Wheat Chemistry & Technology

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Unit 1: Production, quality and milling

Production and Utilization Classification, Structure and Composition Drying, Grading and Storage Criteria of Wheat Grain Quality

Physical Criteria Chemical Criteria

Wheat Milling• Aims of Milling

• General Process

• Milling Machinery2

Production of Wheat in the World

• Production (600-650 million tonnes per annum).

• India is the 2nd largest wheat producing country next to China.

• Wheat is a main staple food as 65 % of produced are directly used as food for humans, 21% as a live stock feed , 8% as seed material, and remaining 6% as industrial raw material.

• 95% wheat is Triticum aestivum (hexaploid type); 5% are durum (tetraploid).

• Normal world productivity is 2.8 tonnes/hectare.

• Major Wheat producers (75% of world production ): China, India, USA, Russia, Canada, Australia, France, Iran, Pakistan, Turkey, UK, Argentina, and Italy. 3

CountryCountry Area (%)Area (%) CountryCountry Production (%)Production (%)

ChinaChina 13.1913.19 ChinaChina 18.4118.41

IndiaIndia 12.512.5 IndiaIndia 12.0512.05

USAUSA 10.3810.38 USAUSA 10.9710.97

Russian Fed.Russian Fed. 9.219.21 FranceFrance 6.526.52

AustraliaAustralia 5.565.56 Russian Fed.Russian Fed. 5.365.36

CanadaCanada 4.954.95 CanadaCanada 4.434.43

TurkeyTurkey 4.134.13 AustraliaAustralia 3.763.76

PakistanPakistan 3.873.87 PakistanPakistan 3.293.29

ArgentinaArgentina 2.712.71 TurkeyTurkey 3.083.08

IranIran 2.542.54 United KingdomUnited Kingdom 2.682.68

FranceFrance 2.422.42 ArgentinaArgentina 2.512.51

ItalyItaly 1.081.08 IranIran 1.571.57

SpainSpain 1.041.04 ItalyItaly 1.341.34

United KingdomUnited Kingdom 0.920.92 EgyptEgypt 1.081.08

RomaniaRomania 0.870.87 SpainSpain 1.021.02

SyriaSyria 0.780.78 RomaniaRomania 0.810.81

EgyptEgypt 0.470.47 SyriaSyria 0.560.56

BangladeshBangladesh 0.390.39 BangladeshBangladesh 0.320.32

Others Others 23.0023.00 Others Others 20.2420.24

Share of countries in terms of area and production of wheat worldwide

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Wheat is grown over an area of about 28 million hectares with annual production of about 72-82 million tonnes.

Normal National productivity is about 2.8 tonnes/hectare.

Major wheat producing States (99% production): Uttar Pradesh, Punjab, Haryana, Madhya Pradesh, Rajasthan, Bihar, Maharashtra, Gujarat, Karnataka, West Bengal, Uttaranchal, Himachal Pradesh and Jammu & Kashmir.

Wheat in India stands next to rice, both in area and production.

Wheat production in India

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StateState Area (%)Area (%) StateState Production (%)Production (%)

Uttar PradeshUttar Pradesh 33.833.8 Uttar PradeshUttar Pradesh 33.733.7

Madhya PradeshMadhya Pradesh 14.814.8 PunjabPunjab 21.221.2

PunjabPunjab 12.712.7 HaryanaHaryana 12.912.9

RajasthanRajasthan 9.79.7 Madhya PradeshMadhya Pradesh 9.69.6

HaryanaHaryana 8.78.7 RajasthanRajasthan 8.98.9

BiharBihar 7.87.8 BiharBihar 6.26.2

MaharashtraMaharashtra 3.53.5 MaharashtraMaharashtra 1.71.7

GujaratGujarat 1.81.8 GujaratGujarat 1.61.6

UttaranchalUttaranchal 1.51.5 West BengalWest Bengal 1.21.2

West BengalWest Bengal 1.51.5 UttaranchalUttaranchal 1.01.0

Himachal PradeshHimachal Pradesh 1.41.4 Himachal PradeshHimachal Pradesh 0.80.8

OthersOthers 2.82.8 OthersOthers 1.21.2

Share of States in terms of area & wheat production

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UTILIZATION Of WHEAT

• Wheat is the staple food due to its relatively easy harvesting, storing, transportation and processing.

