, 200].
For predrying pressed pulp, low-temperaturedryers have been employed to make use of thelower-energy heat that was previously releasedto the environment. Most of the four-rack beltdryers operate with hot air (≈ 60 ◦C), which isheated with the waste heat carriers’ hot waterand condensate (< 70 ◦C) [201].
Apart from hot-air dryers, steam dryers arenow being used to dry pressed pulp. Drying isachieved with superheated steam:
1) With steam of 130 ◦C,which expands to 102–103 ◦C (≈0.1 MPa) by the uptake of water[202] or
2) With steam of 260 ◦C (ca. 2.6 MPa), whichexpands to 148 ◦C (0.37 MPa) [203]
The advantages of steam dryers are energysaving and the closed design, which preventsescape of gaseous emissions (odors). Besideshigh investment, improvable performance andconsiderable maintenance costs have to be takeninto account as disadvantages [204].
Processes that eliminate water from pressedpulp not by drying, but by multiple-effect evap-oration with the help of an entrainer (e.g., edibleoil, paraffin oil) have not yet gained acceptance(Carver–Greenfield process).
Storage and Transportation. Dried pulphas a bulk density of 200–300 kg/m3. Thus,storage and transportation of this material arevery space consuming. Also, in this form, itis not flowable, is poorly miscible (with othercomponents in the production of mixed feed),and only poorly grindable. For these reasons,dried pulp is for the most part pelletized (8–10-mm diameter, 20–30-mm length) [205] (→Size Enlargement B, D). This increases the bulkdensity to 650–700 kg/m3, and the product can
50 Sugar
Table 11. Amount of water (in kilograms) to be evaporated in the drying of beet pulp as a function of solids content of pressed pulp
Solids content of pressed pulp, %
16 18 20 22 24 26 28 30 32 34 36Based on 100 kg of beets 25.8 22.4 19.6 17.3 15.4 13.8 12.4 11.2 10.2 9.2 8.4Based on 100 kg of dried pulp 462 400 350 309 275 246 221 200 181 165 150
be handled and ground easily. Dried-pulp pel-lets are stored in warehouses and, more recently,in high-capacity silos of up to 30 000 t [198].In these silos, better conditioning of the en-tire space is possible and molding is virtuallyimpossible.
17.3. Lime–Carbon Dioxide
For juice purification, 0.8–2.0% (beet based)of CaO and 4.0% (beet based) of carbonationgas (carbon dioxide content of 42 vol%) are re-quired.Thesematerials are produced in the sugarfactory itself by burning limestone (2–5%, beetbased) in high-performance shaft kilns [206].The quicklime is hydrated with water to formmilk of lime (180–220 g of CaO per liter of wa-ter) and freed of oversize material by means ofvibrating screens, rake classifiers, and hydrocy-clones. To guarantee exact dosing, the densityof the milk of lime is kept constant. Since thelime added during juice purification is fully re-tained in the carbonation sludge (see page 26)and is largely present as calcium carbonate, ef-forts have been made to completely or partiallyreburn the carbonation sludge.
On addition of 1.5% of CaO (beet based),the following average composition of the car-bonation sludge (solids based) can be expected:48–50% CaO, 0.9–1.2% MgO, 0.3% K2O andNa2O, 1.7–2.1% PO3−
4 –SO2−4 , 23–26% CO2,
2–5% SiO2 (sand, clay), and 10–15% organicsubstances (protein, pectins, polysaccharides,citric, oxalic, and malic acids, etc.). Dependingon the conditions of recalcination (temperatureand residence time), decomposition of the clayor sandlike components to soluble calcium alu-minates and calcium silicates can occur. Thisgreatly reduces the quality of the reburnt lime[207]. After reburning once, 50–55% of thedry sludge weight is recovered, and after re-peated reburning, a strong enrichment of MgO,calcium aluminate, silicate, calcium phosphate,and calcium sulfate occurs so that part of thecarbonation sludge must be discarded. In the
United States, a rotary kiln and a circular mul-tiple hearth furnace have been used for manyyears for reburning carbonation sludge [208].Attempts have been made on a pilot scale to re-calcine previously granulated carbonation limecake [207] with a fluidized-bed system and witha high-velocity reaction chamber [209], whichcan process the carbonation lime in its primaryparticle-size distribution (d ′ < 10 µm).
Carbonation Lime Cake as Lime Fertil-izer. In the past, naturally dried carbonationsludge was spread manually on fields by farm-ers to improve the soil structure of acidic soil.Today, only carbonation lime cake that can bespread on the ground by machines is sold. Forisolation, see page 26. The composition is givenin Table 12 [210].
Table 12. Fertilizer analysis of carbonation lime cake with60–70% solids content* (in kg/1000 kg) [210]Nutrients Average VariationBasic components calculated asCaCO3
* Other constituents ca 1 kg sulfur, 1 kg sodium, and 0.9 kg boron.
18. Desugarization of Molasses
To reduce losses of sugar in molasses, chemicalprocesses are used that are based on the fact thatsucrose forms poorly soluble compounds (sac-charates) with alkaline-earth hydroxides undercertain conditions. The structure of these sac-charates is still not understood clearly. Of themethods used (Strontian process, baryte process,Steffen process) [211], only the Steffen processis still important. It is used on a large scale in theUnited States, the CIS, Turkey, and Iran.
Steffen Process. This process can be oper-ated batchwise or continuously [212], at ca.
Sugar 51
10 ◦C (cold) or 65–80 ◦C (hot). If operated care-fully, ca. 40 kg of white sugar can be producedfrom 80 kg of molasses solids.
The molasses is diluted (e.g., to a solidscontent of 10–15%) and cooled to 10–14 ◦C.At this temperature, very finely ground CaO(<100 µm) is added slowly, with continuousstirring, until 0.7–0.9% of free CaO is presentin the solution. The precipitated tricalcium sac-charate (C12H22O11 · 3 CaO) is filtered off withfilter presses or belt filters, washed with water,and suspended in water. The filtrate containingthe nonsugar substances in molasses (Steffenswaste) can be used for isolation of glutamicacid, betaine, raffinose, etc., or evaporated togive vinasse (see Section 22.3). During the beetprocessing season, the tricalciumsaccharate sus-pension is used instead of part of the lime milkas the precipitating agent for juice purification.Outside the working season, the tricalcium sac-charate suspension is heated and calcium hy-droxide is precipitated as calcium carbonate bythe introduction of CO2. The sugar solution thusobtained is subsequently evaporated and boiled.
Apart from the Steffen process, chromato-graphic processes are being used on a large scalefor the desugarization of molasses (see Section14.3).
Membrane and electrodialysis processes,also with ion-exchange membranes, have notgained acceptance because of the short servicelife of the membranes used [213].
Isolation of Glutamic Acid, Betaine, Raf-finose, and Other Substances. Of all the non-sugar substances present in sugar beet, the sub-stances mentioned above are isolated on an in-dustrial scale. Glutamic acid is isolated fromthe spent wash from molasses desugarizationprocesses, especially from Steffen waste (af-ter hydrolysis of l-pyrrolidonecarboxylic acid);from the regeneration wash from deionizationprocesses; or from the nonsugar fraction in thechromatographic separation of molasses (seeSection 14.3). Processes for isolating aminoacids are described in [214].
Like glutamic acid, betaine [215] can also beisolated from molasses on an industrial scale,today preferentially by chromatographic sep-aration [172]. Raffinose [216], inosite [216],galactinol, and kestoses can be isolated from
molasses by chromatographic separation aswell.
19. Sugar Yield, EnergyRequirements, Processing Aids,Water, and Working Time
The sugar yield is very important for the prof-itability of a sugar factory. In a modern mode ofoperation (continuous extraction process, goodjuice purification and crystallization) with exactoperation control, the sugar losses occurring ina white sugar factory are listed in Table 13.
Table 13. Sugar losses in a white sugar factory (kg sugar per100 kg beets)Type of loss Portion of
sugar lostSugar containedin side products
Respiration loss during storage(average of 8 d) between harvestingand processing
0.12–0.20
Losses during fluming and washing 0.10–0.25Extraction losses in pressed pulp 0.20–0.30Unaccounted losses* 0.15–0.40Losses in molasses 1.6–2.1Average total losses 0.6 2.1
* Sucrose losses due to bacterial activity, sucrose destructionduring juice purification, evaporation, and boiling.
If the beets have a sugar content of 16.0–17.5%, 13.3–14.6 kg of white sugar is obtainedper 100 kg of beets. Since the amount of ac-counted and unaccounted losses does not varygreatly, the sugar yield depends primarily on thesugar content of the beets.
The sugar yield can be increased by 0.3–1.5 kg per 100 kg of beets by the use of ion-exchange or molasses desugarization processes.
The primary energy required for the boilerhouse (i.e., only for sugar production) is 20–25kW · h per 100 kg of beets and for cossette dry-ing, 2–3 kW · h per 100 kg of beets. Since the1970s, the total primary energy consumption inthe European sugar industry has decreased bymore than 50%.
Limestone consumption is about 2–5% (beetbased), and the coke requirement for burninglimestone is 7–10 kg per 100 kg of limestone.
Other processing aids employed includeacids (sulfuric, hydrochloric, SO2), hardeningagents (calcium sulfate, calcium chloride), dis-infectants (formalin, hydrogen peroxide), an-tifoaming agents, antiscaling agents, activatedcarbon, and filter aids.
52 Sugar
Theoretically, a sugar factory requires no ad-ditionalwater supply fromgroundor surfacewa-ter because with the sugar beets, 0.75 m3 of wa-ter is fed per tonne of beets into the productionprocess as condensate and ca. 0.35–0.45 m3 ofwater is required per tonne of beets for supple-menting thewater cycles (0.25–0.3 m3 per tonneof beets for the flume water cycle, 0.1–0.15 m3
per tonne of beets for evaporation water lossesin the cooling water cycle).Wastewater from theflume water cycle and surplus condensate aretreated biologically before they enter the waste-water receiving stream.
In practice, however, at the start of the work-ing season the water cycles must be filled withground or surface water.
To process 1 t of beets, including delivery andunloading of beets and storage of the sugar in si-los, 10 working minutes are required during theworking season, depending on the size, mecha-nization, and automation of the factory. On theother hand, the total work requirement per yearamounts to 30–40 working minutes, includingthe time required for packing and dispatching,plant maintenance and repair, and general ad-ministration.
20. Cane Sugar
Production and consumption figures for canesugar are provided in Tables 1 (Section 2.1) and18 (Chap. 23).
20.1. Sugarcane Cultivation
Sugarcane is a giant tropical grass; Saccharumofficinarum, the cane of commerce, is a complexhybrid of several Saccharum species. Constantdevelopment of new varieties through cross-breeding and selection is essential to maintaindisease resistance and healthy crops with highsucrose content. Seed crossings (bi- or poly-)produce multiple interspecies varieties; selec-tion takes place over eight to twelve years. So-moclonal variation in sugarcane has preventedreplication by tissue culture; the varieties se-lected are increased by vegetative reproduction.The same procedure is employed in cane plant-ing: a section of stalk with one or more buds(each node has at least one bud) is planted; roots
develop; then a shoot appears. Cane is planted,manually or mechanically, in single or multiplerows, in furrows, and covered with soil. Plant-ing season and fertilizer, pesticide, and growthregulator applications vary tremendously fromthe subtropical areas (Louisiana, Pakistan, Mo-rocco) to the optimum growing tropical areas(North Queensland, Colombia, Cuba). Gener-ally, replanting is not necessary after each har-vest: buds on the plant base and roots remainingwill sprout again to produce another crop, calledratoon or stubble; this ratooning is repeated un-til the yearly decline in yield (successive ratoonsyield lower cane tonnage) is no longer econom-ical. Ratoon crops vary from none in Hawaii,where push-rake harvesters can harvest rootswith the stalks, to eight to ten in optimum re-gions: two to four ratoon crops are customary.
Cane pests include insects (borers, leaf hop-pers, grubs, aphids) and vertebrates (rats, pigs,and elephants), which eat and trample cane.Other diseases, now often controlled by breed-ing, includemosaic, rust, smut, and ratoon stunt-ing disease. The most common weeds are othergrasses and therefore difficult to control withherbicides.
Sugarcane is the most efficient collector ofsolar energy in the plant kingdom, convert-ing 2% of available solar energy into chemi-cal bonds of stored compounds, chief amongthem sucrose. Yield in tonnes of cane per hectarevaries from 55–60 t in poor growing areas tomore than 200 t for cane grown for 18–24months in optimum areas (e.g., Hawaii). Thequantity of sugar produced per hectare variesfrom ca. 5.0 t (Ethiopia) to ca. 26 t (Campos,Brazil).
Harvest season is generally during the cooler,drier part of the year, varying from three months(October–December) in Louisiana, to the firsthalf of the year in most Northern Hemispheretropics and the second half in most SouthernHemisphere tropics, to year-round in Hawaii,Colombia, and Peru.
