The Alcohol Alphabet 347

The Alcohol Alphabet

A glossary of terms used in the ethanol-producingindustries

Compiled by John E. Murtagh

A

Abbreviation for Angstrom.

Absolute ethanol A pharmaceutical term foranhydrous ethanol. It is generally defined ashaving less than 1% water.

Acetaldehyde Otherwise known as ethanal,acetic aldehyde or ethylaldehyde. A clearflammable liquid with a characteristic pungentodor. Chemical formula CH3CHO. Boils at21oC and freezes at -123.5oC. It is miscible inboth ethanol and water. It has a narcotic effecton humans, and large doses may cause deathby respiratory paralysis. It is a congener in theproduction of ethanol by fermentation, and isusually a major constituent of the headsfraction removed in rectification.

Acetic acid A colorless liquid with a pungentodor. Flammable at high concentrations.Chemical formula CH3COOH. Acetic acidmay be produced from ethanol by Acetobacterbacteria under aerobic conditions such aswhen a completed fermentation is agitated oraerated excessively.

Acetobacter A genus of Gram-negative, aerobicbacteria comprising ellipsoidal to rod-shapedcells as singles, pairs or chains. Otherwiseknown as acetic acid or vinegar bacteria, theyare able to oxidize ethanol to acetic acid. Theymay be responsible for loss of yield in ethanolproduction if a fermented mash is agitated oraerated excessively.

Acetone Otherwise known as 2-propanone,dimethyl ketone or pyroacetic ether. It is avolatile, very-f lammable liquid with acharacteristic pungent mousey odor and asweetish taste. Chemical formula CH3COCH3.Boils at 56.5oC and freezes at -94oC. It ismiscible with water, ethanol and most oils.Inhalation may cause headaches, and in largeamounts, narcosis. It is a congener in theproduction of ethanol by fermentation,particularly from molasses mashes. It is also aby-product of the production of butanol byanaerobic fermentation using the bacteriumClostridium acetobut ylicum. It tends toconcentrate in the heads fraction in therectification of neutral spirit.

Acid-acid process Term used in starch processingwhen acid hydrolysis is used to accomplish

Italic type denotes words (or minor variations of words) defined under separate entries.

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both the initial liquefaction and the finalsaccharification to simple sugars.

Acid-enzyme process Term used in starchprocessing when acid hydrolysis is used toaccomplish the initial liquefaction, and anenzyme such as amyloglucosidase is used forthe saccharification to simple sugars.

Acid hydrolysis The hydrolysis of a polymer bythe use of acid. In the case of starch hydrolysis,acids may be used as an alternative to enzymesin either (or both) the l iquefac tion orsaccharification processes.

Acid washing A process in which yeast recoveredfrom a finished fermentation is acidified toreduce the level of bacterial contaminationprior to recycling into a new fermentation.

Aguardiente An unaged alcoholic beverageproduced in Central and South America bythe distillation of beer derived from thefermentation of sugarcane juice or molasses.It is similar to crude rum.

Alcohol A member of a class of organiccompounds containing carbon, hydrogen andoxygen. Considered to be hydroxyl derivativesof hydrocarbons produced by the replacementof one or more hydrogen atoms by one ormore hydroxyl (OH) groups. Under theInternational Union of Pure and AppliedChemistry (IUPAC) naming system, the namegiven to an alcohol is derived from the parenthydrocarbon with the final e changed to ol.Thus methane-methanol, ethane-ethanol etc.The principal alcohol in fuel and beverage useis ethanol (otherwise known as ethyl alcohol.)

Alcohol Fuel Permit (AFP) A permit issued bythe Bureau of Alcohol, Tobacco and Firearmsallowing the holder to engage in theproduction of ethanol solely for fuel use.

Aldehyde A member of a class of organiccompounds considered to be derived by theremoval of hydrogen atoms from an alcohol.Aldehydes tend to be produced as congeners,or by-products of fermentation; and having alower boiling point than ethanol, they tend to

vaporize more readily and may accumulateas a heads fraction in the distillation process.

Alpha-amylase ("-amylase) An enzyme used inthe liquefaction of starch in the grain mashingprocess prior to saccharif ication andfermentation. "-amylase hydrolyzes the long-chain starch molecules into short-chain dextrins.These are more suitable for subsequentsaccharif ication by other enzymes tofermentable glucose. (" -amylase is anendoenzyme in that it works from the insideof the amylose molecule). In beveragealcohol production "-amylase may be derivedfrom malt (sprouted barley), but in fuel ethanolproduction the enzyme is obtained solely asa bacterial product. The enzyme moleculecontains a calcium atom, which is essentialfor its activity.

American Society for Testing and Materials(ASTM) A scientific and technical organizationwith headquarters in Philadelphia, PAestablished for the development of standardson characteristics and performance ofmaterials, products and services and thepromotion of related knowledge. It setsvoluntary consensus standards throughcommittees representing producers and users.ASTM has published standards for fuel ethanoland gasoline that have been adopted by manystates.

Amyl alcohol The principal constituent of fuseloil. Otherwise known as pentanol. Chemicalformula C5H11OH. Eight isomers exist, the mostcommon being primary isoamyl alcohol.

Amylase The name given to any enzyme thathydrolyzes (or breaks down) amylose, whichis a major component of starch.

Amyloglucosidase An enzyme, also known asglucoamylase, which hydrolyzes amylose intoits constituent glucose units. It is an exoenzymein that it works from an outer end of themolecule. It is normally used in conjunctionwith " -amylase for the liquefaction andsaccharification of starch in the grain mashingprocess, prior to fermentation. Amylo-glucosidase is a product of fungal growth.

The Alcohol Alphabet 349

Amylopectin A major component of starch(together with amylose). The molecule iscomposed of large, branched chains ofthousands of glucose units. The branching ofthe molecule distinguishes it from amylose andmakes it less-easily hydrolyzed into itsconstituent glucose units for fermentation.

Amylose A major component of starch (togetherwith amylopectin). The amylose molecule iscomposed of straight chains of hundreds ofglucose units. In the grain-mashing processfor ethanol production, amylose may first bebroken down into short-chain dextrins by a-amylase, which are in turn broken down intosingle glucose units by amyloglucosidase.

Anaerobic Literally means without air. Theopposite of aerobic. For example, yeastpropagation (or multiplication) is more rapidwith aeration (i.e., under aerobic conditions),while yeast produces ethanol under anaerobicconditions of fermentation.

Anaerobic digestion Process of breaking downwaste materials by anaerobic bac terialdegradation. Normally accompanied by theproduction of methane gas.

Angstrom () A unit of length equal to onehundred-millionth (10-8) of a centimeter, usedfor measuring the diameter of chemicalmolecules. Thus, in ethanol dehydration, amolecular sieve material with holes 3Angstroms in diameter may be used toseparate water, which has a 2.5 diameter,from ethanol, which has a 4.5 diameter.

Anhydrous Literally means without water. Theterm used for a substance that does notcontain water. Ethanol for fuel use iscommonly referred to as anhydrous, becauseit has had almost all of the water removed.See absolute ethanol.

Antibiotic A chemical substance produced bymicroorganisms with the capacity to inhibitgrowth or kill other microorganisms. Theantibiotic most commonly used in ethanolproduction is penicillin.

Antifoam (or defoamer) A preparationcomposed of substances such as silicones,organic phosphates and alcohols that inhibitsformation of bubbles in a liquid duringagitation by reducing the surface tension.Antifoam may be used in ethanol productionto control the development of foam infermenters. Antifoam may also be used tocontrol foam in beer distillation to increase thestripping capacity of a column.

Antiscalant (or scale inhibitor) A chemicalcompound or mixture of compounds addedto water or molasses beer to reduce theincidence of scaling in heat exchangers ordistillation columns. Usually, the principalingredients of antiscalants are chelatingcompounds.

Arabinose A pentose sugar comprising a majorconstituent of hemicellulose. Chemical formulaC5H10O5. It is not fermented by normal strainsof distillers yeasts. Also known as pectin sugaror gum sugar.

Archer Daniels Midland (ADM) Based inDecatur, IL. The largest US fuel ethanolproducer and a major producer of beverageand industrial alcohol.

Atomic weight The relative mass of an atombased on a scale in which a specific carbonatom (carbon 12) is assigned a mass value of12. Also known as relative atomic mass.

Azeotrope The term used to describe a constantboiling mixture. It is a mixture of two (or more)components with a lower boiling point thaneither component alone. For example water,which boils at 100oC, and anhydrous ethanol,which boils at 78.5oC, form a constant boilingmixture (azeotrope) at 78.15oC. The vapor ofthe mixture has the same composition as theliquid and therefore no further concentrationcan be achieved by normal distillation. Undernormal pressures it contains approximately97% by volume ethanol (1940 proof). It is veryexpensive in terms of energy to attempt toreach 1940 proof, so 1900 proof is generally

350 J.E. Murtagh

considered to be the practical, economicazeotrope limit for fuel ethanol distillation.

Azeotropic distillation A distillation process inwhich a liquid compound (entrainer) is addedto the mixture to be separated to form anazeotrope with one or more of thecomponents. Normally, the entrainer selectedis easily separated from the component to beremoved. For example, when benzene is usedin azeotropic distillation to dehydrate ethanol,the overhead condensate phase-separates toyield a water-rich layer that can be withdrawnand a benzene-ethanol layer which is refluxed.

B

Backset Recycled thin stillage. It may be addedto the cooker or to the fermenter and servesas a source of nutrients. It reduces the waterrequired for mashing and reduces the volumeof liquid residue to be evaporated. Improperlyhandled, it may be a major source of bacterialcontamination.