• Only wheat flour (to limited extent rye flour) has ability to form dough that retains gases &produces a baked product.

• Various wheat products : breads, cakes, noodles, crackers, breakfast foods, biscuits, cookies, chapatti, macaroni, spaghetti, pizzas, doughnuts, confectionary items, semolina , rava or sooji, Vermicelli etc. 7

Classification of wheat

i. Bread Wheat (Triticum aestivum): hexaploid  species

ii. Club Wheat (Triticum Compactum): kernels have a soft texture and low protein content (cake, pastry).

iii. Durum Wheat (Triticum durum): tetraploid wheat (pasta, semolina).

iv. Einkorn Wheat (Triticum monococcum):diploid species

v. Spelt Wheat (Triticum spelta): hexaploid species

Five major categories (differ in quality characteristics that reflected in uses of their milled products).

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Wheat StructureThree major parts of wheat kernel:

i.Endosperm:

•80-85% of kernel weight;

•Source of flour;

•Rich in carbohydrate , protein, iron , B-vitamins and fiber.

ii. Bran:

•15% of kernel weight

•Outer coat of kernel; composed of pericarp, epidermis, hypodermis, tube cells, seed coat testa, and hyaline layer .

•Contains protein, fibers, B vitamins, minerals, antioxidants and phytochemicals

iii. Germ:

•2-3% of kernel weight:

•Consists of plumule, scutellum, radical, root sheath and root cap.

• Rich source of B vitamins, oil, vitamin E. 9

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Composition of wheat

• Mature wheat grain composed of carbohydrates, fat, protein, fiber, minerals and water.

• Starch is found mainly in endosperm

• Crude fiber is found in bran.

• Protein is distributed throughout the grain.

• About half of the total lipids are in endosperm, one fifth in germ and the rest in bran.

• Aleurone is rich in minerals. More than half of the total minerals of wheat grain are present in pericarp, testa and aleurone.

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Component

Whole wheat

Endosperm Germ Aleurone layer

Bran

Protein, %

8.0-16.0

6.0-16.0 24.0-30.0

18.0-24.0 2.8-7.6

Ash, % 1.8 0.5-0.8 3.5-9.5 11.0-17.0 1.7-5.0

Fibre, % 9.0 1.5 8.5 43.0 17.0-73.0

Lipids, %

2.2 1.6-2.0 5.0-18.5

6.0-9.9 0.0-1.0

Starch, %

59.2 63.4-72.5 0.0 0.0 0.0

Chemical composition of wheat

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Drying of wheat Dry, sound wheat can be kept for years if properly

stored.

At harvesting time, grain contains 8-20% moisture.

Grains are dried to 12-13% moisture content for long storage.

In dry areas, wheat contains 8-9% moisture. Water can be added to raise it to 12-13% (desirable level)

Three different systems to dry wheat:

i. natural-air drying binii. low-temperature dryers (less than 40°C) iii. high-temperature or high-speed dryers (temp.

greater than 40°C) 13

Drying of wheat

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Storage• Moisture & temp. are main factors that influence grain quality

grains during storage.• Insect growth & spoilage related to moisture and temp. of stored

wheat.• Proper storage needed to avoid grain damage from insects,

moisture or other adverse storage conditions. :– Plant inspection, good housekeeping, fumigation– Heat treatment of the facility can control infestation – Killing all kinds of insects in bins prior to storage of grains in

bins.• Temp. of 50-55° C in all parts of mill for 10-12 hrs is sufficient to

destroy all insect.

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Grading• Objectives of a grading is to ensure uniform quality so

that products can be priced to satisfy the interests of both the producer and the consumer.