20.2. Composition of Sugarcane
Sugarcane stalks, the portion of the plant desir-able for milling, contain 73–76 wt% water and24–27 wt% solids (10–16 wt% soluble solids,11–16 wt% dry fiber); the inclusion of “trash”
Sugar 53
(trash is defined as leaves, tops, roots, weeds,soil, and other extraneous matter) will increasethe total solids level but decrease the sugar con-tent of the mass, and thereby of the cane juice.The sugar (sucrose) content per tonne of canevaries from 75 kg in marginal growing areas orwith overratooned or diseased cane, tomore than140 kg in very good quality cane.
The soluble solids content (in percent) in thejuice is listed as follows [7]:
Other organic nonsugarsProtein 0.5–0.6Starch 0.001–0.050Gums 0.30–0.60Waxes, fats, phosphatides 0.05–0.15
Other 3.0–5.0
The major amino acids are aspartic and glu-tamic acids; the major inorganic salts are chlo-rides and sulfates of potassium, calcium, andmagnesium. The level of invert sugar decreasesas sugarcane matures, but increases at the ex-pense of sucrose concentration after cane is cut(or wounded), with a concomitant decrease inpH.
Concentration of nonsugars relative to su-crose, or juice purity (see Section 5), affects thepotential isolation of sucrose: in general, highernonsugar levels or lower purity make sucroserecovery difficult and decrease yield.
Sugarcane fibermakes up 10–17 wt%ofmil-lable sugarcane. Called bagasse after the millingstage, cane fiber has three components: (1) in-ner stalk pith (containing most of the juice); (2)fiber in the outer stalk and small fiber bundles inpith; and (3) nonfibrous, wax-coated epidermis,in the ratio 6 : 13 : 1. Bagasse is composed ofcellulose (40–60%), hemicelluloses, especiallyl-xylan (20–30%), and lignin (15–21%) [14].
20.3. Deterioration of Sugarcane
The composition of sugarcane after it is cut (har-vested) orwounded by freeze or pest damage can
change drastically and rapidly. “Stale cane is ananathema to the whole industry: growers losetonnage and processors lose sugar” [217]. Dete-rioration is both chemical and microbial: chem-ical deterioration includes hydrolysis of sucroseby invertases; the invert sugar formed contin-ues to decompose partly during juice purifica-tion to colorants and acids, which lower thepH of the juice and increase inversion. Degra-dation (and sugar loss) by microorganisms in-vading open cane tissue includes yeast infection(causing production of ethanol, lactic, and aceticacids) and bacterial infection, especially fromLeuconostoc mesenteroides, which converts su-crose to dextrans (long-chain polymers of glu-cose) and organic acids [218, 219]. If present injuice at concentrations >1000 mg/kg, dextranscan increase viscosity of juices and syrups; hin-der clarification, filtration, crystallization, andcentrifugation; and lower sugar yield [7, 14,220]. The deterioration rate increases with tem-perature, mud on cane, and time. Deterioration,which varies in rate with variety, can best becontrolled by minimizing cut-to-crush time (seeSection 20.4) and processing frozen cane asrapidly as possible. Bactericide application isnot practical in fields or cane yards; treatment inthe factory, to control further dextran formation,with the few approved biocides has proved tooexpensive and impractical [220]. Clearing withsteam or very hot water spraying of equipmentis the recommended factory treatment.
20.4. Harvesting and Delivery
Harvesting. More than 60% of the world’ssugarcane is harvested by hand in the trop-ics, where labor is available and employmentis desirable. Cane knives range from long ma-chetes to shorter-handled Australian and Brazil-ian knives with hand guards. Cane leaves andtops –which contain little sugar, add weight totransport, hinder cane cutters, and wear downmill rolls – are removed first by burning the canefield and then by hand or mechanical harvesters.Cane stalks are sufficiently high in moisture sothat controlled and rapid burns (fire in a 50-ha field will be complete in 3 min) incinerateonly the leaves, tops, and trash. In Australia andHawaii, cane is harvested without burning, to
54 Sugar
Figure 13. Constant-ratio cane mill with pressure feeder combination
provide more fiber as fuel (for electricity co-generation at the factory) and for environmentalprotection [221]. Important factors in cutting areto produce clean, undamaged cane, free of trash,and to leave viable root stock in the field. Me-chanical harvesting is found in Australia, theUnited States, some Caribbean and Latin Amer-ican Countries, and new developing cane areasin Southeast Asia. Most common are combineharvesters, or chopper harvesters, developed inAustralia, which cut cane stalks at the base, cutthe stalk into billets [9 to 15 inches (i.e., 28–38cm) long], blow excess leaves and trash off thebillets, and drop the billets into a cane cart pulledalongside the combine harvester. In Louisiana,or where tonnage is light, soldier harvesters cutand top erect cane, leaving rows of whole stalksin the field, which are burnt after harvest be-cause the canopy is too light to support a burn onstanding cane. Other whole-stalk harvesters inHawaii, where cane tonnage is heaviest, are theV-cutter, which cuts cane at base but not at top,
and the push-rake, which pushes cane, includ-ing the roots, out of the ground (used on hilly ar-eas), necessitating replanting. Under good con-ditions, a man can cut 0.5 t of cane per hour, anda combine harvester 30 t of cane per hour, withother mechanical systems between 15 and 30t/h. Mechanical cutting is always more expen-sive than hand cutting and yields lower quality,more damaged cane and an increased portion oftrash, but is increasing for sociological reasons.
Transportation. Cane loading in the field isaccomplished by hand, grab loaders, or contin-uous belt loaders, into small bins or wagons,which collect at transloader stations for trans-fer to larger transport containers. In some areas(India, Pakistan, Southeast Asia, Africa), caneis still transported in small bullock carts. Trans-port by narrow gauge railroad (cheapest) contin-ues in Australia and the Philippines; by water,in China, Southeast Asia, and Guyana; and byroad, elsewhere. Chopper-harvested cane must
Sugar 55
be shipped directly to the mill and be processedon arrival, not stored in the mill yard, to preventserious deterioration: delivery time of less than24 h is recommended [220].
Harvesting and shipping schedules are de-cided between grower and processor to ensurea constant supply of cane for the mill, and a fairdistribution of maturity and quality.
Cane payment is generally based on weight,with a deduction for trash. Where paymentfor cane quality (weight, sucrose content,fiber, sugar yield) has been introduced (UnitedStates, South Africa, Australia, Brazil, Colom-bia, Philippines), the quality and efficiency ofthe industry have greatly improved [222].
20.5. Sugarcane Processing: Milling andDiffusion
Cane that arrives at the factory (or mill, Cen-tral, Ingenio, or sugarhouse) is either processeddirectly or stored temporarily (preferably <12h) in the factory yard. Because factories oper-ate 24 h but transport is only by day, cane isstored in delivery vehicles or piles in the fac-tory yard for nighttime grinding. Hygiene andprompt use are important for good sugar yields.The cane is then loaded onto a moving table toenter the factory. Sugarcane factories generallyrun during the entire harvest season, shuttingdown temporarily only to clean out evaporators(see Section 20.5). Hawaiian andAustralian fac-tories close on weekends. Factories range in sizefrom 300–400 t of cane per day (tcd) in someless developed areas, through the usual rangeof 4000–10 000 tcd, to the large Florida facto-ries of 20 000–25 000 tcd, and the giant Brazil-ian processors of>40 000 tcd, where ethanol isproduced in addition to sugar.
Cane Weighing and Testing. Cane isweighed in the delivery vehicle (other thanboats) on platform scales, with a second weigh-ing of the empty vehicle. When payment isbased on cane quality, samples are taken fromthe truck (grab sample or, better, core sampler)[222] for analysis or from a hatch opening acrossthe mill after the knives; the most modern sys-tem (Florida) is to sample the first mill juicefrom cane, on an accurately timed basis, wherethe truck is labeled and the label is related by
a timing system to the juice from that truck’scane.
20.5.1. Cleaning
Hawaiian factories, where cane arrives withroots, mud, and rocks, first dry-clean cane toremove loose debris; then the cane is washedextensively. Louisiana factories, and others inmuddy areas, wash cane on the ascending caneconveyer or feeder table as it enters the mill.Magnets above the table remove metal trash.Sand must be removed especially carefully be-cause it can lead to erosionof downstreamequip-ment.
20.5.2. Juice Extraction
Cane is prepared for extraction through chop-ping with sets (usually two) of revolving knives,which slice it into small pieces (1–4 inch, ca.2–10 cm, ideally) but do not extract juice. Canepasses from knives through a shredder, often aswing-hammer mill, which mashes up the slicedcane, breaking open cells to allow increased ex-traction at the next stage. Juice is then extractedby either milling or diffusion.
Milling. Shredded cane passes through acrusher mill and a series of three to seven sub-sequent sets of three-roll mills. The rolls are 2–3 m long. These mills are built in a multitudeof structural variations. Four- or five-roll millsare becoming more common. A three-roll millwith pressure feeder combination is shown inFigure 13. Continuous-pressure feed improvesthe speed and efficiency of extractions. Water(10–35% by weight of cane) is applied to themilling train in a reverse direction to the cane,on the last mill, with juice recycled backward,to increase extraction in a process called “imbi-bition.” Crusher juice is obtained from the firstmill; it is highest in sugar (12–17%). Last millor residual juice is that from the final mill (1–3% sugar). Juices from all mills are strained orscreened into tanks and called mixed or dilutejuice.
56 Sugar
Diffusion (see Section 7.4). The sugarcanediffusion process has been developed from sugarbeet extraction. Here, cane from the shreddermust be prepared further in a fiberizer, or ex-tended shredder, for best extraction. Because ofthis finer preparation, diffusion gives a higherdegree of extraction (93–98%) thanmilling (85–95%); therefore, further cane preparation is in-creasingly used in mill trains also. Finely pre-pared cane enters a multicell, countercurrentdiffuser of linear (→ Liquid–Solid Extraction,Chap. 2.3.2), diagonal (→ Liquid–Solid Extrac-tion), or circular design (→ Liquid–Solid Ex-traction, Chap. 3.1) [7, 15]. In the diffusers,shredded cane moves countercurrent to hot wa-ter (75 ◦C). This system is applied for cane diffu-sion. Various combinations of sets of mills witha diffuser are called bagasse diffusers. Bagasseemerging from the diffusermust be dewatered toreach the approximately 50% moisture of mill-run bagasse; at this moisture, bagasse can be fedas fuel to factory boilers.
20.5.3. Factory Fuel
Cane factories, except for those in the People’sRepublic of China and Cuba (where wood fiberis in short supply and bagasse is a fiber source),burn their own bagasse and are more than self-sufficient in energy, with excess energy usedfor cogeneration [Cuba, United States (Hawaii,Florida),Mauritius], distillery operation (Brazil,other South and Central American countries,Southeast Asia), or increasingly, a refinery at theend of the mill (a white end refinery).
20.6. Cane Factory Process
The factory process, outlined in Figure 14, isgeneral for the production of raw sugar, a light-brown product that will subsequently be refinedinto white and brown sugar food products (seeSection 13.1). Cane sugar has traditionally beenprocessed in two stages because sugarcane can-not be stored after harvest: a crude raw sugarproduct was made, seasonally, in cane-growingareas and shipped to areas of major consump-tion (North America, Japan, Northern Europe),where it was refined into final products. Raw
sugar is traded on the commodity futures mar-kets. A white sugar product (mill white, plan-tation white crystal) has traditionally been pro-duced at sugar factories in the tropics for localhousehold and industrial use; it is described inSection 20.7, and traditional refineries are de-scribed in Section 20.8.
Figure 14. Schematic of sugarcane factory process for rawsugar manufacturea) Mill or diffuser; b) Clarification; c) Multistage evapora-tion; d) Vacuum crystallization
Juice treatment for raw sugarmanufacture in-cludes clarification, evaporation, and crystalliza-tion. The mixed juice extracted from cane is atpH 4–5, dark colored, and turbid. For clarifica-tion, the juice is heated to < 75 ◦C to destroyinvertase and other enzymes, and treated withlime (milk of lime or lime in a sugar solution,named “lime saccharate”) at concentrations ofca. 0.5 kg of CaO per tonne of cane to increasethe pH and stop sucrose inversion. Many differ-entmodifications of the process exist, alongwithvarious designs of clarifiers and feeders; heatingand liming are sometimes done in reverse order,depending on juice purity. Lime and flocculatingpolymer (→ Flocculants, Chap. 2.2,→ Floccu-lants, Chap. 2.3, → Flocculants) settle out ofheated juice in the clarifier tanks, taking sus-pended and colloidal solids (bagasse, soil, in-organic material, waxes, gums) with them in aprocess called defecation. Clear, clarified juiceis pumped off the top of the clarifier tanks; mudsare pumped from the bottom and filtered on ro-tary vacuum dry filters, on which residual sugaris washed out. The filtrate is returned to themixed juice ormixedwith clarified juice; the lat-ter procedure is a source of contamination unlessfiltrate has been clarified with a flotation clarifi-cation step, e.g., talo filtration (see Section 20.8)[223, 224].