Bacteria Any of a large group of microscopicplants constituting the class Schizomycetaceaehaving round, rod-like, spiral, or filamentoussingle-celled bodies that are often aggregatedinto colonies, are often motile by means offlagella, and reproduce by fission or by theformation of asexual resting spores. They maylive in soil, water, organic matter or the livebodies of plants and animals. In ethanolproduction, bacteria are significant in that theycompete with yeast to ferment the availablesugars in a mash to products other than ethanoland cause losses in yield. However, somebacterial cultures may be added deliberatelyto rum fermentations to help produce certaindesired congeners. One genus of bacteria,Zymomonas, is being examined commerciallyfor its ability to ferment sugars to ethanol.

Bacterial contamination The conditionoccurring when undesirable bacteria become

established in a fermenting mash and reducethe ethanol yield. The bacteria use availablesugars to produce various compounds(congeners), particularly acids, which mayinhibit yeast activity. In severe situations,bacterial contamination may cause seriouseconomic losses.

Balling (or Brix) A scale used to measure thespecific gravity of a liquid in relation to that ofa solution of sugar in water. Each unit on thescale is equivalent to 1% by weight of sugar.Thus a mash of 20o Balling has the samespecific gravity as a 20% w/w sugar solution.The scale is frequently considered to indicate% dissolved solids in a liquid, although this isonly true of solutions of pure sugar.Traditionally, the term Balling has been usedin grain distilleries, while Brix has been usedin sugar mills and rum or molasses alcoholdistilleries. The measurement is accomplishedby use of a Balling (or Brix) hydrometer.

Barbet time See Permanganate time.

Bargeload Generally refers to a river barge witha capacity of 10,000 barrels or 420,000gallons.

Barrel A liquid measure equal to 42 US gallonsor 5.6 cubic feet. Or, a wooden container usedfor the aging and maturation of alcoholicbeverages. Barrels used for whiskeymaturation are made of oak wood and have acapacity of about 52 US gallons. Barrels mayonly be used once for aging bourbon whisky,so there is a worldwide trade in used bourbonbarrels for aging other alcoholic products suchas Scotch whisky and rum.

Base losses The percentage of ethanol lost inthe stillage at the base of a beer strippingcolumn or a rectifying column. It is virtuallyimpossible to achieve zero base losses, and itwould be wasteful of steam. The base lossesare generally monitored and controlled in anoptimal range determined by steam costs, etc.

BATF Abbreviation for US Bureau of Alcohol,Tobacco and Firearms.

The Alcohol Alphabet 351

Batch cooking Cooking a set amount of grainmeal, water and backset (if any) in a singlevessel as a discontinuous operation. One ormore batch cooks may be used to fill a singlebatch fermenter. Batch cooking is mainlyconfined to the beverage alcohol industry andsmaller plants in the fuel ethanol industry.

Batch distillation Distilling batches of beer in adiscontinuous operation. It is not commonlyused in fuel ethanol production, but is used inthe beverage ethanol industry particularly forthe production of special types of heavily-flavored distillates.

Batch fermentation The fermentation of a setamount of mash in a single vessel in adiscontinuous operation. In the ethanolproduction industries, batch fermentationpredominates over continuous fermentation.

Beer The name given to the product offermentation. In grain alcohol production beermay contain about 9-12% ethanol.

Beer preheater A heat-exchanging device usedfor heating beer before it enters a beer still.Usually, it also serves as the first condenserfor the beer still, so that the overhead vaporsheat the beer.

Beer still The distillation unit used for the initialremoval of ethanol from finished beer. Itgenerally consists of a stripping section thatextracts the ethanol from the beer and aconcentrating or rectifying section, whichnormally takes the ethanol up to 1900 proof(95o GL). Beer stills may consist of a single tallcolumn, or two or more columns standing sideby side, linked by vapor pipes.

Beer stripping column See Beer still.

Beer well The holding vessel into which finishedbeer is transferred prior to distillation.

Benzene Colorless, flammable, aromatichydrocarbon liquid. Chemical formula C6H6.Boils at 80.1OC and freezes at 5.4OC. Used asan entrainer for the dehydration of ethanol byazeotropic disti l lation. Known to becarcinogenic.

Beta-amylase (-amylase) An enzyme thathydrolyses the long-chain amylose moleculesin starch into fermentable maltose, the dimer(or double-molecule) of glucose. (It is anexoenzyme in that it works from an outer endof the molecular chain. It is found in malt(sprouted barley) in association with " -amylase. With the advent of microbialamyloglucosidase enzymes, malt amylases aregenerally only used in the production ofheavily-flavored beverage alcohol.

Betaglucan (-glucan) Gum-like polymers of-linked glucose as in cellulose instead of the"-linked glucose units as in starch (amylose).Betaglucan is commonly present in barleymashes. It is not broken down by "-amylaseand causes foaming problems due to itsviscous elastic nature.

Betaglucanase (-glucanase) An enzyme whichhydrolyses betaglucan. It is frequently used inbarley mashing to reduce foaming andviscosity problems.

Beverage alcohol Any form of distilled ethanolwith or without congeners considered by lawto be fit for human consumption. The laws inmany countries confine beverage alcohol tothat produced by fermentation as opposed toalcohol of synthetic origin.

Binary azeotrope An azeotrope or constantboiling mixture having two components suchas ethanol and water.

Bio-ethanol See fermentation ethanol.

Bio-gas The gas produced by anaerobic digestionof wastes. It is mainly methane.

Biological oxygen demand (BOD) A measureof the oxygen-consuming capacity of organicmatter contained in ef f luents. Duringdecomposition, organic effluents have anoxygen requirement that may deplete thesupply in a waterway and result in the deathof fish and other aquatic life. BOD is normallymeasured on the basis of the weight of oxygenrequired per unit volume of an effluent.

352 J.E. Murtagh

Biomass Any renewable organic matter suchas agricultural crops, crop waste residues,wood, animal and municipal wastes, aquaticplants, fungal growth, etc.

Blackstrap See molasses.

Blended whisky Defined by the US Bureau ofAlcohol, Tobacco and Firearms as a mixturecontaining at least 20% of straight whisky ona proof gallon basis, together with otherwhiskies or neutral spirits. When a blendcontains more than 51% of a straight whisky,it may be designated by that specific type, suchas blended rye whisky.

Blender Tax Credit A US federal income taxcredit granted to blenders of ethanol andgasoline as an alternative to the excise taxexemption. It was originally introduced underthe Crude Oil Windfall Profits Tax Act of 1980,at a level of 40 cents per gallon, and wassubsequently raised to 50 cents by the SurfaceTransportation Assistance Act of 1982, and to60 cents by the Deficit Reduction Act of 1984.

BOD (See Biological Oxygen Demand)

Boiler efficiency The thermal efficiency of aboiler in terms of the usable energy output (inthe form of steam) in relation to the energyinput in the form of fuel. Boiler efficienciesare commonly in the 70-80% range.

Boiling point The temperature at which thetransition occurs from the liquid to the gaseousphase. In a pure substance at a fixed pressurethe boiling point does not vary.

Bourbon whisky Defined by the BATF as whiskyproduced at not more than 1600 proof from afermented mash of not less than 51% corn,and stored at not more than 1250 proof incharred, new oak barrels. In practice, thebourbon whisky mash bill is frequently about65% corn, 25% rye, and 10% barley malt.

Brandy Defined by the BATF as an alcoholicdistillate from the fermented juice, mash orwine of fruit, or from the residue thereof,produced at less than 1900 proof, in such a

manner that the distillate possesses the taste,aroma and characteristics generally attributedto the product.

British Thermal Unit (BTU) The amount of heatrequired to raise the temperature of onepound of water one degree Fahrenheit underdefined pressure conditions. It is the standardunit for measuring heat energy in the US.

Brix See Balling.

BTU Abbreviation for British Thermal Unit.

BTX Abbreviation for the three related octaneenhancers, benzene, toluene and xylene.

Bubble cap A contacting device used on somedistillation plates. It consists of a cylindricalchimney set in a hole in the plate and coveredby a dome-shaped cap, which deflects thevapors rising up the chimney to cause themto pass through the liquid layer on the plate.

Bureau of Alcohol, Tobacco and Firearms(BATF) An agency of the US Department ofthe Treasury entrusted with enforcing lawscovering the production, distribution and useof alcohol, tobacco and firearms.

Bushel A unit of dry volume equal to 2150.42cubic inches or 1.244 cubic feet. When usedto measure grain, bushel weight depends onthe type and condition of the grain. In thecase of corn, bushel volume generally averagesabout 56 lbs by weight. This has led to theuse of a distillers bushel, which represents 56lbs of grain, regardless of type or volume.

Butanol (butyl alcohol) A minor constituent offusel oil. Chemical formula C4H9OH. Fourisomers exist. They are all colorless, toxicf lammable liquids. n-Butanol may beproduced as a co-product with acetone andethanol by the fermentation of selectedcarbohydrates with the anaerobic bacteriumClostridium acetobutylicum. Butanols are usedas solvents and chemical intermediates.

By-products Products that are secondary to theprincipal product of a process. In ethanolproduction, carbon dioxide and distillers dried

The Alcohol Alphabet 353

grains are normally considered by-products;but in certain circumstances they may beviewed as co-products, in that they maycontribute significantly to the overall processeconomics.

C

Carbohydrate Any of a group of compoundscomposed of carbon, hydrogen and oxygenincluding the sugars, starches, dextrans andcelluloses. They are the most abundant classof organic compounds in nature, constitutingapproximately 75% of the dry weight of allvegetation.

Carbon dioxide A colorless non-flammable gas.Composition CO2. It does not support humanrespiration; and in high concentrations itcauses asphyxiation. It is approximately 1.5times the weight of air, and tends toaccumulate in floor drains, pits and in thebottoms of unventilated tanks. It is producedby various means, notably the combustion offuels in an excess of air and is a by-product ofyeast fermentation. It may be recovered fromfermentations and compressed to a liquid orsolid (dry ice).