• Wheat grading factors : kernel weight, damaged kernels, shrunken & broken kernels, foreign materials and other seeds

Max. permissible limits of diff. grading factors for wheat

Foreign matter (%)

Other grains

(%)

Damaged grains

(%)

Shriveled and broken grains (%)

0.75 2.0 2.0 7.016

CRITERIA OF WHEAT GRAIN QUALITY

Wheat varieties vary in their morphological, physical and chemical characteristics.

B. Chemical Criteria

i. Moisture content

ii. Protein Content

iii. Protein quality

iv. Alpha-Amylase Activity

v. Ash Content

A. Physical Criteria

i. Test Weight (Weight per Unit Volume)

ii. Thousand Kernel Weight

iii. Kernel Size and Shape

iv. Kernel Hardness

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• Most widely used and simplest criteria of wheat quality. • Determines plumpness of grain.• A rough measure of density of grain in terms of weight per

unit volume.• Expressed in kilogram per hectoliter. kg/hL (100 L).

Test Weight (Weight per Unit Volume)

• Predicts milling quality and is a function of kernel size/density.

• Large & dense wheat kernels have a higher ratio of endosperm to non-endosperm components than smaller & less dense kernels.

• Wheat varieties giving higher kernel wt. give higher flour yield.

• Electronic counter is used for measuring and Expressed in gms/1,000 kernels

• Kernel wt: bread wheat :30-45 gms; durum wheat 35-55 gms.

Thousand Kernel Weight

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Kernel Size and Shape• Variation in wheat depends on internal and external factors

(associated with growth and maturing stages).

• Kernel size related to kernel weight and effect flour yield.

• Size distribution of kernels can be determined using a stack of sieves.

• Based on kernel wt. Wheat grain may be : small (< 32.0g), medium (32.0-38.0g) and bold (>38.0g),

• Based on shape wheat grain may be round, ovate, oblong and elliptical.

• Shape of grain has great influence on milling quality of grain.

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Kernel Hardness Based on hardness, Wheat grain is classified : hard & soft.

Kernel hardness is related to disintegration of endosperm during its separation from bran and germ.

Hard grains yields more flour.

Most part of aleurone layer in soft wheat remains attached with endosperm

Hardness relates to milling performance of wheat.

Flour particles from soft wheat is fluffy; smaller size.

Flow characteristic of soft wheat flour is poor.

Hard wheat requires more grinding force and thus produces flour with high starch damage suitable for bread making.

Hardness can be measured by grinding resistance, particle size index, NIR, penetrometer testing, SKCS,

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Moisture Content

• Most important parameter in judging wheat quality.

• Inversely related to amount of dry matter in wheat.

• Effect keeping quality of wheat.

• Dry, sound wheat can be kept for years ; wet wheat may deteriorate dramatically within a few days.

• At the time of harvest, moisture content of grain is 8-13% depending upon climatic conditions.

• Moisture content can be measured by air oven method, Karl Fischer method, electric moisture meter method etc

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Protein Content Protein content ranges from 6% to 18% depending upon

variety, class and environmental conditions during growth.

Flour should have at least 10% protein for production of yeast leavened bread. (wheat must contain at least 11% protein) .

Wheat grain with 8-10% protein is suitable for biscuits flour productions.

Cookies require a softer type of flour, which provides for structure building and leavening.

Quantity of gluten in flour influences flour strength.

Determination of protein content: Kjeldahl, NIR, etc.22

Protein requirement of different wheat products

Wheat protein content (%)

Type of wheat

End product

13.0 and above Durum Macaroni products

11.5-13.0 Hard Pan bread

10.0-11.0 Hard Crackers

8.0-10.0 Soft Biscuits, pies and cookies

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Protein Quality

Quality of protein plays significant role in the functionality of the wheat flour

Protein quality can be determined by a qualitative estimation of gluten.

Different types of chemical tests: SDS sedimentation volume, baking test of gluten, etc.

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Alpha-Amylase Activity• Diastatic or amylolytic activity is very important quality of flour.

• Diastatic enzymes comprise α-amylase and β-amylase.

• Normally Indian wheat flours contain sufficient amount of β -amylase but lack in α -amylase.

• Sprouting of wheat increases α-amylase in flour.