Clarified juice, which contains about 13–15% solids, is pumped directly to a series of
Sugar 57
multiple-effect evaporators, in which the vaporfrom the first effect is used to heat the second,and each subsequent effect (usually three to five)is operated at vacuum and lower temperature(see Section 9). Many designs and combinationsof evaporators are in use [7, 15]. Scale buildupin evaporator bodies reduces heat transfer andmust therefore be removed; for this “boilout,”the factory stops processing several times perseason, unless it has a second set of evaporators.Evaporator syrup (corresponding to thick juicein sugar beet processing) of 62–69% solids con-tent is the product. Syrup in some modern facto-ries is clarified in an additional step by flotationclarification to produce high-grade raw sugar forsale or for the factory’s own refinery [225].
Syrup is pumped to the crystallization sta-tion, a series of single-effect vacuum pans;again, many designs and combinations exist [7,15] (see also Section 10.1). In a pan, syrup isevaporated to supersaturation and seeded withfine sugar crystals, which act as nuclei for crys-tal growth. When crystals have grown to de-sired size and number, the crystal–syrup mix-ture (massecuite, fillmass) is discharged (the ac-tion of emptying the pan is called a “strike”)into a mixer, and from there to a centrifugal(basket-type, batch centrifugal for high-gradesugars, continuous for low-grade sugars), wherethe mother liquor syrup is spun off (“purging”)and the crystals are “washed” (i.e., sprayed witha fine stream of water in the centrifugal to re-move most of their syrup coating so that theymay be free flowing in bulk storage) (see Sec-tion 11).
Runoff syrup from the crystallized evapora-tor syrup (A-strike) is called A-molasses; it isboiled again to crystallization in a vacuum pan(B-strike, with runoff B-molasses). This serialboiling is continued usually three times (see Sec-tion 13.1), with various modifications, cuts, andcross-blending, to obtain the maximum yield ofsugar. Crystallization is the cheapest and mosteffective purification step; sugar syrups of pu-rity lower than massecuite are cooled in openstirred crystallizers at atmospheric pressure un-til sufficient crystals have formed for centrifugalseparation. Designs for crystallizers are as nu-merous as those for vacuum pans [7, 15]. Thelowest grade of molasses from which no moresugar crystals can be recovered economically isblackstrapmolasses, a heavy, viscous, bitterma-
terial containing 26–40% sucrose, 9–23% in-vert sugars, and at least 80% total solids. About24–40 kg of molasses is produced per tonne ofcane, depending on the purity of the cane juiceand the processing systems.
Sugar cane juices have a roughly ten timeshigher invert sugar content than beet juices buttheir amino acid content is 50% lower than thatof beet juices. Thus, color formation can be lim-ited by working at low temperatures and low pHvalues during juice purification. The invert sugaris not destroyed during all processing steps.
The A- and B-strike sugars are usually mixedto become the raw sugar of commerce, traded ona 96◦Z (pol) basis. Very high pol (VHP) sugarsof more than 98◦Z (pol), are produced in someareas (e.g., Hawaii and South Africa) [226] byremelting B-sugars and washing the A-productextensively, sometimes after syrup clarification.
Raw sugar is cooled and dried on belts con-veying it to bulk storage (dryers are not common)and is weighed into the warehouse. The customof bagging raw sugar for storage and shippinghas almost ceased.
20.7. Direct White Sugar Factory (seeSection 13.2)
The characteristic reagent in the processes fordirect white (mill white, plantation white) sugarproduction is sulfur dioxide (produced by burn-ing sulfur in air or from liquid SO2), which isused to inhibit nonenzymatic browning by ad-dition either directly into the juice or into thecarbonated syrup to lower the pH during sulfita-tion. Direct white sugar is produced by a varietyof processes:
1) Settling clarification and juice sulfitation [12,15]
2) Single or double carbonation with syrup sul-fitation [12, 15]
3) Blanco Directo process ( juice sulfitation;juice filtrate and syrup clarification) [223,224]
In all these processes, powdered carbon, inpressure filters, may be used for additional de-colorization. Various modifications of processes1 and 2, using carbonation methods similar tothose for beet sugar production, are usually ap-plied in India,China,Africa, SoutheastAsia, and
RGC
Resaltado
58 Sugar
Figure 15. Schematic of process for manufacture of Blanco Directo (direct white sugar)a) Mill; b) Clarification; c) Rotary vacuum filter; d) Filtrate clarification; e) Evaporation; f ) Crystallization
Figure 16. Schematic of raw sugar refining processa) Mingler and affination; b) Melter; c) Clarification ( phosphatation, carbonatation); d) Decolorization (granular carbon, bonecharcoal, ion-exchange resin); e) Vacuum crystallization
South America for sugar for domestic produc-tion and are discussed thoroughly in older liter-ature [12]. The above processes are supplantedin newer factories in these countries by type 3Blanco Directo processes (see Fig. 15), whichcan readily convert a raw sugar factory to pro-duction of white sugar of quality higher than thestandard mill white and suitable for food andbeverage processors in the tropics. Many facto-ries produce either direct white or raw sugar atdifferent time periods [227].
20.8. Refining [228] (see also Section 13.4)
Traditional cane sugar refineries use raw canesugar at 96 to 98◦Z (pol) as input (“melt”) andproduce not only a range of granulated and liq-uid sucrose products, similar to those describedin Chapters 14 and 15, but also a range of brownsugars and syrups, as well as edible syrups (mo-lasses). The brown products have characteris-tic palatable cane and cane molasses flavors,not available from sugar beet. A generalized re-fining scheme is shown in Figure 16. Refiner-ies are large processing plants operating aroundthe clock typically for five (weekend shutdown)or ten days (four-day shutdown). Fuel for free-standing refineries is fuel oil, natural gas, or coal,
according to local availability; a few refinerieshave extended their power plants to generate ex-tra electricity for the local grid; refineries at-tached to raw sugar factories use the factory’sexcess bagasse fuel.
The quality of incoming raw sugar isparamount for efficient operation. Sucrose con-tent (pol) is a universal quality criterion. Color,ash (inorganic), invert sugar, moisture, dextrancontent, and grain size are other criteria thatmay be included in raw sugar purchase contracts[229].
Raw sugar is weighed into the refinery fromrail car, ship, or raw sugar warehouse, and con-veyed to the affination station, where it is min-gled with a heavy syrup (80% solids content),then spun in basket centrifugals andwashedwitha spray of water to remove the added and the in-tegral syrup coatings. The washed raw sugar isdissolved (melted) to give a washed sugar liquorof ca. 70% solids content, which is pumped toclarification. Three types of clarification exist:
Phosphatation. Phosphate (phosphoricacid, P2O5, concentration up to 400 mg/kgsolids) and calcium hydroxide (as milk of limeor sugar solution of lime, up to pH 7.5–8.3)
Sugar 59
are combined with the sugar liquor in an aer-ated flotation clarifier (Williamson, Jacobs, orSucrest designs). Calcium phosphate forms, oc-cluding suspended solids and inorganics in itsmass, and floats to the surfacewhere it is scrapedoff by rotating blades. Clarified liquor (syrupsare called liquors in refineries) is pumped outfrom the bottom of the clarifier [7, 14, 15, 223].The process removes 25–40% color, ash, andturbidity from the sugar liquor.
Talo Phosphatation. Phosphatation is per-formed as described above with the addition ofcolor-precipitating chemicals (quaternary am-monium compounds with long-chain fatty acidsubstituents) and a series of mud-desweeteningsteps, which remove a greater amount of color(30–50%), ash, and turbidity [223 – 225, 227].This process is widely used in white end re-fineries andhas almost replaced traditional phos-phatation.
Carbonation (Carbonatation in the UnitedStates and the United Kingdom). In this process,lime and carbon dioxide are mixed in liquor in atwo-stage process similar to that for beet sugarprocessing but carried out on liquor of 65–70%solids.
Any type of clarification is followed by fil-tration through leaf-type vertical or horizon-tal pressure filters. Carbonated liquors, con-taining calcium carbonate, may require additionof diatomaceous earth as a filter precoat. Phos-phatated liquors are generally filtered with theaddition of diatomaceous earth as precoat andbody feed.
Filtration, often a refinery bottleneck, espe-cially with poor-quality raw sugar, is followedby decolorization with bone char (traditional),granular activated carbon (now most common),or ion-exchange resins, or any combination ofthese (see Sections 13.4, 14.4). Discussions oncomparativemerits and regeneration of these de-colorizing systems may be found in [7, 15, 230,231].
Decolorized liquor, or fine liquor of very paleyellow color, is evaporated further to 72–74%solids and sent to crystallization in a series ofvacuum pans, as with raw cane sugar and beetsugar. Refinery strikes are designated 1, 2, 3, etc.Four to six white sugar strikes are common. Thelowest-grade runoff syrups are sent to a second
series of pans and crystallized to improve sugarrecovery.Brown low-grade runoff syrups and re-finers’ final molasses are sold for food process-ing, brewing, and blending to make cane syrupsand edible molasses.
Refined brown sugars (“soft sugars” in thetrade, seeSection 15.7) aremadeby crystallizingsugar from a mixture of third and fourth runoffsyrups and affination syrup (boiled brown sug-ars) or by coating white sugar crystals with abrown-liquor–caramel-syrup (painted or coatedbrown sugar). Table 14 shows the composition oftypical raw cane sugar and of refined granulated,direct mill white, and Blanco Directo sugar.
White end refineries are referred to above.These have the advantage of using availablefuel from the raw sugar factory to which theyare attached, although this may require seasonaloperation. Increasingly, raw sugar factories aregrouping together and building a white end re-finery to process their raw product [224]. Pro-cesses employed are typically melting withoutaffination because the raw sugar can be washedwell in the factory; use of color precipitants(talo phosphatation); decolorization with granu-lar activated carbon or ion-exchange resin; andcrystallization. Customarily, only white sugar ismade, and low-grade syrups are returned to theattached raw sugar factory. This system seemsto be the trend for the future, replacing the largefree-standing refinery.
21. Sugar from Other Plants
Palm Sugar. The production of palm sugaris of some importance in India (production170 000 t/a), Burma (production 20 000 t/a), In-donesia, and in the Philippines. Of the ninespecies of palmwith sucrose-containing cell sap,four are cultivated in India: Phoenix sylvestris,Borassus flabilliformis (palmyra), Cocos nu-cifera (coconut), and Caryota urens (sago). Thetapping of palm juice (neera) is accompanied bymany difficulties.
After purification with lime and skimming ofthe floating precipitate, the palm juice is concen-trated to a thick syrup by evaporation in openpans [232]. It is vigorously stirred as the su-crose begins to crystallize. This “massecuite” isthen filled into clay molds or palm-leaf baskets
60 Sugar
Table 14. Composition of typical raw, refined granulated, direct mill white, and Blanco Directo sugars [212, 219]
through which the mother syrup can drain off.For the production of 1 t of palm sugar, ca. 2.3 tof palm syrup with a solids content of 60% anda purity of 84% are required [24].
Maple Sugar and Maple Syrup [23]. Inthe United States (especially the state of Ver-mont) andCanada,maple syrup andmaple sugarare isolated from the juice of the sugar maple(Acer saccharinum). Maple syrup and maplesugar are used in the production of food syrup,preserved food, jams, and ice cream and in thefermentation of tobacco because of their specialflavor. Annual production in the United States isca. 9000–10 000 t of maple syrup and 130–150 tof maple sugar. Juice is tapped frommaple treesfrom February to April. The tree must be about40 years old before juice can be obtained. It thenproduces juice containing 2.5–3.5% sucrose for100 years. The juice is tapped from a hole boredin the trunk about 1 m from the ground. Beforeevaporation, maple juice is purified by addingmilk of lime, and the precipitate is filtered off.About 0.9–1 kg of maple syrup with a solidscontent of 66.8% (66.1% carbohydrates and0.7% ash) is obtained per tree per year [233].
Sugar from Sweet Sorghum. Like sugar-cane, sorghum (Andropogon sorghum saccha-ratum) [22] belongs to the class of grasses. Itis grown in the southern parts of the UnitedStates for production of a sweet syrup and wasstudied as a sugar and energy crop in, e.g.,Brazil, Hungary, Austria, Italy, Germany, Bel-gium, Greece, and Spain. As with sugarcane,the cell juice, which contains ca. 10–14% to-tal sugars (glucose, fructose, and sucrose), isobtained by pressing. Subsequent process stepsare also similar to those used in the cane sugarindustry. In Louisiana, extensive cultivation was
attempted to prolong the total working time ofa factory by introducing a sorghum campaign.