Carbon monoxide A colorless, odorless,flammable gas (coal gas). Composition CO.It is poisonous if inhaled, as it combines withblood hemoglobin to prevent oxygen transfer.It is very slightly lighter than air. It is producedby the incomplete combustion of fuels with alimited oxygen supply, as in auto engines. It isa major component of urban air pollution,which can be reduced by blending an oxygen-bearing compound (or oxygenate) such asethanol into hydrocarbon fuels.

Carbon steel A steel deriving its particularproperties from its content of carbon. Thesesteels may range from low-carbon, (havingless than 0.25% carbon), to high-carbon).Low carbon or mild steel is easily hot-worked

and rolled, and is used in steel plates andbeams. It is easily welded, but is readily subjectto rusting and other forms of corrosion.

Caribbean Basin Initiative (CBI) The programarising from the Caribbean Basin EconomicRecovery Act passed by the US Congress in1983 to encourage industrial development inthe Caribbean islands and Central America.Under this program, fuel ethanol and otherproducts from the region may enter the USwithout being subject to customs duties.

Cassava A root crop with a high starch contentgrown in the tropics and subtropical regions.Known in Brazil as manioc, it is used as analternative to sugarcane as a feedstock forethanol production. It is also processed forfood as tapioca.

CBI Abbreviation for Caribbean Basin Initiative.

CCC Abbreviation for Commodit y CreditCorporation.

CDA Abbreviation for completely denaturedalcohol.

Cell recycle The process of recovering yeast fromfermented beer to return it to the starting vesselof a continuous fermentation or to a new vesselin a batch fermentation system. It may includean acid washing step to reduce bacterialcontamination.

Cellulase An enzyme capable of hydrolyzinglong-chain cellulose molecules into simplesugars or short-chain polymers.

Cellulose The principal polysaccharide in livingplants. It forms the skeletal structure of thecell wall, hence the name. It is a polymer ofglucose units coupled by -type linkages intochains of 2,000-4,000 units. Cellulose normallyoccurs with other polysaccharides andhemicelluloses derived from sugars such asxylose, arabinose and mannose.

Celsius (or centigrade) A temperature scale inwhich (at normal atmospheric pressure) waterfreezes at zero degrees and boils at 100degrees.

354 J.E. Murtagh

Centrifugal pump A machine for moving liquidsby accelerating them radially outwards bymeans of a rotating impeller contained withina casing. It is the most common and mostversatile type of pump in normal industrial use.It has an advantage in that it does not force apositive displacement of liquids, so it may beused in systems where output must bethrottled or completely closed by controlvalves. This feature makes centrifugal pumpsunsuitable for moving heavy viscous liquidssuch as molasses and syrups.

Centrifuge A machine for separating insolubleliquids or solids from liquids by the applicationof centrifugal force. The two main types ofcentrifuges are filter and sedimenter. Infiltering centrifuges, solids are retained in arotating perforated basket while liquid passesthrough the perforations. In sedimentingcentrifuges, the mixture is thrown against asolid-walled cylinder and the heavier solidparticles collect against the wall for removalwhile the lighter liquid collects in the centralpart. Centrifuges are commonly used inethanol plants for yeast recovery and in stillagedewatering.

Chemical oxygen demand (COD) A laboratorytest to determine the oxygen requirements forthe chemical digestion of effluents. It shouldbe distinguished from the BOD test, whichdetermines the total of both chemical andbiological oxygen requirements. COD ismeasured in a rapid test that involves heatingthe effluent in the presence of an oxidizingagent such as potassium dichromate and thendetermining the amount of oxygen absorbedby the effluent.

Chlorine dioxide Chemical formula ClO2. It isa strongly-oxidizing, yellow-to-reddish-yellowgas at room temperature. It has an unpleasantodor similar to that of chlorine and reminiscentof nitric acid. It is unstable in light. It reactsviolently with organic materials and is easilydetonated by sunlight or heat inconcentrations greater than 10% at atmos-pheric pressure. Boils at 11oC and freezes at

-59oC. Chlorine dioxide may be used as asterilant, and may be produced in situ forsterilizing yeast mashes by addition of sodiumchlorite solution in the presence of acids orchlorine (or hypochlorite solution). It isconsiderably more effective as a sterilant thanstraight chlorine.

Chromatography A method for separating amixture of chemical compounds intoindividual components by selectivedistribution between two immiscible materials(or phases), one stationary and the othermobile. The phases are selected so that themobile phase will carry the variouscomponents through the stationary (or solid)phase at differing rates to give separation. Gaschromatography may be used to separateethanol from the other congeners producedin fermentation and to measure themquantitatively. High performance liquidchromatography may be used to follow starchhydrolysis in grain alcohol production.

CIP Abbreviation for cleaning-in-place system.

Citrus molasses A by-product of the citrus juiceindustry. Citrus residue, mainly peel, is treatedwith lime and then passed through a press.The press liquor is then evaporated to aviscous, dark brown molasses of about 72o Brix.Citrus molasses is similar to cane blackstrapmolasses, having about 45% total sugars.However, it has more protein and a muchlower ash content. Citrus molasses may bediluted and fermented for ethanol production,but it may need pretreatment to reduce thecontent of d-limonene (commonly referred toas citrus-stripper oil), which tends to inhibityeast growth.

Cleaning-in-place system (CIP) A systemdesigned to permit process equipment to becleaned without disconnecting or dismantling.A sophisticated automatic CIP system mayprovide a sequence of water flushing cycles,detergent washing and chemical sterilizing ofequipment at the press of a button.

The Alcohol Alphabet 355

Closed receiver (See Receiver.)

CMS Abbreviation for condensed molassessolubles.

Coccus (plural: cocci) A type of bacteria withspherically-shaped cells. They may occur assingle cells, clusters or long chains.

COD Abbreviation for chemical oxygen demand.

Column A vertical cylindrical vessel containinga series of perforated plates or other contactdevices through which vapors may pass toeffect a separation of liquid mixtures bydistillation.

Co-mingled tank The term used for fuel ethanoltanks at refineries or pipeline terminals wheretwo or more suppliers may share the sametank for storing ethanol.

Commodity Credit Corporation (CCC) Anagency of the USDA established to stabilizeand protect farm incomes and prices bymaintaining balanced and adequate suppliesof agricultural commodities.

Completely denatured alcohol (CDA) A termused by the BATF to describe ethanol madeunfit for human consumption by addition ofspecified denaturants such as methyl isobutylketone, kerosene or gasoline.

Concentrating column A column where hydrousethanol is concentrated to decrease watercontent. A beer still may consist of a strippingcolumn in which dilute ethanol is removedfrom beer and a concentrating column, whichreceives ethanol vapor from the strippingcolumn and concentrates it up to about 1900

proof (95oGL). If provision is made in aconcentrating column to remove impuritiessuch as fusel oil, then it is more correctly arectifying column.

Condensate Liquid condensed from vapor in acondenser.

Condensed molasses solubles (CMS) The termused to describe molasses sti l lageconcentrated by evaporation. The molassesresidue (after fermentation and distillation)

may be concentrated to about 60o Brix (orapproximately 60% solids) to be sold as asubstitute for molasses in animal feeds as acaking agent and dust suppressant. It containshigh concentrations of salts.

Condenser A heat exchange device connectedto the vapor discharge pipe of a column topermit the vapor to be cooled and condensedto a liquid. Condensers are commonlycylindrical vessels containing tubes throughwhich cooling water is passed.

Congeners Chemical compounds producedwith ethanol in the fermentation process. Theyare frequently referred to as impurities.Common congeners are methanolacetaldehyde, esters (such as ethyl acetate) andfusel oils (higher alcohols, particularly amylalcohols.) Fermentation conditions may beadjusted to control congener formationdepending on the requirements for the endproduct.

Constant boiling mixture See Azeotrope.

Continuous cooker A system into which a mashof water, grain and enzymes may be fedcontinuously to be cooked and discharged tothe fermentation system. Continuous cookersgenerally consist of a slurry tank connectedby a pump to a steam jet heater, a holdingvessel or lengths of piping (to provide someresidence time at the cooking temperature),one or more flash vessels (to cool the cookedmash), a holding vessel for enzymaticliquefaction and a heat exchanger for finalmash cooling. Continuous cookers are morecommon in fuel ethanol plants than inbeverage alcohol plants.

Continuous fermentation A system into whichcooked mash may be fed continuously to befermented and then discharged to the beerwell and distillation system. Continuousfermentation systems generally consist of aseries of interconnected tanks sized to providesufficient residence time for the fermentationto proceed to completion. The ethanolindustry is divided on fermentation systems,

356 J.E. Murtagh

with more gallonage produced by batchfermentation than by continuous fermentation.

Continuous distillation A process usingspecially-designed equipment to permit avolatile component such as ethanol to beseparated by distillation from a continuousflow of an aqueous solution such as beer.

Control loop A portion of a process controlsystem that includes a sensing deviceconnected to a signal transmitter, a controller,another signal transmitter and an actuator. Forexample, a pressure control loop on adistillation column may have a pressure sensorconnected through a controller to a steam flowregulating valve.

Cooker A device for heating a slurry of grainand water to a sufficiently-high temperaturefor sufficient time to release and gelatinize thestarch in the grain and thereby render itsusceptible to enzymatic hydrolysis. Live steamis normally used for heating the slurry; andpumps or agitators are used to ensure mixingand even heating. Cooking may be performedcontinuously or in a batch mode.

Cooling tower A tower or other type of structurewhere air (the heat receiver) circulates in director indirect contact with warmer water (theheat source) to cool the water. Cooling towersare used in ethanol production plants torecirculate cooling water and to minimize theamount of water used from wells, rivers orpublic sources.

Cooper A person who makes or repairs woodenbarrels.

Cooperage A place where wooden barrels aremade or repaired. Also used to refer to asupply of barrels (i.e., the product of the workof a cooper).

Co-products Where the economics of aproduction process depend on the value ofmore than just the primary product, thesecondary products are referred to as co-products rather than as by-products. Forexample, disti l lers dried grain may be

considered a co-product of the production ofethanol from dry milled grain.