• α -amylase exerts a major effect on both dough properties & final bread characteristics.

• Flour supplementation with α-amylase results in a bread with improved crust color, finer texture and increased volume.

• Excessive malting decrease water absorption, impart stickiness to dough, cause slackening of dough, reduce loaf volume and produce inferior grain and texture in baked product.

• Can be determined by Amylograph, falling no test. Etc. 25

Ash Content• 1.4 to 2.0 % ash in wheat on 14% moisture basis.

• Ash content reflects quantity of mineral matter present in flour.

• Bran & aleurone layer have higher ash content than endosperm.

• Higher bran contamination in flour indicates higher ash content.

• Small or shriveled kernels have more bran percentage.

• Milled products having higher ash content, are darker in colour.

• Ash test is of greater importance in milling trade than any other test for control of milling operations.

• Factors influencing flour ash: environmental factors, genetic make up of wheat variety and milling conditions such as tempering and grinding. 26

WHEAT MILLINGAims of Milling :

• to separate bran & germ of wheat kernel from endosperm

• to grind separated endosperm into suitable particle size of flour.

• ‘Extraction rate’ refers to flour yield from a given quantity of wheat.

• An extraction rate of 100% indicates 100% of wheat grain is delivered as flour (whole-wheat meal).

• Commercial grade flour has 70% extraction rate, is known as straight-grade flour.

• Efficiency of milling process depends upon type of wheat, milling equipments and skill and experience of miller.

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Milling Process• Steps: receiving of wheat, cleaning, blending, storage,

tempering/conditioning, breaking, sieving, purification and reduction.

• Tempering: process of adjustment of moisture level (15-17%) of wheat grains before milling.

• Milling system consists of break rolls and reduction rolls .

• Break rolls open wheat grains from its crease and scrape endosperm.

• Reduction rolls grind large endosperm particles into flour.

• Roll’s diameters ranges from 180 to 350mm and length upto 1.5m l.

• Break rolls rotate at about 650 rpm, reduction rolls at about 500 rpm.

• Differentials speed: 2.5:1 to 1.5:1 in break & reduction rolls.

• Milling by-products (25% of grain): bran, germ, ‘clean out’ of cleaning house.

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Milling Machinery- Roller Flour Mill • Consists of two pairs of cast-iron rolls

mounted in a heavy cast-iron frame. Rolls have diameter of 225 to 250mm and lengths of 61 to 125 cm.

• Rotate in opposite directions at differential speed.

• Lower roll moves at lower speed than upper roller, thus shearing action is produced on grains.

• Break rolls have flutes or corrugations along length of roll, whereas reduction rolls have smooth surface.

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Milling Machinery- Stone Mill (Atta Chakki)

• Grain passes between a pair of stones

• One stone rotates while other remains stationary.

• Stones may be placed vertically or horizontally.

• Causes more damaged starch in flour.

• Mill stones frequently rub against each other resulting in small stone particles chipping off and mix into flour.

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Pin Mill Wheat grains are gravity fed through

centrally located inlet of mill .

Grain is passed through a pair of plates which have protruding pins.

One plate runs against a stationary plate.

Fine meal is then forced through screen by air due to high speed of plate rotation.

Varying rotor speed between a few hundred rpm to 5400 rpm provides flexibility to use the machine as a coarse grinding or a fine grinding mill. 32

Hammer Mill• Consists of swiveled metal blades that grind

grain by smashing it against a metal screen.

• Run at very high speed and fine meal is forced through screen by air due to high speed of hammers.

• A hammer mill contains a steel drum with a vertical or horizontal rotating shaft on which hammers are mounted.

• Rotor is spun at a high speed inside drum while material is fed into a feed hopper.

• Material is impacted by hammer bars and thereby grinding takes place and expelled through screens in the drum of a selected size. 33

Unit 2:WHEAT FLOUR CONSTITUENTS Flour Composition

Functionality of Flour Constituents

Proteins

Lipids

Starch

Enzymes

Manufacturing of Wheat Gluten

General Process

Industrial Process

Uses and Functionality of Gluten34

FLOUR COMPOSITION

Wheat flour is a complex mixture of starch, proteins, lipids, pentosans, enzymes and enzyme inhibitors and other minor components.