Date Sugar Syrup. Ripedates contain about30% water. The largest part of the solids is wa-ter soluble and consists mainly of glucose, fruc-tose, and small amounts of sucrose. The seed isa problem in processing dates to liquid sugar.Nevertheless, techniques [20] for the isolationof invert sugar from dates have been worked outand are used on a large scale in Iraq.
Sugar fromSweetCorn (Zea Mays L.). Theisolation of sugar from the sucrose- containingcell juice of corn stalks has achieved no technicalimportance [21].
22. Quality Demands on Sugar andSide Products of Sugar Production
22.1. Refined and White Sugar
In the past, white sugar was divided into “re-fined sugar” and “white sugar.” “Refined sugar”referred to a sugar obtained by recrystallizationof crystalline sugar.
Today, white sugar is evaluated and labeledonly according to its chemical and microbiolog-ical quality. Since white sugar is a commercialproduct worldwide, specifications for it exist inthe form of official, internationally and nation-ally obligatory regulations or standards in phar-macopeias, and voluntary quality agreementsbetween sugar manufacturers and the sugar pro-cessing branches of industry.
The sucrose content of white sugar is almostalways > 99.7%. For this reason, evaluation isbased not only on the content of water, invertsugar, SO2, heavy metals, etc., but also on the
RGC
Resaltado
Sugar 61
cumulative parameters for the individual classesof impurities, such as:
1) Ash content (i.e., content of inorganic or or-ganic salts)
2) Color in solution (i.e., content of Maillardproducts and colored higher molecular masscompounds)
3) Color type (i.e., optical appearance of thesugar by visual comparison with a type se-ries)
The Codex Alimentarius [234] divides whitesugar into two categories, A and B, and stipu-lates certain requirements for them (Table 15).Specifications valid within the EC [187], whichhave been accepted bymany other countries, aregenerally used in international white sugar trad-ing (Table 16). The requirements to bemet in theUnited States are published in the Food Chemi-cal Codex [188].
Table 15. Essential composition and quality factors for whitesugar, according to WHO–FAO [234]Specification A BSucrose content, ◦Z >99.7 >99.5Invert sugar content, % <0.04 <0.1Conductivity ash, % <0.04 <0.1Loss on drying (3 h at 105 ◦C), % <0.1 <0.1Color, IU * <60 <150Food additives, mg/kgSulfur dioxide <20 <70
Identification: Dissolve 26 g of the sample inwater and dilute to 100 mL at 20 ◦C. Determinethe polarization in a saccharimeter, by using a20- cm tube.
Further quality requirements for white sugarare as follows:
Sucrose content, ◦Z 99.8–100.2Arsenic (as As), mg/kg < 1Color, ICUMSA units < 75Conductivity expressed asresidue on ignition, % < 0.15
The heavy-metal contamination of whitesugar is very low (Pb < 0.1 mg/kg; Cd < 0.002mg/kg; Hg < 0.003 mg/kg within the limits ofdetection). The same applies to the concentra-tion of herbicides, fungicides, and insecticides,which lie within the analytical limit of detection.
Apart from these official minimum require-ments, other parameters are important for stor-age and industrial processing [235]. These in-clude the total (< 0.06%) and surface water(< 0.03%) content [197]; the content of water-insoluble solids [236],whichmust be< 7 mg/kg(determined with an 8-µm filter) for some con-sumers; and the filth [237] (insect parts and ro-dent hairs). Furthermore, for the beverage indus-try, the saponin content (< 1 mg/kg) of whitebeet sugar and the polysaccharide content (dex-tran < 100 mg/kg) of white cane sugar are im-portant because both cause foam and floc forma-tion [238]. The content of betaine, amino acids,and cations (calcium) can also be of significancein individual cases [239].
For storage in small silos (up to 100 t), theemptying and internal factory transport of sugarto the places of use, dust content (< 200 µm),and grain-size distribution are of substantial im-portance. Sugar with a d ′ of 1.0–1.2 mm, n >3, and a dust content of< 1.5% is most suitablefor this purpose.
The screen analysis of sugar is evaluatedaccording to the RRSB (→ Size Enlargement,Chap. 3.3) or to the Gaussian distribution (→Size Enlargement, Chap. 3.3).
Although sugar is a food with one of the low-est germ contents, certain consumers (manufac-turers of nonalcoholic drinks, canned food in-dustry, etc.) demand practically germ-free sugar(total content ofmicroorganisms< 200per 10 g,yeast, mold < 10 colonies per 10 g etc.). Targetvalues for the permitted microorganism burdenof sugar, especially for “liquid sugar,” have beenput forward by the National Soft Drink Associ-ation, United States (Bottlers Test), and the Na-tional Canners Association, United States [240](Canner’s Test), and are maintained by the sugarindustry on a voluntary basis. The internation-ally recommended microbiological methods ofanalysis are found in ICUMSA proceedings orin the ICUMSA Methods Book [55].
62 Sugar
Table 16. Quality criteria for white sugar according to EC sugar market regulations (EC 1972) (grade 2 is white sugar of standard quality),according to [187]Quality criterion Grade*
Color of solution, IU (max.) (22.5) (45)Points (7.5 units = 1 point) 3 6
Points according to EC point system (max.) 8 22
* Quality criteria for all grades: sound, fair and marketable quality, dry, in homogeneous granulated crystals, free-flowing.
22.2. Molasses
If molasses is used in feed, it must complywith feed regulations of individual countrieswith respect to composition, heavy-metal con-tent [241], agricultural pesticide residues [242],and labeling as single or mixed feed. The sameapplies to other feed obtained in the productionof sugar, such as pressed pulp, dried pulp, mo-lassed dried pulp, residual molasses, etc.
If molasses is sold as a raw material (nutrientmedium) for the production of ethanol, yeast,citric acid, or lactic acid, and for other chemicalor biochemical processes, general trading condi-tions or as-agreed specifications are valid [solidscontent (min.) 76.3% = 40.5◦Be].
Beet Molasses. Beet molasses accumulatesin production with a solids content of 80–89%.Apart from sucrose, the solids in molasses com-prise, depending on purity, 40–50%of nonsugarsubstances, which can be divided as follows[243] (all nonsugars = 100%):
1) Other usable saccharides such as glucose,fructose, raffinose, kestoses, and galactinol(1.5–4%)
4) Nonsugar substances containing no nitrogen:citric, malic, fumaric, succinic, oxalacetic,
oxalic, tartaric, glycolic, lactic, arabonic, sac-charinic, formic, acetic, propionic, butyric,and glacturonic acids; araban and galactanfragmentsApart from these constituents, other com-
pounds have been detected in the part-per-million range in beet molasses [245]. Investi-gations have been carried out in past years be-cause molasses- containing substrates have oc-casionally suffered from inhibition of growth ormetabolism, which was assumed to be causedby pesticide residues. The investigations couldnot verify these assumptions [246]. However,increased concentrations of volatile carboxylicacids (formic and propionic acids) and furfural-like compounds, which can arise on heat treat-ment of molasses in the acidic range, appear toexert inhibitory effects under certain conditions.
Cane Molasses (Blackstrap). Cane mo-lasses has a different composition from beetmolasses because the components of sugarcanecell juice are different. According to [247], nor-mal cane molasses with a water content of 17–25% has a total sugar content (sucrose, glucose,fructose) of 45–50%. The content of polysac-charides (dextrans, pentosans, polyuronic acids)is 2–5%, and that of peptides and free aminoacids is 2.5–4.5%. The content of nitrogen-freeacids (aconitic, citric, malic, oxalic, mesaconic,succinic, fumaric, and tartaric acids) is 1.5–6%.The content of cations, determined as carbonateash, varies between 7 and 15%.
The carbonate ash has the following com-position: 30–50% K2O, 7–15% CaO, 2–14%MgO, 0.3–9% Na2O, 0.4–2.7% Fe2O3, 1–7%SiO2 and insoluble substances, 7–27% SO2−
4 ,12–20% Cl−, and 0.5–2.5% P2O5.
Sugar 63
The storage of cane molasses is problematicbecause of its low pH. Chemical or microbio-logical decomposition of cane molasses storedin tanks occurs from time to time [248].
Canemolasses can be utilized in part like beetmolasses (see above), e.g., as pelletizing aids. Itbehaves differently as a fermentation substrate;because of its aromatic taste and odor, it givesrise to arrack and rum on alcoholic fermenta-tion. Aconitic and itaconic acids are obtainedfrom cane molasses [249].
Three types of cane molasses are availablecommercially, corresponding to the water andsugar (sucrose, glucose, and fructose) content:superior blackstrap molasses (water content =23.4%, total sugar content = 53.5%), black-strap molasses (water content = 23.5–26.4%,total sugar content = 48.5–53.4%), and utilityblackstrap (water content = 26.5%, total sugarcontent = 42.5–48.4%).
High-Test Molasses. High-test molasses isnot molasses in the original sense of the word,which defines it as the final syrup obtained aftercrystallization of sugar. It is rather a thin juicethat is two-thirds inverted, only moderately pu-rified, and concentrated to about 85% solids.High-test molasses consists of about 15.5%wa-ter, 27.0% sucrose, 50.0% invert sugar, and2.25% ash.
Dry Molasses. As a result of its high viscos-ity, molasses is difficult to handle and, conse-quently, cannot be used alone as feed in agricul-ture. To open up this market, methods have beendeveloped for the production of both beet andcane dry molasses. The drying operation used iseither spray drying [250] or drum drying [251].To make drying possible, carriers (e.g., calciumoxide [250, 251]) or floury feeds [252] (e.g., al-falfa flour or whey powder) must be added to themolasses.
22.3. Vinasse
After the fermentable sugar inmolasses has beenbiotechnologically used and the compounds pro-duced have been isolated, the nonsugar sub-stances that are not assimilated and metabolicside products remain more or less completely
in the nutrient medium. In Baker’s yeast fer-mentation, for example, ca. 35–45% of the totalnitrogen content of the beet molasses is assim-ilated. These substrates are being increasinglysubjected to multiple-effect evaporation to givea solids content of 70%. They are referred to asvinasse or condensed molasses solubles [249].Vinasses have gained approval by feed regulat-ing authorities, and are used as feed or soil con-ditioner [253]. Efforts are also being made touse vinasse directly for the production of biogas[249].
22.4. Liquid Feed Supplement [254]
For large animal farms (cattle, sheep), a liquidfeed based on dilutedmolasses (60–70%) is pro-duced in the United States. Urea, biuret, min-eral substances, trace elements, vitamins, etc.,are added to optimize requirements in the basicfeed and are then added to this liquid feed.
22.5. Beet Pulp
Beet pulp obtained on extraction of cossettes ispressed to an appropriate solids content, depen-dent on individual factory conditions. If pressedpulp is delivered directly as feed or for preser-vation by ensiling, it is mostly pressed to 18–22% solids content. If pulp is dried after press-ing, factories try to achieve the highest possiblesolids content by pressing, mostly in the rangeof 28–35%, to save drying costs. Their solids,beet marc, consist of ca. 20–25% cellulose, 20–25% pectin, 18–23% araban, 5–10% galactan,6–10%rawprotein, 5–6%ash, and4–5%sugar.
In contrast to other agricultural animal feeds,pressed pulp is normally ensiled hot, at 50 ◦C,with the aid of thermophilic lactic acid bacte-ria [255]. Shrink-wrapped round bale ensiling,a well-known development in agricultural en-siling, was studied as a new way of marketingpressed pulp [256].
Dried pulp is obtained by drying pressedpulp (see Section 17.2) to a solids content of 90–92%. If 1–3% of molasses (based on the weightof the pressed pulp) is added to the pressed pulpbefore drying, molassed dried pulp with vary-ing sugar content (9–30%) is obtained. Apart
64 Sugar
from sugar content, the concentrations of HCl-insoluble substances, calcium, and ash are con-trolled in individual countries according to feedregulations.
Sepa patent cossettes are obtained by dryingon pressed pulp a previously homogenized mo-lasses preliming flocculation mixture(see Sec-tion 8.1). They have a solids content of 91–92%and consist of ca. 9.9% raw protein, 12.7% rawfiber, and9.8%rawashofwhich6.1% isCaCO3and 0.65% is P2O5. The sugar content is 17–18%. In the case of Torno slices, carbonationsludge (see page 26) is dried to 3% solids in-stead of the preliming precipitate.
“Steffen cossettes” are obtained by dryingpartially desugarized wet pulp (sugar content28–35%). Dried pulp with a total nitrogen con-tent of 2.5–3.5% is obtained directly by extrac-tion of cossettes with liquid ammonia (see Sec-tion 7.3) or by treatment of dried pulpwith liquidammonia in pressure vessels [257]. Feed witha high NPN (nonprotein nitrogen) total nitro-gen content can also be produced by additionof urea to a dried pulp–molasses mixture. Thefinished feed consists of ca. 60 parts of driedpulp, 25 parts of molasses, and 15 parts of urea.Another production process for amide cossettesstarts directly with pressed pulp [258]. To obtaina feed with a higher NPN-level also an aque-ous (NH4)2SO4 solution (1% based on dry sub-stance) can be mixed with pressed pulp.