Cordials See liqueurs.

Corn steep liquor The sulfurous liquid that hasbeen used for steeping and softening cornprior to wet milling. It contains extractednutrients and serves as a nutrient source insubsequent fermentation of the starch stream.

Corn whisky Defined by the BATF as whiskyproduced at under 1600 proof from afermented mash containing not less than 80%corn grain. If corn whisky is stored in oakbarrels, the BATF stipulates that the proofshould not be more than 125o, and that thebarrels be used, or uncharred if new.Furthermore, the whisky cannot be subjectedto any treatment with charred wood.

Corrosion The destruction, degradation ordeterioration of material (generally metal) dueto the reaction between the material and itsenvironment. The reaction is generallychemical or electrochemical, but there areoften important physical and mechanicalfactors in the corrosion process.

Corrosion inhibitor A substance that reducescorrosion. For example, corrosion-inhibitingcompounds may be added to fuel ethanol(particularly methanol) to reduce corrosion oftanks and automobile engine parts.

Co-solvent A liquid required to keep anotherliquid in solution in a third liquid. For example,in the Dupont Waiver for the use of 5%methanol in gasoline, 2.5% ethanol (or a higheralcohol) is required as co-solvent to improvethe miscibility of the methanol in the gasoline.

Crude Oil Windfall Profits Tax Act of 1980 USfederal legislation that extended to 1992 theexcise tax exemption for ethanol-gasolineblends granted under the Energy Tax Act of1978. It also introduced a blender tax creditof 40 cents per gallon of ethanol as analternative to the excise tax exemption.

Cyclohexane A colorless, flammable, alicyclichydrocarbon liquid of chemical formula C6H12,

The Alcohol Alphabet 357

that boils at 80.3oC, and freezes at 6.5oC. It isused as an alternative to benzene as anentrainer in the dehydration of ethanol byazeotropic distillation.

D

DDG Abbreviation for distillers dried grain.

DDGS Abbreviation for distillers dried grain withsolubles.

DE Abbreviation for dextrose equivalent.

Deadleg A length of mash piping closed eithertemporarily by a valve, or permanently to leavea dormant pocket of mash that may becomea source of bacterial contamination.

Dealer tank wagon (DTW) Used in referenceto fuel ethanol and gasoline sales, it is generallyof 7,000-8,000 gallons capacity.

Decanter Vessel used for the separation of two-phase liquids. In a fusel oil decanter, an upperfusel oil phase is separated from a loweraqueous ethanol phase. In a benzene columnreflux decanter, the upper, mainly-benzene,phase is separated from the lower, mainly-water, phase.

Deficit Reduction Act of 1984 US federallegislation that increased the excise taxexemption on ethanol-gasoline blends from 5cents (as set by the Surface TransportationAssistance Act of 1982) to 6 cents per gallon.It also increased the alternative blender taxcredit to 60 cents per gallon of ethanol.

Defoamer See Antifoam.

Dehydration The process of removing waterfrom a substance, particularly the removal ofmost of the remaining 5% of water from 1900

proof ethanol in the production of absolute oranhydrous ethanol.

Demethylizing column Occasionally referredto as a supplementary column, it is a

fractionating column used to remove methanolin the production of neutral spirit and is locatedafter the rectifying column. The demethylizingcolumn is heated indirectly via a reboiler. Theimpure spirit enters part way up the columnand the methanol is removed in the overheadvapor together with some ethanol, while thebulk of the ethanol descends to be removedat the base of the column as a productrelatively free of methanol.

Denaturant A substance added to ethanol tomake it unfit for human consumption so thatit is not subject to taxation as beverage alcohol.The BATF permits the use of 2-5% unleadedgasoline (or similar, specified substances) foruse as denaturants for fuel ethanol. (See alsospecially-denatured alcohol)

Department of Energy (DOE) A department ofthe US federal government established in 1977to consolidate energy-orientated programs andagencies. The departments mission includesthe coordination and management of energyconservation, supply, information dissemi-nation, regulation, research, development anddemonstration. The department includes anOffice of Alcohol Fuels.

Dephlegmator Name commonly used for thefirst of two or more condensers attached tothe overhead vapor line of a distillation column.It literally means an entrained liquid separator.

Desiccant A substance that absorbs water andcan be used for drying purposes. For example,potassium aluminosilicate is used as a desiccantin molecular sieve systems for ethanoldehydration.

Detergent package A combination of detergentsand corrosion inhibitors normally added to fuelethanol to impart a cleaning action to ethanol-gasoline blends and thereby reduce engine fuelinjector blockages.

Dewatering The removal of water (or otherliquids) from a solid material, particularly theuse of screens or centrifuges in the initialseparation of thin stillage (liquid) from the

358 J.E. Murtagh

solids contained in whole stillage in DDGprocessing.

Dextran A non-fermentable, large, branched-chain polymer of sucrose molecules producedin molasses by bacterial contamination (mainlyLeuconostoc mesenteroides). It gives a ropeyappearance to molasses when stirred orpoured, and reduces ethanol yield onfermentation.

Dextrin Short-chain polymers of glucosemolecules produced by the partial hydrolysisof starch with "-amylase or acid in the initialstage of conversion to fermentable sugars.

Dextrose An alternative name for glucose.

Dextrose equivalent (DE) A measure of thedegree of hydrolysis of starch. It is no longerconsidered as significant as previously inethanol production with the more generalacceptance of simultaneous saccharificationand fermentation.

Diethyl ether The traditional anaesthetic ether,which is employed as an entrainer in someazeotropic distillation processes for fuelethanol dehydration (as an alternative to themore commonly-used benzene). It is acolorless, flammable liquid that boils at 34.6oCand freezes at -117oC. Chemical formula(C2H5)2O. It readily forms explosive mixtureswith air.

Differential pressure cell (DP cell) A devicefor measuring the difference in pressure ofliquid on either side of a restricting orifice. Itis used in flow measurement. (See Orificemeter).

Dimer A compound produced by linkingtogether two molecules of a simplercompound (or monomer). It is the simplestform of polymer. For example, maltose is adimer composed of two linked glucosemolecules.

Disaccharide A compound sugar that yields twomonosaccharide units on hydrolysis. Forexample, lactose yields glucose and galactose,

sucrose yields glucose and fructose, whilemaltose yields two glucose units.

Disc and donut column A beer distillationcolumn patented by Raphael Katzen with traysalternately consisting of annular shelves withopen centers (donuts) and discs (of a slightlylarger diameter than the donut holes) placedcentrally below the holes. The effect is to givea circular curtain of liquid descending fromtray to tray, through which the rising vaporsmust pass. It has the advantage of beingunaffected by the solids content of the beerfeed or any scaling that may occur in a typicaltray column.

Distilland Material to be distilled, such as beer.

Distillate The portion of a liquid (distilland)removed as a vapor and condensed during adistillation process.

Distillation The process by which thecomponents of a liquid mixture are separatedby differences in boiling point by boiling andrecondensing the resultant vapors. In ethanolproduction, it is the primary means ofseparating ethanol from aqueous solutions.

Distilled spirits permit (DSP) A permit issuedby the BATF allowing the holder to engage inthe production or warehousing ofundenatured ethanol for beverage, industrialor fuel use.

Distillers bushel 56 lbs of any grain, regardlessof volume.

Distillers dried grain (DDG) The dried residualby-product of a grain fermentation process. Itis high in protein, as most of the grain starchhas been removed. It is used as an animalfeed ingredient. By strict definition, DDG isproduced only from the solids separated fromwhole stillage by centrifuging or screening. Inpractice, the term is commonly used todescribe the entire dried stillage residue,making it synonymous with DDGS.

Distillers dried grain with solubles (DDGS) Theproduct derived by separating the liquid

The Alcohol Alphabet 359

portion (thin stillage or solubles) from grainwhole stillage by screening or centrifuging, thenevaporating it to a thick syrup and drying ittogether with the grain solids portion.

Distillers dried solubles The product derivedfrom separating the liquid portion (thin stillage)from grain whole stillage, evaporating it to athick syrup and then drying it to a fine powder.

Distillers feeds The by-products of fermentationof cereal grains. See DDG and DDGS.

Distillers Feeds Research Council Anorganization established in 1945 to fund andcoordinate universit y research into theutilization of DDG.

Distillers wet grain (DWG) The wet grainresidue separated from whole stillage byscreening or centrifuging. It has a very limitedstorage life and is generally used only wherecattle feedlots are located near ethanolproduction plants.

Distillery A building or premises where alcoholis distilled.

Distillery run barrels Recently-emptied, usedwhiskey barrels that have not been sorted toremove those with or without defects.

DMA 67Y A detergent produced by Dupont. Itis added to fuel ethanol to ensure that theresultant blend with gasoline will have clean-burning characteristics similar to detergentgasolines supplied by major oil companies.

Downcomer (or downpipe) A device used indistillation columns to allow liquid to descendfrom one plate to another. Downcomers maytake the form of one or more round, oval orrectangular section pipes, or chordal baffles.The downcomer usually has a weir-type sealat the bottom to prevent vapors passingupward.

DP cell. See differential pressure cell.

Dry degermination A process for the removalof germ from grain without the need forsteeping and wet milling. It may involve somepretreatment of the grain to raise the moisturecontent before processing. It is used in

Scotland for corn milling in grain whisky plantsand is used in the production of corn flakes;but is not commonly used in the US ethanolproduction industry.

Dry milling In the ethanol production industrydry milling refers to the milling of whole drygrain where, in contrast to wet milling, noattempt is made to remove fractions such asgerm and bran. It may be carried out withvarious types of equipment, including hammermills and roller mills.

DSP Abbreviation for Distilled Spirits Permit.

DTW Abbreviation for Dealer Tank Wagon.

Dual-flow plate (or tray) A perforated platesimilar to a sieve plate, without downcomers.The perforations are of such a size and openarea that the liquid descends by weepingthrough the holes.