Flour Constituents Range

Moisture (%)

Ash (%)

Protein (%)

Lipids (%)

Wet gluten (%)

Dry gluten (%)

8.0-14.0

0.2-0.8

8.0-15.0

1.0-1.5

24.0-45.0

7.1-13.735

WHEAT PROTEINS IN FLOUR

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Classification of wheat gluten proteins

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• Native proteins of flour during mixing interact to form a chewing gum type of wet mass- “ wet gluten”.

• Gliadin becomes a viscous liquid when hydrated and imparts extensibility, allowing dough to rise during fermentation

• Glutenin provides elasticity and strength, preventing dough from being over-extended and collapsing either during fermentation or in baking.

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Role of Proteins in Bread Making

• Dough properties & bread making performance of flours are related to quantity and quality of proteins.

• Doughs that are too elastic and inextensible or vice versa give poorer bread making performance.

• Molecular size of proteins is also related with functional properties of flour.

• Glutenin proteins with longer mixing times have a higher average molecular weight than the glutenin proteins of short mixing flours.

• Flours with short mixing times give doughs that break down rapidly during mixing and easily extensible- unsuitable for bread. 39

Role of Proteins in Biscuits, Cakes & Cookies

Soft wheat with lower protein content produces flour suitable for cookie

Extensibility is a desirable for biscuit & cookie dough, gliadin proteins in flour is desirable.

Higher amounts of Glutenin make dough stronger and elastic, not suitable for sheet formation.

Higher proportion of gliadin and lesser glutenin proteins in flour is desirable for biscuit and cookie.

Cookie diameter & cake volume correlate positively with soft textured wheat (lower protein contents and smaller particle size).

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Lipids in Wheat flour

• Polar lipids are dominated by phospholipids and glyco- or galactolipids.

• Non-polar lipids are triglycerides, and they are solid at room temperature.

• Wheat flour lipids constitute about 2% by weight of flour but make important contribution to dough properties, baking behaviour and bread staling.

• Some lipids in wheat remain bound to starch component and thus such lipids are called starch lipids

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Role of Lipids in Bread Quality• Lipids interact with proteins of gluten complex and form large

aggregates which contribute to baking quality of wheat flours.

• Polar lipids improve texture and loaf volume of bread substantially, making bread softer and fresher.

• Polar lipids in association with surface-active proteins act as gas cell stabilizers. These create a thin layer of foam on interface of dough.

• Non-polar lipids (free fatty acids ) depress loaf volume of bread making it compact and less acceptable.

• Flour dough lacking in polar lipids develop large bubbles at early stage of oven baking & collapse due to instability of gas cells.

• Lipids prevent bread hardening by preventing retrogradation of starch molecules. 42

Role of Lipids in Biscuit, Cookies and Cake• Lipid extracted flour causes reduced spread and top grain

score in Cookies.

• Cookie spread and top grain score are improved as lipids are added to flour up to four times the natural level.

• Lipids have starch-binding action, when lipids are extracted from flour, starch gelatinization temp. is decreased and gelatinization of starch takes place in the early stages of baking which prevents spreading of cookies.

• Lipids play a role in foam production and stability of cake batter.

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Starch in wheat flour• It represents 65-75 % of flour.

• Starch particles are granules. A- granules & B-granules.

• Starch granules are composed of amylose & amylopectin.

• Amylose is a linear polymer of glucose linked by (14) glycosidic linkages.

• Amylopectin is a branched glucose polymer having (14) and (16) glycosidic linkages.

• Amylose: Amylopectin in wheat= 30 :70 .

Type of granule

Size Average Diameter (m)

% of Starch

% total of number of granule

A-granuleB-granule

BiggerSmaller

144

7525

1090

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Functions of Starch in Bakery Products Starch provides yeast fermentable sugars through the action

of amylases.

Starch-protein interactions contributes to stability of gas cells in bread baking. It helps in setting final texture of baked products.