Full-quality beet cossettes are obtained bydrying fresh beet slices (see Section 6.9) to asolids content of 92–94%. Their compositioncorresponds to that of fresh beet.
23. Economic Aspects
The worldwide sugar economy is determined bythe following factors:
1) Sugar is an agricultural product, affected bycrop failure and record crops (i.e., it is avail-able in changing supply)
2) The demand for sugar depends on eatinghabits, the economic situation, and populationdevelopment
3) Since the 1970s, apart from traditional glu-cose syrups, sugar has had a serious com-petitor in the form of HFCS (→ Glucose andGlucose-Containing Syrups)
Today, sugar is a staple food. In industrial-ized countries, 10–15% of the daily intake ofcalories is provided by sugar and sweetenersproduced from corn or wheat. In some coun-tries the sugar consumption per person per yearhas remained practically unchanged for decades.For instance, it remained virtually constant inthe United States and the United Kingdom from1920 into the 1980s.
Until 1850, the cane sugar industry alonedominated the market. About 5000 t/a was im-ported into Europe of which, on average, 10 kgper person per year was consumed in England, 7in the Netherlands, 2 in France and the German“Zollverein,” 1 in Austria and Italy, and 0.5 inRussia [259].
The beet sugar industry then developed inCentral Europe and became a competitor of thecane sugar industry. In an effort to be indepen-dent of imports, more andmore countries startedtheir own sugar production and switched frombeing importing to possible exporting countries.Nowadays, more than 100 countries have theirown sugar production from sugarcane or sugarbeet.
Countries that have a permanent sugar re-quirement do not buy sugar on the open market,but often conclude long-term supply contractswith exporting countries at preferential prices.For instance, the United States awarded exportquotas to individual countries, especially Cubauntil 1960. Thus, the United States was the mainpurchaser of Cuban sugar until that time. SinceFidel Castro’s revolution and until 1990, theEastern-bloc countries, the Soviet Union, andthe People’s Republic of China have receivedmost of the Cuban sugar. Sugar imports into theUnited Kingdom were also controlled by spe-cial regulations (Commonwealth Sugar Agree-ment of 1951) or arranged in agreements suchas the African, Malagasy, or the Lome Agree-ment (1971). In the latter, the countries of theEC were committed to buy 1.3×106 t of sugarper year from these countries at EC prices. Forthis reason, only a fraction, about 10–15%, ofworld sugar production is traded on the stockmarkets of New York, London, and Paris.
Since at all times and in all countries, sugarhas represented a source of taxes that are prof-itable and easy to raise, good statistics are avail-able. Table 17 shows the development of worldsugar production and cane sugar production as
Sugar 65
percentage of total production since 1900 [260].Worldwide sugar production has increased ten-fold since 1900. At more than 50%, the per-centage of beet sugar was at its maximum beforeWorldWar I. Since 1940, it has been in the rangeof 34% (1980–1992) to 40% (1960).
The reason for the favorable development ofbeet sugar production in 1964–1965 was wide-spread sugar beet cultivation in the Soviet Unionafter World War II. Since 1970, the percentageof cane sugar production has increased to about75% and has remained at that level.
Since July 1, 1968, ECmembers have formeda common sugar market based on decree No.1009/67 EEC from December 18, 1967, whichwas valid largely unchanged until July 2006. Forthe main areas of surplus production in the EC, atarget price and an intervention pricewere set forunpackedwhite sugar of a definite standard qual-ity ex factory (seeTable 16, grade no. 2). Raisinga surcharge for imports from third countries andpayment of a reimbursement on exports shouldcompensate for price differences within and out-side the EC. A desirable limitation of sugar pro-duction was achieved by establishing basic quo-tas with a price and sales guarantee by the ECfor each sugar-producing company (A quota: thelevel depends on domestic requirements in theEC). These guarantees were reduced (B quota)for the amount that exceeded the basic quantity(ca. 20–30% of the A quota). If the EC suf-fered financial losses due to exporting part ofthe quota, this was reapportioned among beetgrowers and sugar factories (production tax). Ifthe sugar production of a company exceeded theentire quota amount, this sugar (C sugar) had tobe sold within a year outside the EC and was thesole responsibility of the company.
Since the 1980s, development of the worldsugar market has led to tougher competitionamong previously nationally oriented sugar in-dustries. Antiquated factories have been shutdown or modernized with high investments. Asa result of transport costs, factories are now lo-cated in cultivation areas. For the same reasons,the size of factories is kept within limits.
In 2006, this tougher competition led to a re-form of the EU sugar regime, which was pub-lished as decree No. 318/2006 EC of Febru-ary 20, 2006 and which came into force onJuly 1, 2006, when the former EU directive ex-pired. This reformwas necessary especially after
a complaint by Australia, Brazil, and Thailandabout increased EU sugar exports with the aidof subsidies. This complaint was confirmed bya WTO panel in 2004 and again in 2005. Withthe new regime, the intervention system was re-placed by a white sugar reference price, whichis to fall by 36% until 2009 according to decreeNo. 318/2006 EC. A number of ACP (African,Carribean, Pacific) and LDC (least developedcountries) states as well as European countrieswill be unable to produce sugar at this low price.Thus, a restructuring fund was installed to en-courage uncompetitive sugar producers to leavethe industry, in order to reduce the pressure onthe EU domestic market. For sugar beet farm-ers a minimum price, to fall by 20% after threeyears, and a monetary compensation were fixed.A and B quotas were combined and new quo-tas were fixed, based on 2005/06 data [261].The new regime will ensure a sustainable futurefor the remaining EU sugar production, but willcause large changes for individual countries.
Regulations for the production of sugar(prices, quotas) similar to those of the EC alsoexist in other countries, such as the UnitedStates, India, and Brazil.
Consumption per person in a series of coun-tries is listed in Table 18 [262].
The world market price of sugar undergoeslarge fluctuations, as shown in Table 17 and Fig-ure 17.
Figure 17. World market and prices for white sugar,monthly values Paris 1988–1993 [263]
To stabilize production and prices, the sugarindustries ofCuba, Japan, Poland,Hungary,Bel-
66 Sugar
Table 17. Development of worldwide sugar production [260]
Raw sugar, 106 t Cane sugar, % Average annual quotation of the New Yorkstock exchange, cents/lb
gium, Germany, and Czechoslovakia signed anagreement on May 9, 1931, in Brussels (Chad-bourne agreement),which stipulated a limitationof sugar production in subsequent years. Thesupply (production and sales of surplus) shouldnot exceed the demand. The international sugaragreements of 1937, 1953, 1958, and 1968 hadthe same goal.
To increase the export proceeds of developingcountries and stabilize international trade, a newinternational sugar agreement came into effectin 1977, which was signed by 40 sugar export-ing countries and 15 sugar importing countriesand was the last one containing direct marketintervention instruments or so-called economicclauses [260]. This agreement was ratified bythe United States in 1980 and the EC partici-pated with constructive proposals, but was nevera member of the agreement. The aims of theagreement should be achieved by export quo-tas in combination with reserves, which shouldbe used in the case of increasing demand andrefilled in the case of falling prices. A mini-mum price for raw sugar of 13 cents per poundand a maximum price of 23 cents per poundwere agreed upon. The world market price wasin this desired range for only a relatively shorttime. An agreement on the financing of reservestorehouses could not be reached. Consequently,the intended stabilization of world market priceswas not achieved.
This agreement was replaced by a so calledadministrative agreement, ratified in 1984, 1987,and–after withdrawal of the United States–by aservice agreement, signed in 1993, 1995, 1997,1999, etc., with a possibility of indefinite exten-sions, each valid for two years. The aims noware merely to intensify international coopera-tion in sugar production and sales, to serve asa forum for international consultations on sugarand on the possibilities of promoting the worldsugar economy, to facilitate trade by recordingand making available information on the worldmarket for sugar and other sweeteners, and topromote the demand for sugar for new purposes.
In the past, beet and cane sugar and, to asmall extent, starch hydrolysates (glucose syrup,glucose) competed with each other on the mar-ket for nutritive sweeteners. Starch hydrolysatesare used for technological reasons in the indus-trial production of certain foods. Since 1975,HFCS (isoglucoses, → Glucose and Glucose-Containing Syrups) has appeared on the marketas a direct competitor of “liquid sugar” in theUnited States, Canada, Japan, and some Euro-pean countries. In 1991, the production ofHFCSamounted to 7.8×106 t (solids), ca. 7% of theworld sugar market. These amounts substan-tially influence the sugar market worldwide.
Apart from the market for nutritive sweet-eners, a market has developed for calorie-free(intense) sweeteners (→ Sweeteners), calorie-reduced (polyols, inulin hydrolysates, synthetic
Sugar 67
Table 18. Sugar consumption (in kilogram per person) in some industrialized and nonindustrialized countries, 1991 [262]
Area Consumption Area ConsumptionWorld 18.9 South America 38.1Europe 35.0 Africa 12.6North America 29.9 Asia 11.1
Industrialized countries Nonindustrialized countriesHungary 55.6 Cuba 82.0Iceland 49.5 Swaziland 63.1Israel 47.2 Columbia 61.9Czechoslovakia 47.2 Costa Rica 54.9Ireland 45.7 Fiji 54.2New Zealand 44.9 Gambia 52.3Australia 44.1 Mexico 47.7Switzerland 42.1 Panama 46.6Austria 41.2 Surinam 44.3Sweden 40.2 Brazil 43.7United Kingdom 38.2 Belize 42.6Norway 38.2 Persian Gulf 38.4Netherlands 37.9 Lebanon 38.2Canada 37.5 Guatemala 37.5Denmark 36.6 Libya 37.1France 35.7 Ecuador 35.7Germany 35.1 Malaysia 35.1South Africa 34.9 Jordan 33.7Portugal 31.7 Argentina 32.1Belgium–Luxembourg 29.3 Honduras 31.5United States 29.1 Algeria 31.3Italy 27.0 Syria 30.8Spain 26.5 Egypt 29.3Japan 21.2 Thailand 29.0
Pakistan 28.0Saudi Arabia 24.0Tunisia 23.0Iran 22.4Yemen 21.5South Korea 16.6Kuwait 16.5India 13.2Senegal 13.0People’s Republic of China 5.7Somalia 4.3Ethiopia 2.8Afghanistan 2.2Liberia 2.0Nepal 1.9Central African Republic 0.9Cambodia 0.5
polydextroses) sweeteners, and sweeteners witha definite nutritional physiological purpose [e.g.,suitable for diabetics, noncariogenic sweeten-ers (fructose,→ Fructose; polyols,→ Sugar Al-cohols)]. The percentages of individual productgroups fluctuate greatly from country to coun-try: for example, for intense sweeteners, ca. 10%of the entire sweetener market is in the UnitedStates, 5% in Germany, and < 0.5% in devel-oping countries [263].
24. References
General References1. P. W. van der Poel, H. Schiweck, T. K.
2. J. L. Multon (Coordin.): Le Sucre, Les Sucres,Les Edulcorants et les Glucides de Chargedans les I.A.A., TEC & DOC–Lavoisier, Paris1992.
68 Sugar
3. O. Bia: Tecnologia e Impianti IndustrialSaccariferi, Gruppo Ferruzzi Publishing,Eridania Beghin-Say 1992.
4. S. Marie, J. R. Piggott (eds.): Handbook ofSweeteners, Blackie and Son Ltd., GlasgowLondon 1991.
5. N. L. Pennington, C. W. Baker (eds.): Sugar, AUser’s Guide to Sucrose, Van NostrandReinhold, New York 1990.
6. G.-W. von Rymon Lipinski, H. Schiweck(eds.): Handbuch Sußungsmittel, Behr’sVerlag, Hamburg 1990.
7. J. C. P. Chen, Ch. Ch. Chou (eds.): Cane SugarHandbook, 12th ed., J. Wiley & Sons, NewYork 1993.
8. R. A. McGinnis: Beet-Sugar Technology, 3rded., “Beet Sugar Development Foundation,”Fort Collins, Colorado 1982.
9. Autorenkollektiv: Die Zuckerherstellung, 2nded., VEB Fachbuchverlag, Leipzig 1980.
10. K. Vukov: Physik und Chemie der Zuckerrubeals Grundlage der Verarbeitungsverfahren,Akademiai Kiado, Budapest, russ. ed. 1972;Physics and Chemistry of Sugar-Beet in SugarManufacture, engl. ed. 1977.
11. P. M. Silin: Technology of beet-sugarproduction and refining, Israel Programme forScientific Translations, Jerusalem 1964: russ.ed. PPI, Pishchepromizdat 1958.