Dunder A Caribbean synonym for vinasse ormolasses stillage. It is commonly used to referto vinasse that has been stored for some timeto allow bacterial development prior to beingused as backset in the production of heavily-flavored rums.

Dupont waiver The waiver received by Dupontfrom the EPA in 1985 for a blend of gasolinecontaining a maximum of 5% methanol plusa minimum of 2.5% ethanol or other approvedco-solvent , together with an approvedproprietary corrosion inhibitor.

DWG Abbreviation for distillers wet grain.

E

ED Abbreviation for extractive distillation.

Effect In the context of evaporators, the term isused to describe one vessel in a series. Forexample a quadruple effect evaporator consistsof four linked vessels.

EITC Abbreviation for energy investment taxcredit.

360 J.E. Murtagh

Endoenzyme An enzyme acting on internalportions of a large polymeric molecule ratherthan around the periphery. For example, the"-amylase enzyme hydrolyzes linkages withinamylose and amylopectin molecules. Incontrast, amyloglucosidase acts as anexoenzyme by only hydrolyzing the outermostlinkages.

Energy investment tax credit (EITC) A 10%income tax credit for investments inequipment for the production of fuels such asethanol from biomass. This credit wasoriginally introduced under the Energy Tax Actof 1978, modified and extended under theCrude Oil Windfall Profits Tax Act of 1980 andfinally phased out in 1987 under the Tax-Reform Act of 1986.

Energy Policy Act of 1992 US federal legislationthat amended the provisions of the OmnibusReconciliation Act of 1990 to allow theproration of the excise tax exemption of 5.4cents per gallon on ethanol gasoline blendsthat use less than the standard content of 10%ethanol. This was to meet the requirementsof the Clean Air Amendments Act thatrequired that oxygenate blends with 2.1% or2.7% oxygen be used in gasolines indesignated areas suffering from severe airpollution. (These oxygen rates correspond toethanol usages of 6% and 7.7%, respectively.)

Energy Security Act of 1980 US federallegislation that supported the emerging fuelethanol industry by establishing anindependent Office of Alcohol Fuels within theDepartment of Energy and authorizedprograms of loan guarantees, price guaranteesand purchase agreements with fuel ethanolproducers.

Energy Tax Act of 1978 US federal legislationthat instituted the first excise tax exemption forgasoline blended with 10% fermentationethanol. It exempted the blends from the taxof 4 cents per gallon. It also created an energyinvestment tax credit (EITC) of 10% thatapplied to equipment for converting biomass

to ethanol in addition to the standard 10%investment tax credit.

Entrainer A substance used to assist in thedehydration of ethanol by azeotropicdistillation. Examples are benzene, cyclo-hexane and pentane. (See azeotropicdistillation.)

Environmental Protection Agency (EPA) A USgovernment agency established in 1970. EPAresponsibilities include the regulation of fuelsand fuel additives, including ethanol gasolineblends.

Enzymatic hydrolysis The hydrolysis of a polymerby the use of enzymes. In the case of starchhydrolysis, an "-amylase enzyme may be usedin the initial hydrolysis to achieve liquefactionand an amyloglucosidase enzyme may be usedto complete the hydrolytic saccharification tofermentable sugars.

Enzyme Any of a class of complex proteinaceoussubstances (such as amylases and lactases)produced by living organisms that catalyzechemical reactions without being destroyed.Enzymes may act outside the producingorganism and maybe used in industrialprocesses such as saccharification.

EPA Abbreviation for Environmental ProtectionAgency.

Ester The product derived by the reaction of anacid with an alcohol or other organiccompound having hydroxyl groups. Forexample, ethyl acetate is an ester producedby reacting acetic acid with ethanol. Esters tendto accumulate in distillation in the heads atthe top of the column.

ETBE Abbreviation for ethyl tertiary butyl ether.

Ethanol Otherwise known as ethyl alcohol,alcohol, grain-spirit or neutral spirit, etc. A clear,colorless, flammable oxygenated hydrocarbon.Chemical formula: C2H5OH. It has a boilingpoint of 78.5oC in the anhydrous state.However, it forms a binary azeotrope withwater with a boiling point of 78.15oC at acomposition of 95.57% by weight ethanol.

The Alcohol Alphabet 361

Ether One of a class of organic compounds inwhich an oxygen atom is interposed betweentwo carbon atoms in the molecular structure.Ethers may be derived from alcohols by theelimination of water. Ethers such as diethylether and isopropyl ether may be used asentrainers in the dehydration of ethanol byazeotropic distillation. Other ethers such asMTBE and ETBE may be used as octaneenhancers in gasoline. Ethers are dangerousfire and explosion hazards. When exposedto air they form peroxides that may detonateon heating.

Ethyl acetate Chemical formula CH3COOC2H5.A clear, volatile, flammable liquid with acharacteristic fruity odor. It has a pleasant,sweet taste when diluted. Boils at 77oC andfreezes at -83oC. It is produced by the reactionof ethanol with acetic acid and is a majorcomponent of the esters that give rum itscharacteristic odor.

Ethyl alcohol See Ethanol.

Ethyl carbamate Otherwise known as urethaneor carbamic acid ethyl ether. A carcinogeniccompound produced by heating urea withethanol under pressure. Chemical formulaNH2COOC2H5. It is very soluble in ethanolor water. Traces of ethyl carbamate may beformed in the distillation of beers producedwith the use of urea as a yeast nutrient. It doesnot present a significant hazard if such ethanolis only used for fuel purposes, but may presentproblems in the production of whiskies.

Ethylene glycol A slightly viscous, sweet-tasting,poisonous liquid. Chemical formulaCH2OHCH2OH. It has a boiling point of197.6oC, and is considerably hygroscopic. Itis commonly used as an antifreeze. It mayalso be used as an extractant in extractivedistillation processes for the dehydration ofethanol. (See extractive distillation.)

Ethyl tertiary butyl ether (ETBE) A colorless,flammable, oxygenated hydrocarbon .Chemical formula C2H5OC4H9. It may beproduced from ethanol and tertiary butanol

(TBA) or isobutylene. It is of similar structureto methyl tertiary butyl ether (MTBE), havingsimilar octane-enhancing properties, but hasa significantly lower effective Reid vaporpressure in blending with gasoline.

Evaporation The process by which a substancein the liquid state is converted into the vaporstate.

Evaporator A device used to evaporate part orall of a liquid from a solution. In the case ofgrain stillage processing, evaporators may beused to concentrate screened thin stillage to asyrup of about 35% solids, which may thenbe fed to a dryer. Evaporators are normallyoperated under vacuum (to obtain a lowerboiling point of the liquid) and may consist ofa series of interlinked vessels or effect soperating under differing degrees of vacuum.

Excise tax exemption When fermentationethanol is blended at a 10% concentrationwith gasoline, it is effectively exempted fromthe US federal excise tax at the rate of 60 centsper gallon of ethanol used or 6 cents per gallonof blend. This comes from the fact that theethanol itself is exempted from the entire 9cents per gallon of tax, and each of the 9gallons of ethanol required to make a 10%blend is exempted from 5.66 of the 9 centsper gallon tax. This exemption was firstintroduced under the Energy Tax Act of 1978at a rate of 4 cents per gallon (the entirety ofthe tax at that time). It was increased to 5 centsper gallon under the Surface TransportationAssistance Act of 1982 when the excise taxwas raised to 9 cents. It was increased to thecurrent effective level of 6 cents per gallonunder the Deficit Reduction Act of 1984. Itwas scheduled to expire in 1992, but wasextended to September 30, 1993 under theSurface Transportation and Uniform RelocationAssistance Act of 1987.

Extractant A substance such as ethylene glycolor glycerol be used in extractive distillationprocesses for the dehydration of ethanol.

362 J.E. Murtagh

Extractive distillation A process where anextractant is added to a mixture being distilledto change the volatilit y of one or morecomponents. The less volatile mixture will thendescend in a continuous distillation columnwhile the more volatile components may beremoved in the condensed overhead vapors.In the use of extractive distillation in thedehydration of ethanol, liquid extractants suchas ethylene glycol, or glycerol, may be used.Salts such as potassium and sodium acetatesmay also be used alone in molten form or inmixtures with glycerol, etc. Anhydrous ethanolis recovered in the overhead condensate whilethe water combines with the extractant toemerge from the bottom of the column. (Thisis the reverse of the situation in azeotropicdistillation.) The extractant is then separatedfrom the water in another column (or anevaporator) and is recycled.

In the production of neutral spirit, light rumsor whiskies, extractive distillation may be usedto remove fusel oils and some other congenersin the condensed overhead vapors. In thisinstance the extractant is water, as some ofthe congeners with lower volatilit y thanethanol in a concentrated state may havehigher volatility than ethanol when diluted withwater and therefore rise up the extractivedistillation column while the ethanol descends.

Exoenzyme An enzyme restricted to acting onthe outer end of large polymeric moleculesand cleaves molecules one by one. (SeeEndoenzyme.)

F

Facultative anaerobe Term used to describe amicroorganism (such as a yeast) that isessentially aerobic (or air-requiring), but canalso thrive under anaerobic (or air-free)conditions.

Fahrenheit scale A temperature scale in whichthe boiling point of water is 212oF and the

freezing point is 32oF. (The zero point wasoriginally established as the lowest pointobtainable with a mixture of equal weights ofsnow and common salt.)

Farmers Home Administration (FmHA) Adivision of the US Department of Agriculturewhich among other activities is empoweredto make loan guarantees for the establishmentof ethanol production plants.

Federal Excise Tax Exemption See Excise taxexemption.

Feed plate (or feed tray) The plate or tray ontowhich the distilland (liquid to be distilled) isintroduced in a distillation column. In theory,it is the point in a column above whichenrichment or concentration occurs andbelow which stripping occurs.

Feedstock The raw material used in a process.For example, corn, molasses, whey, etc. maybe used as feedstocks for ethanol production.