Furnishes surface suitable for ‘anti-sticky’ proteins (friabilins) that affects hardness of grains.

Starch at temp. above 180C, gets converted into dextrin that undergo caramelization and contributes to crust colour of bakery products.

Starch dilutes gluten to desirable consistency, thus increasing starch content in flour increases diameter and spread of cookies.

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Gelatinization of starch in baked product Absorption of water by starch granules and its swelling

Change of shape and size of starch granules

Leaching of amylose or amylopectin from granules

Formation of a gel or a paste due to increase in viscosity

Setting of texture of bakery products during baking.

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Role of Damaged Starch in Bakery Products• Damaged starch is one that has been physically damaged

during wheat milling process .

• Wheat flour having higher proportion of damaged starch has higher amylolytic or diastatic activity.

• Lesser value causes poor gas production capacity of a flour, whereas higher value may lead to excess gas .

• Water holding capacity of damaged starch increases four times of normal starch.

• Desired level of damaged starch for bread production is 7-9%.

• For cookie & biscuit, damaged starch should be < 7%.

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Influence of Starch on Bread Staling• Bread staling refers to firming or hardening of bread during

storage.

• Staling rate is recorded max. at 4C.

• Retrogradation of starch contributes to hardening.

• Water level of 20 to 30% is required for retrogradation of starch. As bread contains 40% moisture, starch retrogradation occurs readily .

• Starch retrogradation changes A-pattern of native starch to B-pattern.

• Water holding capacity of B-pattern of starch is poor and hence breadcrumb looses water and becomes harder.

• Freshness of bread can be resumed on heating above 45C. 48

Role of Enzymes in Bakery Products

• Wheat grains contain a large number of enzymes.

• Many enzymes are found in aleurone, bran and germ.

• Flour rich in bran and dietary fibre may be rich in endogenous enzymes

• A combination of various enzymes have a positive effect on volume, colour, taste, aroma, crust and crumb texture, crumb softness, freshness and shelf life of baked product.

• Enzymes: Alpha-Amylase; Amyloglucosidase; Hemicellulase

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Alpha-amylase Alpha-amylase hydrolyses starch in to sugars, which are

fermented by yeast.

Enzyme- induced changes in dough rheology are also a major reason for increased bread volume.

Alpha-amylase also delays bread staling rate : it produces low molecular weight branched-chain starch polymers as hydrolysis products, which interfere with amylopectin recrystallization.

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Amyloglucosidase• This enzyme liberates glucose from chain ends and

capable of hydrolyzing branched starch molecules (amylopectin). It is used to give crust color and flavor as liberated glucose participates in Maillard reactions.

• Endoxylanase and exoxylanase (hemicellulase) use hemicellulose as a substrate.

• Hemicellulase hydrolyses arabinoxylan and releases water in dough. So, dough becomes softer, and its machine ability is improved.

• During baking, crumb formation is delayed, and better rise of dough in oven gives the bread larger volume and a softer, more delicate crumb.

Hemicellulase

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Manufacturing Techniques of Wheat Gluten

• Wheat gluten is water-insoluble complex protein, which is separated from wheat flours.

• Separation process is accomplished by physical means from aqueous flour suspensions without additives.

• In its freshly extracted wet form it is known as ‘gum gluten’ which when dried yields a cream coloured, free flowing powder of high protein content (75-80%) and bland taste.

• When rehydrated, it regains its original intrinsic viscoelastic properties, i.e. chewing gum like properties.

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Gluten manufature- general process

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Gluten manufature- Industrial Process• In Martin process: Dough is developed, then rested

under water and washed later with water.• In Raisio process: flour is just slurried with excess of

water and gluten seperated. • Martin process uses more water for separation of gluten,

hence affluent generation is more in this process.