12. P. Honig: Principles of Sugar Technology,Elsevier, Amsterdam vol. 1, 1953; vol. 2,1959; vol. 3, 1963.
13. H. M. Pancoast, W. R. Junk: Handbook ofSugars, 2nd ed., AVI, Westport, CT, 1980.
14. M. A. Clarke, M. A. Godshall (eds.):Chemistry and Processing of Sugarbeet andSugarcane, Elsevier, Amsterdam, 1988.
15. V. E. Baikow: Manufacture and Refining ofRaw Cane Sugar, Elsevier, Amsterdam 1981.
Specific References16. P. G. Morel du Boil, Int. Sugar J. 99 (1997)
102–106.17. J. Bricout, J. C. Fontes, Sugar J. 39 (1977)
31–32.B. N. Smith, Naturwissenschaften 62 (1975)390.A. Rossman, W. Rieth, H.-L. Schmidt, Z.Lebensm. Unters. Forsch. 191 (1990) 259–264.
18. W. R. Sponholz in G. Wurdig, R. Woller(eds.): Chemie des Weines, Verlag EugenUlmer, Stuttgart 1989, pp. 46–59.K. Mengel: Ernahrung u. Stoffwechsel derPflanze, Gustav Fischer Verlag, Jena 1991.
19. L. W. Doner in H. F. Linkens, J. F. Jackson(eds.): Analysis of Nonalcoholic Beverages,Springer Verlag, Berlin 1988, pp. 120–133.G. J. Martin, B. L. Zhang, M. L. Martin, M. L.Dupuy, Biochem. Biophys. Res. Commun. 111(1983) 890–896.
20. H. D. Wallenstein, B. Schubbar, Z. Zuckerind.14 (1964) 621–624, 674–676.K. Vukov, G. Patkai, J. Monszpart-Senyi, Z.Zuckerind. 27 (1977) 792–795.J. Ehrenberg, Zucker 30 (1977) 612–619.
21. J. Tschersich, Z. Zuckerind. 17 (1967) 638.22. J. H. Hulse, E. M. Laing, O. E. Pearson:
Sorghum and the Millets: Their Compositionand Nutritive Value, Academic Press, NewYork 1980.P. Angelle, Sugar J. 44 (1982) no. 10, 17–18.
23. C. O. Willits, C. H. Hills: “Maple SyrupProducers Manual,” Agriculture Handbook,no. 134, Agricultural Res. Service, USDA,Washington 1976.
24. G. W. Walawalkar, Sharkara 4 (1961) 20.N. Gopinathan, Int. Sugar J. 64 (1962) 9.T. Yamane in P. Honig (ed.): Principles ofSugar Technology, vol. 3, Elsevier, Amsterdam1963, pp. 507 ff.
25. Federal Register, 53, no. 215, Nov. 7.Washington 1988, 6.44862.E. H. Glinsmann, H. Irausquin, Y. K. Park(FDA), J. Nutr. Suppl. 116 (1986)Committee on Medical Aspects of FoodPolicy: Dietary Sugars and Human Disease,London 1989, pp. 1–44.K. H. Bassler: Z. Ernahrungswiss. Suppl. 29(1990).
26. E. Nagele, Zuckerindustrie 130 (2005)687–693.
27. E. O. von Lippmann: Geschichte des Zuckers,2nd. ed., Springer Verlag, Berlin 1929.J. Baxa: Die Zuckererzeugung 1600–1850,Fischer-Vlg., Jena 1937.J. Baxa, G. Bruhns: Zucker im Leben derVolker, Vlg. Dr. A. Bartens, Berlin 1967.S. W. Mintz: Sweetness and Power, The Placeof Sugar in the Modern History, PenguinBooks, New York 1986, German ed., CampusVerlag, Frankfurt 1987.
28. K. Maier, O. Baron, J. Bruhns:Zuckerwirtschaft Europa 2005 (Statistik Welt),Verlag Dr. A. Bartens, Berlin 2004, pp. 11–15.
29. E. O. von Lippmann in W. Ostwald (ed.):Klassiker der exakten Wissenschaft, no. 159, F.W. Engelmann, Leipzig 1907.
30. G. Vavrinecz: Atlas der Zuckerkristalle, VerlagDr. A. Bartens, Berlin 1965, p. 8.
Sugar 69
31. Z. Bubnik, P. Kadlec, D. Urban, M. Bruhns:Sugar Technologists Manual, Verlag Dr. A.Bartens, Berlin 1995, p. 116.
32. H. E. C. Powers, Sugar Technol. Rev. 1(1969/70) 86–190.G. Vavrinecz: Atlas der Zuckerkristalle, Vlg.Dr. A. Bartens, Berlin 1965.F. H. C. Kelly, Sugar Technol. Rev. 9 (1982)271–323.
33. R. W. Hartel, A. V. Selastry, Crit. Rev. FoodSci. Nutr. 1 (1991) 49–112.
34. G. Vavrinecz, Z. Zuckerind. 12 (1962)481–487.ICUMSA Methods Book, Verlag Dr. A.Bartens, Berlin 2005, sect. SPS-2 (1998), pp.1–3.
35. ICUMSA Methods Book, Verlag Dr. A.Bartens, Berlin 2005, sect. SPS-4 (1998), p. 13.
36. J. F. Swindells, C. F. Snyder, R. C. Hardy, P. E.Golden, Nat. Bur. Stand. Suppl. to Circ. No.C 440, July (1958),as quoted in R. S. Norrish, Sci. Tech. Surv. Br.Food Manuf. Ind. Res. Assoc. 51 (1967).
37. M. P. Maggean, J. U. Kristott, S. A. Jones:Physical Properties of Sugars and theirSolutions, Leatherhead Food R. A., Surrey, no.172, 1991.
38. A. C. Noble, N. L. Matysiak, S. Bonnans,Food Technol. 45 (1991) 121–126.
39. L. F. Wiggins, Carbohydr. Chem. 4 (1949) 293.R. Khan, Adv. Carbohydr. Chem. Biochem. 33(1976) 235–294.J. L. Hickson (ed.) Sucrose Chemistry, ACSSymp. Ser. 41 (1977).M. R. Jenner in Developments in FoodCarbohydrate, vol. 2, Applied Science Publ.,London 1980.C. E. James, L. Hough, R. Khan, Prog. Chem.Org. Nat. Prod. 55 (1989) 117–184.F. W. Lichtenthaler (ed.): Carbohydrates asOrganic Raw Materials, VCHVerlagsgesellschaft, Weinheim, Germany1991.F. Descotes (ed.): Carbohydrates as OrganicRaw Materials, VCH Verlagsgesellschaft,Weinheim, Germany 1993.F. W. Lichtenthaler, P. Pokinskyj, S. Immel,Zuckerindustrie 121 (1996) 174–190.
40. A. Durand et al.: “Abstracts,” VII InternationalBiotechnology Symposium, New Delhi 1984,pp. 464–467.Sudzucker AG, DE 3 812 612, 1988 (P.Nigam, M. Vogel).
41. M. Bruder: Solid-State Fermentation of SugarBeet Pulp; A New and Promising IndustrialProcess, British Sugar Techn. Conference,Eastbourne 1990. F. Lyvan, companybrochures, 14 630 Cagny/France.
42. A. Pictet, H. Vogel, Helv. Chim. Acta 11(1928) 436.
43. J. Levi, C. B. Purves, Adv. Carbohydr. Chem. 4(1949) 28, 31.
44. R. U. Lemieux, G. Huber, J. Am. Chem. Soc.75 (1953) 4118.R. K. Ness, H. G. Fletscher, Carbohydr. Res.17 (1971) 465–470.
45. M. Doudoroff, H. H. Barker, W. J. Hassid, J.Biol. Chem. 168 (1947) 725.G. Avigad: “Plant Carbohydrates I,” in F. A.Loewus, W. Tanner (eds.): Encyclopedia ofPlant Physiology, vol. 13 A, Springer Verlag,Berlin 1982, pp. 217–347.
46. W. Z. Hassid, M. Doudoroff, Adv. Carbohydr.Chem. 5 (1950) 29 ff.
47. W. Oltmann, M. Burba, G. Bolz, Beih. Z.Pflanzenzucht. 12 (1984) 36–41.N. J. Kruger in D. T. Dennis, D. H. Turpin(eds.): Plant Physiology, Biochemistry andMolecular Biology, Longman, New York1990, pp. 59 ff.
48. R. Giaquinta, Ann. Rev. Plant Physiol. 34(1977) 347–387.
49. R. A. Saftner, R. E. Wyse, Plant Physiol. 66(1980) 884–889.
50. C. E. Hartt, Rep. Hawaii. Sugar Technol. 22(1963) 151, 157.
51. F. Schneider: Sugar Analysis, ICUMSAMethods, ICUMSA, Peterborough 1979, pp.2–3.
52. ICUMSA Methods Book, Verlag Dr. A.Bartens, Berlin 2005, loose-leaf ed. 2005, sect.SPS-1, p. 3.
53. ICUMSA Methods Book, Verlag Dr. A.Bartens, Berlin 2005, loose-leaf ed. 2005, sect.SPS-3, pp. 1–8.
54. H.C.S. de Whalley, ICUMSA Methods ofSugar Analysis, Elsevier,Amsterdam-London-New York 1964.F. Schneider: Sugar Analysis,ICUMSA-Methods, ICUMSA, Peterborough,1979.
55. ICUMSA Methods Book, Verlag Dr. A.Bartens, Berlin 2005, last loose-leaf ed.
56. D. A. Cooke, R. K. Scott: The Sugar BeetCrop, Chapman & Hall, London 1993.B. Marlander: Zuckerruben, Bernhard-PatzoldDruckerei & Verlag, Stadthagen 1991.C. Winner: Zuckerrubenanbau, DLG-Verlag,Frankfurt/M. 1981.
70 Sugar
57. K. During, Nachr. Chem. Tech. Lab. 41 (1993)233.J. B. Nichols, C. C. Dalton, G. A. Todd, N. W.Broughton, Zuckerindustrie 117 (1992)797–800.
58. G. Buttner, M. E. Fuhrer Ithurrart, J.Buddemeyer, Zuckerindustrie 127 (2002)856–866.B. Marlander, I. Rothe, Zuckerindustrie 130(2005) 482–486.
59. M. Burba, E. Schulze, Zuckerindustrie 106(1981) 303.M. Burba, W. Haufe, Z. Zuckerind. 22 (1972)75.
60. G. Pollach, W. Hein, G. Rosner,Zuckerindustrie 121 (1996) 332–344.
61. B. Marlander, Zuckerindustrie 118 (1993) 131.62. M. Burba, Z. Zuckerind. 26 (1976) 647–658.
P. V. Schmidt: Zuckerruben-Lagerung,-Aufbereitung, Verlag Dr. A. Bartens, Berlin1990.
64. F. X. Kammerer, H. J. Delavier, Z. Zuckerind.17 (1967) 349, 419, 464.
65. Salzgitter Stahlbau AG, DE-OS 2 461 486,1974 (K. Kutzke, H. W. Rose).
66. G. Pollach, W. Hein, G. Rosner,Zuckerindustrie 124 (1999) 622–637.
67. L. Lambrechts, R. Wibon, A. Simonart, Sucr.Belge 87 (1967) 139.M. Devilliers, Sucr. Fr. 108 (1967) 289, 359.E. Reinefeld, Zucker 28 (1975) 397.
68. D. Sargent, S. Briggs, S. Spencer,Zuckerindustrie 122 (1997) 615–622.
69. P. Valentin, Zucker 27 (1974) 305–312.P. S. Worthington, Sucr. Belge Sugar Ind.Abstr. 101 (1982) 403–404.
70. L. Rigo, Zuckerindustrie 127 (2002) 31–44.71. H. Wunsch, Zuckerindustrie 130 (2005)
405–409.72. R. Hurasky, Zuckerindustrie 107 (1982)
926–930.73. C. Nahle, Zuckerindustrie 114 (1989)
703–705.J. P. Lescure, P. Bourlet, D. Verrier, G.Albagnac, Sugar Technol. Rev. 13 (1986)179–231.
74. H. Schiweck, C. Nahle, Zuckerindustrie 115(1990) 639–674.
75. H. Hartmann, H. van Malland, R. Hies, T. vonDoring, Zuckerindustrie 111 (1986) 634–642.
76. K. Vukov: Physics and Chemistry of SugarBeet in Sugar Manufacture, Akademiai Kiado,Budapest 1977.
L. Drath, R. Strauß, H. Schiweck,Zuckerindustrie 109 (1984) 993–1007.
77. G. V. Genie, Sugar Technol. Rev. 9 (1982)119–270.H. Bruniche-Olsen: Solid-Liquid Extraction,Nys. Nordisk Farlag, Copenhagen 1962.G. V. Genie, Int. Sug. J. 96 (1994) 124–128,160–162.