Fermentable sugars Simple sugars such asglucose and fructose that can be convertedinto ethanol by fermentation with yeast. Theymay be derived by the hydrolysis of starch orcellulose feedstocks or obtained from othersources.

Fermentation The enzymatic transformation bymicroorganisms of organic compounds suchas sugars. It is usually accompanied by theevolution of gas as in the fermentation ofglucose into ethanol and carbon dioxide.

Fermentation efficiency The measure of theactual output of a fermentation product suchas ethanol in relation to the theoretical yield.

Fermentation ethanol The term used todistinguish ethanol produced by fermentationfrom synthetic ethanol produced fromethylene, etc. The difference is significant inthat only fermentation ethanol qualifies for USfederal and state excise tax exemptions forautomotive fuel use. Furthermore, onlyfermentation ethanol may be used forbeverage purposes.

The Alcohol Alphabet 363

Fermenter The vessel in which mashfermentation takes place. The vessel may befabricated from steel, fiber glass, etc. and isnormally fitted with an internal or externalcooling system for controlling temperature ofthe fermenting mash.

FFV Abbreviation for Flexible Fueled Vehicle.

Flame arrester A device installed on the vaporvents of alcohol storage tanks and distillationcolumns to prevent entry of flames that mightcause an explosion. It normally contains finemetal meshes with holes large enough to allowvapors to escape, but too small to allow flamesto pass in the opposite direction.

Flash cooling The rapid cooling achieved whena hot liquid is subjected to a sudden pressuredrop to reduce its boiling point.

Flash point The minimum temperature at whicha combustible liquid will ignite when a flameis introduced. It depends on the volatility ofthe liquid to provide sufficient vapor forcombustion. For example, anhydrous ethanolhas a flash point of 51oF, while 900 proofethanol has a flash point of 78oF.

Flexible fueled vehicle (FFV) A vehicle designedto operate on a variety of fuels such asmethanol, ethanol or gasoline alone or incombinations without requiring majoradjustments.

Flocculation The aggregation or coalescing offine suspended particles or bodies into looseclusters or lumps. The f locculationcharacteristics of yeast or other microorganismsmay be important features in their recoveryfor cell recycling.

Flowmeter A device for measuring the rate offlow of a liquid.

FmHA Abbreviation for the Farmers HomeAdministration.

Fluidized bed combustion boiler A boiler inwhich the coal or other fuel particles are keptin suspension by a rising column of gas ratherthan resting on a conventional grate. Thesystem gives greater heat transfer and higher

potential combustion efficiency. The systemhas the advantage that limestone may beadded to the coal fuel to absorb sulfur gasesto reduce emissions.

Fossil fuel Any naturally-occurring fuel of anorganic nature that originated in a pastgeologic age such as coal, crude oil or naturalgas.

Fractional distillation A process of separatingmixtures such as ethanol and water by boilingand drawing off the condensed vapors fromdifferent levels of the distillation column.

Fructose A fermentable monosaccharide(simplesugar) of the chemical formula C6H12O6. Itschemical structure is similar to that of glucose,but it is sweeter to the taste. It may beproduced from glucose by enzymaticisomerization, as in the production of highfructose corn syrup (HFCS).

Fuel grade ethanol See motor fuel grade ethanol.

Fuel ethanol Usually denotes anhydrous ethanolthat has been denatured by addition of 2-5%unleaded gasoline and is intended for use asan automotive fuel in blends with gasoline.

Fungible Literally means interchangeable intrade. Commonly used to denote productssuitable for transmission by pipeline. Ethanolis not considered fungible in this sensebecause it would absorb any wateraccumulating in pockets in a pipeline.

Fusel oil Term used to describe the higheralcohols, generally the various forms ofpropanol, butanol and amyl alcohol that arecongeners or by-produc t s of ethanolfermentation. Normally, predominantlyisoamyl alcohol. Their presence in alcoholicbeverages is known to be a cause ofheadaches and hangovers. The fusel oils havehigher boiling points than ethanol and aregenerally removed in the distillation processto avoid accumulation in the rectifier. Theymay be subsequently added back into theanhydrous product for motor fuel gradeethanol.

364 J.E. Murtagh

Fusel oil decanter A device used to separateaccumulations of fusel oil from ethanol basedon the fact that fusel oil has a lower miscibilityin water than ethanol and can therefore beremoved by dilution with water. It generallyconsists of a tank with windows or sight glassesto permit the operator to observe and controlthe separation.

G

Galactose A monosaccharide of chemicalformula C6H12O6 that along with glucose is aconstituent of the disaccharide lactose. It isan isomer of glucose, but is less-readilyfermented by yeasts to ethanol.

Gas chromatography (GC) A technique forseparating chemical substances in which thesample is carried by an inert gas streamthrough a tube (or column) packed with afinely-divided solid material. The variouscomponents in the sample pass through thecolumn at differing velocities and emerge fromthe column at distinct intervals to be measuredby devices such as a flame ionization detectoror a thermal conductivity detector. (Wherethe solid material in the column is pretreatedwith a liquid to achieve the componentseparation, the process may be referred to asgas liquid chromatography) The techniquemay be used for separating and measuring theamount of ethanol and the various by-productsformed in fermentation.

Gas liquid chromatography See gaschromatography.

Gasohol (or gasahol) A trade name registeredby the Nebraska Agricultural ProductsIndustrial Utilization Committee, later renamedthe Nebraska Gasohol Committee. (Thecommittee was responsible for laying thegroundwork for the development of thepresent day US fuel ethanol industry). Thetrade name, in either spelling, covers a blendof anhydrous ethanol derived from

agricultural products with gasoline (notnecessarily unleaded). The committee hasfreely granted permission for commercial useof the trade name provided it is not used forblends containing alcohols other than ethanol.

Gasoline A volatile, f lammable, l iquidhydrocarbon mixture suitable for use as a fuelin internal combustion engines. Normallyconsists of a blend of several products fromnatural gas and petroleum refining togetherwith anti-knock agents and other additives. Itis a complex mixture of hundreds of differenthydrocarbons, generally in the range of 4-12carbon atoms per molecule. The componentsmay have boiling point s ranging mainlybetween 30 and 200oC with blends beingadjusted to altitude, season and legalrequirements.

Gasoline extender The term used to describeethanol when it is simply used as a partialreplacement for gasoline without anyconsideration for its value as an octaneenhancer or oxygenate.

Gay Lussac (GL) The name given to a scale ofthe concentration of ethanol in mixtures withwater where each degree is equal to 1% byvolume (i.e., 1o GL is equivalent to 2o USproof). It takes the name from the Frenchchemistry pioneer, Joseph-Louis Gay Lussac.

Gay Lussac equation The equation for thefermentation of sugar by yeast to carbondioxide and ethanol, established by the Frenchchemist Joseph-Louis Gay Lussac in 1815:C6H12O6 2CO2 + 2C2H5OH. (SeeStoichiometric yield).

GC Abbreviation for gas chromatograph.

Gear pump A positive displacement rotary pumpcontaining two intermeshed gear wheels in asuitable casing. The counter rotation of thegears draws fluid between the gear teeth onone side and discharges it on the other side.It is commonly used for viscous liquids suchas molasses and stillage syrup.

Gelatinization In reference to the cooking ofstarchy feedstocks, gelatinization is the stage

The Alcohol Alphabet 365

in which the starch granules absorb water andlose their individual crystalline structure tobecome a viscous liquid gel. Gelatinization issignificant in that it is the preliminary processnecessary to render starch susceptible toenzymatic hydrolysis for conversion tofermentable sugars.

Gin Defined by the BATF as a product obtainedby original distillation from mash, or byredistillation of distilled spirits, or by mixingneutral spirits with or over juniper berries andother aromatics, or with or over other extractsderived from infusions, percolations ormaceration of such materials, and includesmixtures of gin and neutral spirits. It shallderive its main characteristic flavor fromjuniper berries and be bottled at not less than800 proof. Gin produced exclusively byoriginal distillation or redistillation may befurther designated as distilled.

GL Abbreviation for Gay Lussac.

GLC Abbreviation for gas-liquid chromatography.

Glucoamylase. An enzyme that hydrolyses starchinto its constituent glucose units. (SeeAmyloglucosidase.)

Glucan. See Betaglucan.

Glucanase An enzyme that hydrolyses glucan.(See Betaglucanase.)

Glucose A fermentable sugar otherwise referredto as dextrose. It is a monosaccharide and hasthe formula C6H12O6. Glucose is the ultimateproduct in the hydrolysis of starch andcellulose, which are both polymers of hundredsor thousands of glucose units.

Glucose isomerase An enzyme that convertsglucose into its isomer, fructose. It is used inthe production of high fructose corn syrup(HFCS).

Glucosidase See Amyloglucosidase orGlucoamylase.

Glycerol (or glycerine) A clear, colorless,viscous, sweet-tasting liquid belonging to thealcohol family of organic compounds. It has a

chemical formula of CH2OHCHOHCH2OH,having three hydroxyl (OH) groups. It is a by-product of alcoholic fermentations of sugars.It is hygroscopic and may be used as anextractant in the dehydration of ethanol.

Grain alcohol Term used to distinguish ethanolproduced from grain from ethanol producedfrom other feedstocks, or from wood alcohol(methanol).

Grain whisky The term used in Scotland todistinguish the bland, nearly-neutral,continuous distillation product that forms thebase of blended Scotch whisky from the maltwhiskies that contribute most of the flavor inthe blend. Grain whisky is usually producedfrom corn or barley.

Grain sorghum Otherwise known as milo, asorghum grown for grain production, asdistinct from sweet sorghum grown for thesugar content of its stem. It may be used as afeedstock for ethanol production.

Gram-negative See Gram stain.

Gram-positive See Gram stain.