Parameters LimitsProtein (dry basis)

Moisture

Ash

Fat (Ether Extracted)

Fibre

80% Min

10% Max

2.0%Max

2.0%Max

1.5%Max

International Standard for Wheat Gluten Powder

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Functionality of GlutenGluten has unique physical properties:

i. Viscoelastic properties improve dough strength, mixing tolerance and handling properties in a bread making process.

ii. Film forming property of hydrated gluten is a result of its elasticity. This ability of gluten enhances gas retention and controlled expansion for improved volume, uniformity and texture of baked products.

iii.Thermosetting properties contribute necessary structural rigidity and bite characteristics;

iv.High water absorption capacity improves baked product yield, softness and shelf-life.

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Uses of Gluten

The most fundamental use of vital wheat gluten is in adjustment of flour protein level.

In hamburger and hot dog buns: gluten can be used to improve strength of hinge.

In flaked cereals: gluten provides not only nutritional claims but also helps bind any vitamin-mineral enrichment components to cereal grain during processing.

Used in breakfast cereals, pasta, nutritional snacks, extruded ground meat products, textured protein, meat analogs and fabricated steaks.

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Unit 3: Dough Rheology

• Basic concepts

• Principles and measurement of dough rheology by – Recording dough mixers,

– Load extensio- meter

– Viscometer.

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DOUGH RHEOLOGY

Rheology is the study of deformation and flow of matter.

Dough Rheology - concerned with viscosity, deformation, and texture of dough.

Rheological properties determines behaviour of dough during mechanical handling; influences finished product quality.

Rheological tests:

Fundamental tests: for Viscosity and elasticity

Empirical tests : Mixograph; Farinograph; Extensiograph etc58

Basic concepts of dough mixing

Mixing curve showing hydration, development and break-down phases of wheat flour dough

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Physical properties of dough

1.Resistance to deformation

2.Extensibility

3.Elasticity

4.Stickiness

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Dough Rheology Instruments

1. Recording dough Mixers: measure the power needed to mix wheat dough and measure the resistance of dough to mixing blades

e.g. Farinograph and Mixograph.

2. Load extension meters: measures extensibility and resistance to extension of dough

e.g. Extensograph and Alveo-consistograph.

3. Viscometer: measures the viscosity of a wheat flour water suspension under standard condition of heating and cooling

e.g. Viscoamylograph. 61

Mixograph Mixograph may or may not be computerized.

Computerized Mixograph is suitable for analysing dough properties from a 2g flour sample.

Computerized Mixograph is supported by software ‘Mixsmart’ for automated collection of data and interpretation of results.

Mixing action: four vertical planetary pins revolve at a speed of 88 rpm around three stationary pins in the bottom of the bowl.

Power required to mix the dough is recorded. 62

Mixograph

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Mixing curve showing Mixograph parameters Mixing time = AB Peak dough resistance = AC Bandwidth at peak dough resistance = EFResistance breakdown = GCMixing stability = HIBandwidth breakdown = EF-HIWork input = ADB

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Mixograph Parameters and dough quality• Mixing time: A mixing time of 3-5 min is considered

suitable for bread. Flour having mixing time less than 3 min is suitable for biscuit and cookie.

• Peak Dough Resistance (PDR): has direct relationship with bread making quality of flour. Biscuit flour generally has lower PDR value.

• Bandwidth at PDR : A narrow width is an indication of dough ‘weakness’. Weak flour is recommended for biscuits and strong flour for bread making.

• Resistance and Bandwidth Breakdowns: Very steep left or right slopes of PDR are undesirable; indicates a flour with low mixing tolerance.

• Mixing Stability(MS): high MS desirable for bread , biscuit dough.

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• A Farinograph is a recording dough mixer.

• It measures resistance offered by dough against mixing blades operating at a constant speed and temp.

• Parameters obtained from resulting curve relate to amount of water required to reach a desired peak consistency.

• 2g to 300g of flour (14% oisture) is placed in Farinograph bowl. Water is added from a burette.

• As flour hydrates- dough develops- resistance on mixing blades increases- pen on chart recorder or curve on computer screen rises.

• Ensure that Farinograph bandwidth at max. resistance is always centered on 500 Brabender unit line (by adjusting amount of flour and water).

Farinograph

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Farinograph

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Interpretation of Farinograph Curve• Farinograph water absorption value: amount of water added to

balance the curve on 500-BU line, expressed as a percentage of flour. Water absorption value varies from about 50% for cookie and biscuit flour and around 60% for bread flour.