78. F. Schneider, H. P. Hoffmann-Walbeck: ZuckerBeihefte 2 (1953) 1.
79. K. J. Demeter, W. Kundrat, H. Neumann,Zucker 9 (1956) 5–8.H. Klaushofer, E. Parkkinen, Z. Zuckerind. 15(1965) 445–448.G. Pollach, W. Hein, A. Leitner, P. Zollner,Zuckerindustrie 127 (2002) 530–537.
80. G. Pollach, W. Hein, D. Beddie,Zuckerindustrie 129 (2004) 555–564.
81. H. Schiweck, L. Busching, Zucker 25 (1972)7–12.T. Cronewitz, H. Schiweck, R. Strauß,Zuckerindustrie 106 (1981) 127–135.
82. G. Haska, R. Nystrand, Sucr. Belge Sugar Ind.Abstr. 101 (1982) 131–144.R. Nystrand, Zuckerindustrie 110 (1985)693–698.
83. F. Schneider, E. Reinefeld, Zucker 13 (1960)460–471.
84. H. Schiweck, Zucker 24 (1971) 523–537.85. M. Shore et al., Int. Sugar J. 85 (1983) 6–10,
86. F. Schneider, Zucker Beihefte 1 (1950) 1.87. F. Schneider, E. Reinefeld, D. Schliephake,
Chem. Ing. Tech. 35 (1963) 567.88. G. V. Genie, Zuckerindustrie 104 (1979)
827–832.89. R. Pieck, W. Loop, Zucker 28 (1975) 236–241.90. H. Eichhorn, Zuckerindustrie 116 (1991)
329–358.91. F. Hollaus, G. Pollach, Zuckerindustrie 111
(1986) 1025–1030.92. K. Seidel, DT 824 929, 1949.
Simco Incorp., US 2 943 004, 1958 (E. E.Hanry).
93. IG-Farben Ind., DT 596 091, 1929 (K.Vierling).F. Uhde GmbH, DE 962 420, 1954 (G.Hingst). Sudzucker AG,Uhde GmbH, DE 1 139 800, 1959 (A. Bauer,R. Weidenhagen, H. Schiweck).
94. H. Bruniche-Olsen, Zucker 7 (1954) 471–475.95. M. Tyczewski, Zuckererzeugung 4 (1960) 250,
282, 317, 349, 377.
Sugar 71
96. P. Mathismoen, J. Ehrenberg, G. Lampe, S.Matusch, Zuckerindustrie 106 (1981)965–981.H. Luhrs, J. Ehrenberg, T. Rosmer, H. J.Krombach, Zuckerindustrie 112 (1987)571–581.
97. G. Witte, Zuckerindustrie 125 (2000) 311–322.98. R. F. Madsen, W. Kofod Nielsen, B.
Winstrom-Olsen, T. E. Nielsen, Sugar Technol.Rev. 6 (1978/79) 49–115.
99. G. Vaccari et al., Zuckerindustrie 117 (1992)724–728.
100. H. Schiweck, Zucker 29 (1976) 549–556.101. E. O. v. Lippmann, Dtsch. Zuckerind. 62
Sugar J. 47 (1985) 18–22;LC Listy Cukrov. 106 (1990) 176–186.E. Reinefeld, D. Miehe, Zuckerindustrie 113(1988) 15–20.R. F. Madsen, Zuckerindustrie 113 (1988)33–36.P. W. van der Poel, N. H. M. de Visser,Zuckerindustrie 113 (1988) 22–26,Zuckerindustrie 115 (1990) 943–949.
103. F. H. C. Kelly, D. W. Brown, Sugar Technol.Rev. 6 (1978/79) 1–46.F. Ledl, E. Schleicher, Angew. Chem. 102(1990) 597–626;Angew. Chem. Int. Ed. Engl. 29 (1990)565–594.
104. E. Reinefeld, K.-M. Bliesener, J. Schulze,Zuckerindustrie 107 (1982) 283–291,1111–1119.
105. F. A. Baczek, V. M. Jesic, Zucker 27 (1974)475–476. L. Busching,Zucker 30 (1977) 595–601.
106. De Danske Sukkerfabrikker, DT 917 663,1950.
107. Selwig & Lange Maschinenfabrik, DE 2 833348, 1978 (H. Ahlers, P. Mosel, S. Matusch).P. Mosel, S. Matusch, Zuckerindustrie 104(1979) 1033.S. Matusch, Zuckerindustrie 113 (1988)27–29.
114. H. Weidner, Zuckerindustrie 103 (1978)311–313.
115. O. Spengler, St. Bottger, Z. Ver. Dtsch. ZuckerInd. 83 (1933) 331.
116. F. Schneider, Zucker 12 (1959) 326.Braunschweiger Maschinenbauanstalt AG, DT921 980, 1952. F. Schneider, G. Fischer, G.Baumgarte DT 1 013 590, 1954;DT 1 043 979,1957.
117. F. Schneider, G. Baumgarten DT 1 048 840,1957. G. Schafer, Zuckerindustrie 115 (1990)371–375.
118. A. V. Brieghel-Muller: “Vortrag beim IX.Internat. Kongreß d. landwirtsch. Industrien inRom”, Z. Zuckerind. 2 (1952) 194.R. F. Madsen, Zuckerindustrie 113 (1988)33–36.
119. G. Quentin, Zucker 17 (1964) 336; 18 (1965)623.
120. G. Steinle, Zucker 25 (1972) 81.121. G. Witte, T. Cronewitz, Zuckerindustrie 113
122. S. Zagrodzki, A. Kubasiewicz, Sugar Technol.Rev. 5 (1977/78) 1–54.
123. K. Bohn: “Untersuchungen uber dieSaccharosezerstorung bei Temperaturen uber100 ◦C,” Vortrag bei der II. Int. Conf. on theChemistry and Technology of Sugar, Lodz,14–15 June, 1973. M. Athenstedt, Z.Zuckerind. 13 (1963) 563. K. Vukov, G.Patkai, Zuckerindustrie 106 (1981) 314. K.Vukov, I. Kormendy, H. M. Loko: Paperpresented at the 17. CITS-Conference,Copenhagen, 30 May–3 June, 1983.
124. H. Schiweck, Zuckerindustrie 116 (1991)793–805.
125. B. Morgenroth, H. Daschmann, K. Niepoth, G.Abker, B-C. Schulze, Zuckerindustrie 123(1998) 597–606.
126. K. Urbaniec: Modern Energy Economy in BeetSugar factories, 1st ed., Elsevier, Amsterdam1989.A. Baloh: Energiewirtschaft in derZuckerindustrie, vol. 1, Verlag Dr. A. Bartens,Berlin 1991.D. Schliephake, Zuckerindustrie 114 (1989)193–202.
72 Sugar
127. G. Trabanelli, G. Mantovani, F. Zucchi, SugarTechnol. Rev. 4 (1976/77) 131–208;Sugar Technol. Rev. 14 (1988) 1–28.
128. H. Schlegel, Z. Zuckerind. 13 (1963) 14.129. K. E. Austmeyer, Chem. Ing. Tech. 53 (1981)
716–719.130. D. Schliephake, Zucker 18 (1965) 138.131. L. J. Kuijvenhoven, I. J. Risseeuw, Int. Sugar
J. 85 (1983) 35–38.132. D. Schliephake, F. A. Orlowski, Chem. Ing.
Tech. 43 (1971) 676–682.133. K. E. Austmeyer, K. Kipke, Zuckerindustrie
105 (1980) 227–234.R. F. Madsen, Zuckerindustrie 105 (1980)234–237.P. W. van der Poel, Zuckerindustrie 105 (1980)237–240.L. Bachan, R. R. Sanders, Proc. SASTA 61(1987) 65–69.S. K. Helfels, E. J. de Jong, Chem. Eng. Tech.59 (1987) 443.
134. H. Thiele, A. Langen, Int. Sugar J. 76 (1974)136–146, 169–173.W. Bohm, Zucker 26 (1973) 21.D. Schliephake, K. E. Austmeyer, Zucker 28(1975) 546.
135. D. J. Radford, D. J. Tayfield, M. G. S. Cox,Int. Sugar J. 91 (1989) 52.
136. R. Hempelmann, K. E. Austmeyer,Zuckerindustrie 112 (1987) 695.
137. T. Frankenfeld, Zuckerindustrie 113 (1988)968.
138. G. V. Genie, Z. Zuckerind. 12 (1962) 557.139. Z. Bubnik, P. Kadlec, Zuckerindustrie 121
(1996) 36–39.140. H. Schiweck, M. Munir, G. Witte,
Zuckerindustrie 112 (1987) 681–693.K. E. Austmeyer, T. Frankenfeld,Zuckerindustrie 112 (1987) 36–45.
141. T. Kaga, Seito Gijutsu Kenkyu Kaiski 10(1961) 27–38.A. J. Gromkovskij, V. M. Fursov, Izv. Vyssh.Uchebn. Zaved. Pishch. Tekhnol. 4 (1977)157–162;Sugar Ind. Abstr. 39 (1977) 169.
142. E. A. Knøvl, G. R. Møller, Sugar Technol. Rev.3 (1975/76) 275–309.G. R. Møller, Int. Sugar J. 86 (1984) 73–79.
143. G. Witte, Zuckerindustrie 113 (1988) 414–420.P. Mentzel, P. Valentin, D. Wagner, G. Witte,Zuckerindustrie 115 (1990) 751–760. E. E. A.Rouillard:Proc. Annu. Congr. S. Afr. Sugar Technol.Assoc. 61 (1987) June.St. Jeschka, M. Lorenz, Zuckerindustrie 126(2001) 448–455.
144. M. Schneider, H. Schiweck, Zuckerindustrie111 (1986) 907–916.
145. K. E. Austmeyer, D. Schliephake, B. Ekelhof,G. Sittel, Zuckerindustrie 114 (1989)875–878.
146. O. Bia, Zuckerindustrie 112 (1987) 518–524.147. K. Helfels, A. Pot, C. H. de Nie, E. J. de Jong,
Zuckerindustrie 111 (1986) 845–850.148. H. Eichhorn, Zuckerindustrie 112 (1987)
793–804.150. H. Schiweck, Ind. Sacc. Ital. 73 (1980) 71–78.
R. A. Mc Ginnis, Sugar Technol. Rev. 5 (1978)155–286.R. F. Madsen, W. Kofod Nielsen, SugarTechnol. Rev. 7 (1979/80) 49–85.
151. D. Schliephake, B. Ekelhof, Zuckerindustrie108 (1983) 1127–1138.
152. G. Vaccari, M. Mantovani, G. Squoldino, D.Aquilano, M. Rubbo, Sugar Technol. Rev. 13(1986) 133–178.
153. J. O. Bara, S. Hashimoto, Sugar Technol. Rev.4 (1976/77) 209–258.J. C. Linden, Enzyme Microb. Technol. 4(1982) 130–136.
154. R. Mattes, K. Beaucamp, Chem. Unserer Zeit17 (1983) 54.
155. T. Cronewitz, Zucker 30 (1977) 662.W. Hunter, Int. Sugar J. 80 (1978) 358.
156. R. A. McGinnis, Sugar Technol. Rev. 5 (1978)155–286.G. Vavrinecz, Sugar Technol. Rev. 6 (1978/79)117–129.
157. G. Sittel, Zuckerindustrie 125 (2000) 501–507.158. T. Cronewitz, W. Jakel, K. Korn, Zucker 29
(1976) 230–237.159. K. E. Austmeyer, R. Marwede,
Zuckerindustrie 112 (1987) 193–201.A. Murphy, A. G. Punter, P. D. Thompson, Int.Sugar J. 93 (1991) 33–38, 52–55, 79–81, 86,95–96, 97–98.
160. K. W. R. Schonrock in K. Dorfner (ed.): IonExchanges in the Sweetener Industry in IonExchangers, De Gruyter, Berlin 1991.
161. A. Feldhoff, Zentralbl. Zuckerind. 15(1906/07) 1307.
162. E. W. Reed, J. S. Dranoff, Ind. Eng. Chem.Fundam. 3 (1964) 304.E. Berghofer, H. Klaushofer, L. Wieninger,Zucker 30 (1977) 187–203.