Gram stain A widely-used microbiologicalstaining technique that aids in the identificationand characterization of bacteria. It wasdevised by Danish physician, Hans ChristianGram. Bacteria are described as Gram-positiveif their cell walls absorb the stain and Gram-negative if they do not. The technique isparticularly useful in examining bacterialcontaminants in fermentations, as most Gram-positives are susceptible to control bypenicillin.

H

Hammer mill A type of impact mill or crusherin which materials such as cereal grains arereduced in size by hammers revolving rapidlyin a vertical plane within a steel casing. Ascreen with numerous holes of a selected

366 J.E. Murtagh

diameter is installed in the casing to controlthe size of particles produced. It is commonlyused for grinding corn as a fermentationfeedstock.

Heads Term used to describe the impuritiesproduced in ethanol fermentations (congeners)that have lower boiling points than ethanol.They include methanol and aldehydes.

Heads concentrating column A distillationcolumn used to concentrate heads removedin the production of neutral spirit, light rumsand whiskies.

Heat exchanger Device used to transfer heatfrom a fluid on one side of a barrier to anotherfluid flowing on the other side of the barrier.Common forms include shell-and-tube heatexchangers and plate-type heat exchangers.Various types of heat exchangers are used inethanol plants for mash cooling, indirect steamheating (reboilers), overhead vaporcondensing, etc.

Heat of condensation The heat given up whena vapor condenses to a liquid at its boilingpoint.

Heat of vaporization The heat input requiredto change a liquid at its boiling point to a vaporat the same temperature.

Hemicellulose Term used to describe non-cellulosic polysaccharide components of plantcell walls. The most common hemicellulosesare composed of polymers of xylose (a 5-carbon sugar, or pentose) together with auronic acid (a sugar acid), arabinose (anotherpentose) and mannose (a hexose).Hemicelluloses have no chemical relationshipto cellulose. They frequently surround thecellulose fibers and increase their bonding andtensile strength. The presence ofhemicelluloses (and l ignins) in closeassociation with cellulose tends to impede theextraction and hydrolysis of wood cellulose tosugars for ethanol production.

Hexose A class of monosaccharides (simplesugars) containing six carbon atoms in the

molecule. They have the formula C6H12O6.Common examples are glucose, fructose andgalactose.

HFCS Abbreviation for high fructose corn syrup.

Hiag process A process developed in Germanyin the 1930s for the dehydration of ethanol byextractive distillation using a mixture of sodiumand potassium acetates as the extractant.

High boilers Term used to describe theimpurities produced in ethanol fermentation(congeners) that have higher boiling pointsthan ethanol. Otherwise referred to as tails,they include the higher alcohols, propanols,butanols and amyl alcohols or fusel oils. Inthe context of gasoline, the term refers tocomponents with boiling points considerablyabove the mid-range.

Higher alcohols Alcohols having more than twocarbon atoms. They exist in various isomericforms. As the number of carbon atomsincreases, so does the number of isomers, butat a greater rate. The lower members of thisgroup, namely propanol, butanol and amylalcohol are major constituents of fusel oil.

High fructose corn syrup (HFCS) A product inwhich a large percentage of the glucosederived from starch hydrolysis has beenconverted into its sweeter-tasting isomerfructose by use of enzymes. It is frequentlyused as a substitute for cane or beet sugar asa sweetener in soft drinks, etc. It is a seasonalalternative to ethanol production in some cornprocessing plants.

High performance liquid chromatography(HPLC) An advanced form of liquidchromatography used for the separation ofcomplex mixtures of non-volatile materials foranalytical purposes. It involves very smallparticles packed in columns through which theliquids flow and high pressures to increase therate of flow and shorten the time required toachieve the separation. The process iscoupled with other devices to identify theconstituents. It may be used in the analysis of

The Alcohol Alphabet 367

the sugars and dextrins produced by hydrolysisof starch.

High test molasses (HTM) See molasses.

Hogshead A wooden barrel with a capacity ofapproximately 66 US gallons (250 liters) usedin Scotland for aging whisky. It is usuallyconstructed from shooked bourbon whiskeybarrels of 52 gallons capacity by usingadditional staves and larger heads and hoops.

HPLC Abbreviation for high performance liquidchromatography.

HTM Abbreviation for high test molasses.

Hydrocarbon A member of a class of organicchemical compounds containing onlyhydrogen and carbon. It should be clearlydifferentiated from carbohydrates, whichcontain oxygen as well as hydrogen andcarbon. The main natural sources ofhydrocarbons are petroleum, coal, natural gasand bitumens.

Hydrolysis Literally means the breakdown,destruction or alteration of a chemicalsubstance by water. In the case of starch andother polymers of glucose, a molecule of wateris divided between two adjacent glucose units,in order to cleave the linkage. For example,maltose (C12H22O11), which contains twoglucose rings, requires the addition of amolecule of water (H2O) to yield two separateglucose molecules (C6H12O6). The hydrolysismay be accomplished with the use of acids orenzymes.

Hydrometer An instrument measuring thedensit y, specific gravit y or other similarcharacteristics of liquids. It is generallycomprised of a long-stemmed glass tube witha weighted bottom which floats at differentlevels in liquids of different densities. Thereading is taken at the meniscus (where thecalibrated stem emerges from the liquid). Theliquid temperature is normally determinedwhen taking a reading; and reference is madeto hydrometer tables to obtain a correctionto a standard temperature. A proof hydrometer

measures the content of ethanol in a mixturewith water. A Brix or Balling hydrometermeasures on a scale equivalent to thepercentage of sugar by weight in an aqueoussolution.

Hydroselection column Synonym for extractivedistillation column.

Hydrous ethanol Term used for ethanol that hasnot been subjected to dehydration. It may referto any mixture of ethanol and water, butfrequently is used to denote ethanol at aconcentration of about 190-1920 proof, closeto the azeotropic point.

Hygroscopic Term used to describe a substancewith the property of absorbing moisture fromthe air. Anhydrous ethanol is hygroscopic, andits exposure to moist air should therefore beminimized.

Hydroxyl group A combination of one atom ofoxygen and one atom of hydrogen (OH)forming an essential part of any alcohol. Thespare atomic bond of the group is linked to acarbon atom as in ethanol (C2H5OH) ormethanol (CH3OH).

I

IDRB Abbreviation for Industrial DevelopmentRevenue Bonds.

Imperial gallon A measure of volume in theBritish system defined in 1824 as the volumeoccupied by 10 pounds of water at 62oF and30 inches of barometric pressure. It is theequivalent of 1.2 US gallons, or 4.546 liters.

Industrial alcohol Denotes any ethanol intendedfor industrial uses such as solvents, extractants,antifreezes and intermediates in the synthesisof innumerable organic chemicals. The termcovers ethanol of both synthetic andfermentation origin of a wide range of qualitiesand proofs, with or without denaturants.

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Industrial development revenue bonds (IDRB)Debt incurred through local industrialdevelopment authorities in numerous USstates. Such bonds were a popular way tofinance fuel ethanol plants in the past becausethe interest on the bonds was not subject toincome tax and the bonds could be sold withinterest rates substantially below the prime rate.

Inoculum The portion of a culture of yeast (orbacteria) used to start a new culture or afermentation.

Inulin A storage polysaccharide found in theroots and tubers of various plants, particularlyJerusalem artichokes. It consists of chains ofan average of 30 fructose units. It is only slightlysoluble in cold water, but dissolves readily inhot water. Unlike starch, it does not give a colorreaction with iodine.

Inulinase An enzyme capable of hydrolyzinginulin to its component fructose units.

IPE Abbreviation for isopropyl ether.

Isoamyl alcohol The principal alcohol in fuseloil. It is an isomer of pentanol, of compositionC5H11OH. It is a colorless liquid with a pungenttaste and disagreeable odor. Boils at 132oCand freezes at -117.2oC. It is only slightlysoluble in water but miscible with ethanol. Itmay be recovered by fractionation of fusel oil,and has a wide range of uses in organicsynthesis, pharmaceuticals, photographicchemicals and as a solvent for fats, etc. Thevapors are poisonous and at lowconcentrations may cause headaches anddizziness.

Isomer One of a series of two or more moleculeswith the same number and kind of atoms andhence the same molecular weight, but differingin respect to the arrangement or configurationof the atoms. For instance, glucose and fructosehave the formula C6H12O6, but differentmolecular structures.

Isomerase An enzyme that can convert acompound into an isomeric form. For instance,the glucose isomerase enzyme converts

glucose into its sweeter-tasting isomer fructosein the production of high fructose corn syrup(HFCS).

Isomerization The process of converting achemical compound into its isomer such asconverting glucose to fruc tose in theproduction of high fructose corn syrup (HFCS).In petroleum refining, the term describesmethods used to convert straight-chain tobranched-chain hydrocarbons, or acyclic toaromatic hydrocarbons to increase theirsuitability for high octane gasoline.

Isopropyl ether (IPE) An ether (otherwiseknown as di-isopropyl ether) used in some fuelethanol plants as an entrainer in thedehydration process as an alternative tobenzene, etc. It is a colorless, volatile liquidwith chemical formula (CH3)2CHOCH(CH3)2,which boils at 67.5oC and freezes at -60oC. Itreadily forms explosive mixtures with air.Inhalation of vapors may cause narcosis andunconsciousness.

J

Jet cooker An apparatus for the continuouscooking of grain mashes in which the mash ispumped past a jet of steam that instantly heatsthe mash to gelatinize the starch.

Jobber A gasoline wholesaler. Some jobbers mayoperate under contract to one or more majoroil companies, distributing gasoline to brandedgas stations. Other jobbers may operateindependently, buying gasoline from varioussources for distribution to unbranded retailoutlets. Independent jobbers are frequentlymajor buyers and blenders of fuel ethanol.

K

Karl Fischer titration A method to chemicallydetermine the amount of water present in a

The Alcohol Alphabet 369

sample of ethanol and/or other substances.When correctly practiced, the methodprovides an extremely accurate measurementof very small quantities of water in ethanoleven if gasoline denaturant is present. (Seetitration).