163. J. D. Phillips, A. Pollard, Nature (London) 171(1953) 41.
Sugar 73
164. J. Ponant, Sucr. Belge Sugar Ind. Abstr. 101(1982) 369–380.
165. W. Pannekeet, Ind. Aliment. Agric. 97 (1980)757.P. L. Mottard, Int. Sugar J. 85 (1983) 233–237.
166. Amalgamated Sugar Corp., US 3 982 956,1975 (K. W. R. Schoenrock, A. Gupta, H. G.Rounds).
167. G. Quentin, Zucker 7 (1954) 407; 10 (1957)408.
168. M. Kearney: “Simulated Moving BedTechnology Applied to the ChromatographicRecovery of Sucrose from Sucrose Syrups,”Proc. of the Sug. Processing Research Conf.,American Society of Sugar BeetTechnologists, Colarado Springs 1990, pp.291–304.V. J. Jaro, G. Pool, K. Schwarz:“Chromatographic Separator ExtractProcessing,” Proc. from the 26th BiennialMeeting of ASSBT, American Society of SugarBeet Technologists, Colarado Springs 1991,pp. 396–414.N. N., Zuckerindustrie 108 (1983) 636–638.H. G. Schneider, J. Mikule, Int. Sugar J. 77(1975) 259–264, 294–298.M. Munir, Int. Sugar J. 78 (1976) 100–106.
169. H. A. Paananen, Zuckerindustrie 122 (1997)28–33.
170. D. Costesso, G. Rearick, M. Kearney,Zuckerindustrie 125 (2000) 333–335.
171. H. Paananen, F. Rousset, Zuckerindustrie 126(2001) 601–604.
172. B. Ehrenhuber, Zuckerindustrie 130 (2005)463–469.
184. W. A. Ritschel: Die Tablette, Editio CantorKG, Aulendorf 1966.N. Pintauro: “Agglomeration Processes inFood Manufacture,” Food Processing Rev., no.25, Noyes Data Corp., Park Ridge, USA 1972.H. Schubert, Chem. Ing. Tech. 62 (1990)892–906.
187. European Economic Community, CouncilDirective of 11 Dec., 1973 (73/437/EC), Off. J.E. C. no L 356, 27.12.73, pp. 71–78;FirstCommission Directive of 26 July, 1979(79/786/EC), Off. J. E. C. no L 239, 22.9.79,pp. 24–52.
188. US Food Chemical Codex Standards-Sucrose57–50–1 Draft Nov. 1990. US Food ChemicalCodex Standards-Invert Sugar 8013–17–0Draft Feb. 1991.
189. N. Marignetti, G. Mantovani, Sugar Technol.Rev. 7 (1979/80) 3–47.R. D. Moroz, J. P. Sullivan, J. P. Troy, C. B.Broeg, Sugar Azucar 68 (1973) 46–52.
190. E. Thier, Zuckerindustrie 105 (1980) 80–82.191. FAO Food Nutr. Paper 38 (1988) 31–42.192. H. Schiweck, Dtsch. Lebensm. Rundsch. 76
(1980) 274–280.193. O. Mikus, L. Budicek, Sugar Technol. Rev. 13
(1986) 52–123.194. H. Schindler, B. Junckers, Zuckerindustrie 118
(1993) 103–106.195. W. Graup, S. Buhrmann, H. Will,
Zuckerindustrie 126 (2001) 331–335.196. F. Schneider, D. Schliephake, Zucker 14
(1961) 575.197. H. Schiweck, T. Cronewitz, G. Muller,
Zuckerindustrie 103 (1978) 185–190.198. E. Muhlack, U. Schroter, M. Kunz, W.
Glanser, Zuckerindustrie 105 (1980) 481–484.199. T. Cronewitz, G. Muller, B. Bissinger, F.
201. K. E. Austmeyer, W. Poersch, Zuckerindustrie108 (1983) 861–868, 1033–1041,Zuckerindustrie 109 (1984) 411–419,Zuckerindustrie 110 (1985) 28–34.W. Kunz, Zuckerindustrie 108 (1983)868–870.
202. P. Valentin, C. R. Assem. Gen. Comm. Int.Tech. Sucr. 18th (1987) 187–216.BMA: Zuckerindustrie 111 (1986) 357–358.
203. A. S. Jensen, J. Borreskov, D. K. Dinesen, R.F. Madsen, C. R. Assem. Gen. Comm. Int.Tech. Sucr. 18th (1987) 217–230;Zuckerindustrie 112 (1987) 886–891.A. S. Jensen, Zuckerindustrie 124 (1999)790–794, 125 (2000) 868–873.
204. A. Timmermans, Zuckerindustrie 126 (2001)185–187.
205. E. Muhlack, Zucker 23 (1970) 589–595.206. H. Schneidt, Sugar Technol. Rev. 3 (1975)
127–154.207. H. Schiweck, J. Henatsch, F. Curtius,
Zuckerindustrie 108 (1983) 835–847.208. G. F. Kroneberger, Sugar Technol. Rev. 4
(1976/77) 3–47.209. H. Schiweck, T. Cronewitz, F. Schoppe,
Zuckerindustrie 104 (1979) 813–819.210. A. P. Draycott: Sugar-Beet-Nutrition, Applied
Science Publ., London 1972, pp. 89–91.H. Irion: “Nahrstoff-Zusammensetzung undWirkung von Carbokalk auf Boden undPflanzen,” Proc. 51th IIRB-Winter-Congress,Brussels 1988, pp. 231–241.I. P. Vandergeten: “ Formes actuelles desvalorisation des ecumes des sucreries enEurope,” Proc. 51. IIRB-Winter-Congress,Brussels 1988, pp. 209–218.
211. E. M. Hartmann, Sugar Technol. Rev. 2 (1974)213–252.
212. R. Vandewijer, J. Jacques, R. Pieck, Sucr.Belge Sugar Ind. Abstr. 91 (1972) 187–197; 93(1974) 163–165.
213. J.-C. Giorgi, R. Gontier, B. Richard, Sucr. Fr.121 (1980) 93–101.W. Kofod Nielsen, S. Kristensen, R. F.Madsen, Sugar Technol. Rev. 9 (1982) 59–117.
214. W. Steinmetzer, Zuckerindustrie 116 (1991)30–39.
215. Suomen Sokeri, Finland, US 4 359 430, 1982.216. K. Sayama, T. Kamada, S. Oikawa, T. Masuda,
Zuckerindustrie 117 (1992) 894–898.217. J. E. Irvine in G. P. Meade, J. C. P. Chen (eds.):
Cane Sugar Handbook, 11th ed., J. Wiley &Sons, New York 1985, p. 13.
218. B. T. Egan, Proc. Queensl. Soc. Sugar CaneTechnol. 1964, 15–26.
219. B. T. Egan, Proc. Queensl. Soc. Sugar CaneTechnol. 1965, 25–30.
220. M. A. Clarke (ed.): Proc. Int. DextranWorkshop, Sugar Process. Res. Inc., NewOrleans 1984.
221. G. R. Shaw, G. A. Brotherton, Proc. Conf.Aust. Soc. Sugar Cane Technol. 1992, 1–7.
222. B. L. Legendre, Sugar J. 54 (1992) no. 2, 2–12.223. R. B. Trott: “Clarification and Decolorization
processes,” in M. A. Clarke, M. A. Godshall(eds.): Chemistry and Processing of Sugarbeetand Sugarcane, Elsevier, Amsterdam 1988,pp. 265–291.
224. M. A. Clarke, Sugar y Azucar Yearbook 1991,6–11.M. A. Clarke, Zuckerindustrie 121 (1996)505–510.
225. M. C. Bennett et al., Proc. Int’l. Soc. SugarCane Technol. (1977), 2797–2805.
226. J. B. Alexander, Proc. Congr. Int. Soc. SugarCane Technol. 14 (1971) 1619–1675.
227. M. A. Clarke, Sugar y Azucar 80 (1985)32–50.
228. O. Lyle: Technology for Sugar RefineryWorkers, Chapman and Hall, London 1941.
229. P. Carreno: “Symposium on Raw SugarQuality,” Proc. Sugar Ind. Technol. 52 (1993)95–174.
230. M. A. Clarke, Sugar y Azucar Yearbook 1983,71–93.
231. J. C. Abram, J. T. Ramage: “Sugar Refining:Present Technology and Future Development,”in G. G. Birch, K. J. Parker (eds.): Sugar:Science and Technology, Applied SciencePublishing, London 1979, pp. 49–96.
232. J. Dransfield, Principles 20 (1976) 83–90.233. H. J. Delavier, Z. Zuckerind. 17 (1967) 136.
G. Graefe in: Handbuch derLebensmittel-Chemie, vol. 5/1, SpringerVerlag, Berlin 1967, pp. 671 ff.
235. W. Mauch, E. Farhoudi, Sugar Technol. Rev. 7(1979/80) 87–171.
236. T. Cronewitz, W. Serkezy, Zucker 26 (1973)134–138.
Sugar 75
237. E. Hansen, Z. Lebensm. Unters. Forsch. 98(1954) 405–411.
238. H. Hallanoro, J. Ahvenainen, L.Ramm-Schmidt: “Saponin, a Cause ofFoaming Problems in Beet Sugar Processingand Use”, Proc. of the Sugar ProcessingResearch Conference, San Francisco 1990,174–201.M. A. Clarke, E. J. Roberts, M. A. Godshall,Zuckerindustrie 122 (1997) 873–877.K. K. Foong, R. Amal, W. O. S. Doherty, L. A.Edye, Zuckerindustrie 127 (2002) 382–388.
239. G. Steinle, E. Fischer, Zuckerindustrie 103(1978) 129–131.H. Schiweck, A. Kolber, Gordian 72 (1972)41–51.
240. P. X. Hoynak, G. N. Bollenback: This is LiquidSugar, Refined Syrups & Sugars, Yonkers,New York 1966, pp. 144, 148;Microbial Ecology of Foods, vol. 2, AcademicPress, New York 1980, pp. 779–803.
241. P. B. Koster et al., Zucker 28 (1975) 555–562;Zuckerindustrie 104 (1979) 49–53;Zuckerindustrie 106 (1981) 895–900.
242. P. B. Koster, Zuckerindustrie 103 (1978)200–203.
243. H. Schiweck, Branntweinwirtschaft 117(1977) 87–93.E. Sinda, E. Parkkinen: “Problems withMolasses in the Yeast Industry,” Symposium31 Aug.–1 Sept., 1979, Helsinki, Finland,Kauppakirjapaino oy Helsinki 1980.
244. H. Schiweck, C. Jeanteur-De Beukelaer, M.Vogel, Zuckerindustrie 118 (1993) 15–23.
245. R. Tressel, R. Jakob, T. Kossa, W. K. Bronn,Branntweinwirtschaft 116 (1976) 117.
246. E. Zauner, W. K. Bronn, H. Dellweg, R. Tressl,Branntweinwirtschaft 119 (1979) 154.W. K. Bronn, G. E. Kim, N. Fattohi,Branntweinwirtschaft 130 (1990) 134–144;Branntweinwirtschaft 131 (1991) 262–266.N. Fattohi, Zuckerindustrie 119 (1994)554–560,847–853.Zuckerindustrie 120 (1995) 587–592,677–682.
247. In [7] pp. 408–427.248. C. E. Moyer, Sugar J. 37 (1975) 20–23.
F. Cordovez, Sugar J. 45 (1983) 23.C. Mantovani, G. Vaccori, Sugar. J. 56 (1994)no. 12, 16–19.
249. J. M. Paturau: “By-products of the Cane SugarIndustry,” Sugar Ser., vol. 3, 2nd ed., Elsevier,Amsterdam 1982, pp. 76–119.
250. Suddeutsche Zucker-AG und IndustriewerkeKarlsruhe, DT 2 011 257, 1970 (T. Cronewitz,W. Portale, H. Schiweck, D. Lohmann).
253. J. Debruck, W. Lewicki, DeutscheZuckerrubenzeitung 18 (1982).
254. Liquid Ingredients Handbook NFIA, NationalFeed Ingredients Association, USA, 1975.
255. F. Hollaus, W. Braunsteiner, N. Kubadinow,Zuckerindustrie 108 (1983) 1049–1058.
256. V. Buckmann, Zuckerindustrie 124 (1999)519–521.
257. H. Bergner, E. Krieghoff, Dtsch. Landwirtsch.17 (1966) 546.
258. Pfeiffer & Langen, DE-AS 1 229 826, 1965.259. Bilder-Conversations-Lexikon fur das deutsche
Volk, vol. 4, F. A. Brockhaus, Leipzig 1841,817.
260. F. O. Licht: Jubilaumsausgabe, DieWeltzuckerwirtschaft 1936–1961, Selbstverlag,Ratzeburg 1962 pp. 42–45.F. O. Licht: Weltzuckerstatistik, Selbstverlag.,Ratzeburg 1962, 1968, pp. 14–18.A. Bartens/Mosolff: Zuckerwirtschaft–Europa2006, Verlag Dr. A. Bartens, Berlin 2006
261. U. Nohle, Zuckerindustrie 129 (2004)703–712.Supplement to Zuckerwirtschaft–Europa 2006,Verlag Dr. A. Bartens, Berlin 2006.
262. J. Berghauser, Ernahrungsumschau 28 (1981)422–425,figures changed according to letter of 09.03.93.
263. H. Schiweck, Zuckerindustrie 117 (1992)785–794.