Kerosene One of the three permissibledenaturants for fuel ethanol as specified inBATF regulations. It is a refined petroleumfraction used as a fuel for heating, cookingand for jet engines. It has a boiling point rangesomewhat higher than that of gasoline,generally between 180oC and 290oC.

Kjeldahl method An analytical method for thedetermination of nitrogen in organiccompounds. As nitrogen is an essentialelement in protein, the method may be usedfor determining protein in such materials asdistillers dried grains. Kjeldahl protein, or crudeprotein, is Kjeldahl N x 6.25.

Kluyveromyces fragilis (or marxianus) A lactose-fermenting yeast used in the production ofethanol from cheese whey.

Kubierschky process The first patented processfor the continuous dehydration of ethanol withbenzene. With relatively minor variations, theprocess developed in 1914 based on Youngsearlier batch process is still used today in manyfuel ethanol plants.

L

Lactase An enzyme that hydrolyzes lactose intoglucose and galactose. This hydrolysis allowslactose-containing feedstocks such as cheesewhey to be fermented by the commonSaccharomyces cerevisiae yeasts. A principalsource of lactase is the yeast Kluyveromycesfragilis, which can also directly ferment lactoseto ethanol.

Lactic acid The organic acid produced in thefermentation of carbohydrates by Lacto-bacillus bacteria. Its production is the principal

reason for loss of yield in contaminatedethanol fermentations. Pure lactic acid is acolorless, odorless, hygroscopic, syrupy liquidwith a boiling point of 122oC and a formulaCH3CHOHCOOH.

Lactobacillus A genus of bacteria that producelac tic acid as a major product in thefermentation of carbohydrates. Lactobacilli arefound extensively in fermenting food productssuch as souring milk and in grain dust. Theyare the principal cause of loss of yield inethanol fermentations. Otherwise referred toas lactic acid bacteria, they are generally Gram-positive and controllable with penicillin andcertain other antibiotics.

Lactose The principal sugar in milk and cheesewhey. It may be fermented by suitable yeaststo ethanol. It is a disaccharide readilyhydrolysed to its two components, glucose andgalactose. Lactose has the formula C12H22O11.

Lag phase Applied to yeast propagation, lagphase refers to the initial period in which theyeast inoculum becomes adapted to the mashprior to the rapid increase in cell numbersreferred to as the logarithmic phase.

Latent heat The quantity of energy absorbed orreleased when a substance undergoes achange of state, i.e., from a solid to a liquid(melting) or from a liquid to a vapor, or viceversa. No change in temperature is involved.For example, water requires a large amountof latent heat (measured in BTUs or calories)to convert from the liquid to vapor state(steam) at 100oC, while steam releases thelatent heat again on condensing back to theliquid state.

Lead phase-out The reduction in the amount oflead (normally in the form of tetraethyl lead)that could be used as an octane enhancer inleaded gasoline in the US. The reduction,which went from 1.1 grams per gallon priorto July 1, 1985 to less than 0.1 grams per gallonafter January 1, 1986 caused an increase indemand for alternative octane enhancers suchas ethanol and MTBE.

370 J.E. Murtagh

Light whisky Defined by the BATF as whiskyproduced at more than 1600 proof and storedin used or uncharred oak barrels.

Lignin A polymeric , non-carbohydrateconstituent of wood that functions as asupport and plastic binder for cellulose fibers.It may comprise 15-30% of wood and can onlybe separated from the cellulose andhemicellulose components by chemicalreaction at high temperatures. Its presence inwood is a major barrier to the hydrolysis ofcellulose to sugars for fermentation purposes.

Lignocellulose Woody materials made up largelyof lignin, cellulose and hemicelluloses. Thechemical bonding between the constituentsrenders it resistant to hydrolysis.

Lime A white alkaline powder composed ofcalcium oxide. It is added to grain mash toadjust the pH and to provide calcium ions inorder to prevent the inactivation of the "-amylase enzyme molecule by the loss of itsessential calcium atom.

Liquefaction Conversion of a solid substanceto the liquid state. In reference to starch, it isthe stage in the cooking and saccharificationprocess in which gelatinized starch is partiallyhydrolyzed by "-amylase (or occasionally byan acid) to give soluble dextrins. This convertsthe starch mash into a free-flowing liquid.

Liqueurs and cordials Defined by the BATF asproducts obtained by mixing or redistillingdistilled spirits with or over fruits, flowers, plantsor pure juices therefrom, or any other naturalflavoring materials, or with extracts derivedfrom infusions, percolation or maceration ofsuch materials, and containing sugar, dextroseor levulose, or a combination thereof, in anamount not less than 2.5% by weight of thefinished product.

Liter A metric measurement of volume definedas the equivalent of 1000 cubic centimetersor 0.2642 US gallons.

Loan guarantee A procedure by which the DOEand FmHA separately encouraged the

construction of fuel ethanol plants by actingas guarantors for up to 90% of the amount ofloans made by banks and other lenders toapproved borrowers.

Logarithmic phase Applied to yeastpropagation, it refers to the period in whichcell numbers increase at an exponential rateafter the initial lag phase.

Low boilers In reference to ethanol distillation,the term is applied to the congeners, orfermentation by-products, which boil at a lowertemperature than ethanol. More commonlyreferred to as heads, these compounds areprincipally aldehydes and methanol.

LPA Abbreviation for liters of pure alcohol.

M

Macromolecule A giant molecule in which thereis a large number of one or more relativelysimple structural units or monomers.

Malt Barley grains that have been steeped inwater and then allowed to germinate. Thegermination is normally halted by drying thegrains when the sprouts are about the samelength as the grains. At this stage, the malt (ormalted barley) contains considerableamounts of "- and -amylase enzymes thatsaccharif y the barley starch and otheradditional starch in a mash to yield fermentablesugars. (In Scotland, the drying may be doneby exposing the malt to a flow of peat smoketo impart a smoky odor to the malt.) Malt isused in whisky production, mainly for itscontribution to product flavor. In fuel ethanolproduction the necessary saccharif yingenzymes are normally derived from microbialsources.

Malt whisky In the US malt whisky is definedby the BATF as a whisky produced at less than1600 proof from a fermented mash containingat least 51% malted barley, and stored at under

The Alcohol Alphabet 371

1250 proof in charred, new oak barrels. InScotland, malt whiskies are made from a 100%malted barley mash and may be aged inpreviously-used oak barrels. Malt whiskies maybe mixed with grain whiskies to impart muchof the characteristic flavor of blended Scotchwhisky.

Maltase An enzyme capable of hydrolyzingmaltose sugar molecules into their twocomponent glucose units. Occasionally thename is loosely applied to theamyloglucosidase enzyme, which hydrolyzespolysaccharides to glucose.

Maltose A fermentable sugar which is a dimer(or disaccharide) of glucose in that it iscomprised of two linked glucose units. It isthe normal end product of starchsaccharification by the -amylase enzyme inmalt.

Manioc See cassava.

Mannose A fermentable 6-carbon sugar (orhexose) which is an isomer of glucose.Chemical formula C6H12O6. It is a constituentof hemicellulose.

Mash A mixture of milled grain or otherfermentable carbohydrate in water used in theproduction of ethanol. The term may be usedat any stage from the initial mixing of thefeedstock in water prior to any cooking andsaccharification through to the completion offermentation, when it becomes referred to asbeer.

Mash bill The percentages of different types ofgrains used in the preparation of a mash inbeverage alcohol production. For example, atypical bourbon whisky mash bill may consistof 65% corn, 25% rye and 10% barley malt.

McCabe-Thiele diagram A graphic method forcalculation of the number of theoretical plates(or trays) required in a distillation column toachieve a desired separation of twocomponents.

Meal The floury or granular product resultingfrom milling or grinding of cereal grains.

Mechanical vapor recompression (MVR) Amethod used in evaporation in which the watervapor leaving the evaporator is recompressedand recycled to heat the same vessel. Thismeans that mechanical energy is used ratherthan heat energy. The recompressor may beoperated by electricity or by a steam turbine(if high pressure steam is available and thereis a demand elsewhere for the low pressureturbine exhaust steam). Mechanical vaporrecompression can greatly increase the steamusage efficiency, but the capital costs forequipment are also greater.

Metabolism The chemical processes in livingcells by which energy is derived for vitalprocesses, growth and activities.

Methane A colorless, odorless, tasteless, readily-combustible, asphyxiant, lighter-than-air gas.The first member of the paraffin (or alkane)series of hydrocarbons, it has a formula CH4.It occurs in high proportions in natural gas,and is produced by decaying vegetation andother organic matter as in landfills and marshes.The methane produced in sealed landfills orfrom the anaerobic digestion of thin stillageand other wastewaters is used for boiler fuelin some ethanol plants.

Methane digester (or anaerobic digester) Asystem of covered tanks used for treatment oforganic waste streams such as thin stillage. Thesystem is initially inoculated with a suitableculture of methane-producing bacteria andoperates on a continuous basis to generatemethane for use as a boiler fuel.

Methanol (or methyl alcohol) A colorlesspoisonous liquid with essentially no odor andvery little taste. It is the simplest alcohol andhas the formula CH3OH. It boils at 64.7

oC. Itis miscible with water and most organic liquids,including gasoline. It is extremely flammable,burning with a nearly invisible blue flame. It isa congener of ethanol fermentations. Havinga lower boiling point than ethanol, it tends tobe a major component of the heads streamon distillation. Due to its miscibility with

372 J.E. Murtagh

benzene, its presence in a hydrous ethanolfeed may reduce the efficiency of dehydrationprocesses where benzene is used as anentrainer. Methanol is produced commerciallyby the catalyzed reaction of hydrogen andcarbon monoxide. It was formerly derivedfrom the destructive distillation of wood, whichcaused it to be known as wood alcohol.Methanol may be blended with gasoli