• Dough development time/mixing time/peak time: time between origin of curve and its max. it is the point at which dough is optimally developed and best able to retain gas.

• Mixing tolerance index: It is measured as difference (in Brabender units) between the top of curve at the max. and the point on the curve 5 minute later.

• Dough stability: It is defined as the difference in minutes between arrival time and departure time.

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Farinograph curve

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• It measures the extensibility and resistance to extension of fully mixed, relaxed flour-water dough.

• Force required to stretch the dough is automatically plotted against the distance it stretches to give extensograph curve.

• Dough is stretched under constant load and there is constant speed of moving hook, which stretches the dough.

Extensograph

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Procedure• Prepare dough in farinograph using 150g or 300 g of

flour, water and salt.

• Mix for 1 min, then allow to rest for 5 min, again mix for 2 min.

• Weigh 150 g dough and give it 20 revolutions in extensograph rounder. Roll it into a cylindrical piece in a shaping unit.

• Each dough cylinder is clamped in a cradle and allowed to rest for 45 min in a humidity chamber (at 30°C). Then, it is loaded on to extensograph and stretched.

• After test, same dough is reshaped as before, allowed resting for 45 min and stretched again. Generally 3 stretching curves obtained by repeating same procedure. 72

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Extensograph valuesExtensibility (E): Length of the curve in millimeters.

Resistance to extension (R): Height of extensograph in B.U. measured 5 cm after the curve has started.

Ratio figure: Ratio between resistance and extensibility i.e. R/E

Strength value: Area of curve - Measured by Planimeter. More the area, stronger is the dough.

Area under the curve (cm2) Dough strength

80 Weak

80-120 Medium strong

120-200 Strong

>200 Extra strong 74

Extensograph curve

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Alveo-consistograph

• It evaluates the strength of dough by measuring the force required to blow and break a bubble of dough.

• It is well suited for measuring the weak dough characteristics.

• Weak dough with low P value (strength of dough) and long L value (extensibility) is preferred for biscuits, cakes and other confectionery products.

• Strong dough flour have high P values and is preferred for breads.

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Procedure 100g flour is mixed with a salt solution to form dough. Five 4.5 cm circular dough sheets are formed and then rested in

alveograph in a temp.-regulated compartment at 25 C for 20 minutes.

Each dough sheet is tested individually. The alveoconsistograph blows air into a dough sheet, which expands into a bubble that eventually breaks.

Pressure inside the bubble is recorded. 

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Alveo-Consistograph Curve

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Alveoconsistograph values & dough qualityP Value: force required to blow the bubble of dough. indicated by

max height of curve and is expressed in mm. L Value: extensibility of dough before the bubble breaks.

indicated by length of curve and is expressed in mm. P/L Ratio: It is the balance between dough strength and

extensibility.W Value: area under curve. (combination of P value and L value)

and is expressed in joules. • Weak gluten flour has lower P values than strong gluten flour. • Stronger dough requires more force to blow and break the

bubble (higher P value). • A bigger bubble means the dough can stretch to a very thin

membrane before breaking. A bigger bubble indicates dough has higher extensibility. A bigger bubble requires more force and will have a greater area under the curve (W value).

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VISCOMETER- VISCOAMYLOGRAPH• This instrument measures amylase

activity by physical measurement of paste viscosity.

• Consists of heating system and a bowl (500 ml). has thermometer which is very sensitive and has mechanism for temp rise at rate of 1.5° C/min.

• Bowl has sensor to monitor temperature.

• As temp. rises, starch granules swell and viscosity begins to increase rapidly.

• Max. paste consistency obtained during gelatinization is used as a criterion of amylase activity of flour.

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Procedure Make smooth slurry of 100g flour and 360ml water in

beaker.

Pour slurry into viscoamylograph bowl. Rinse beaker with 100ml water and add to amylograph bowl.

Adjust starting temp to 30° C by hand, with clutch in natural position. Set clutch on increase temperature position and start viscoamylograph bowl in motion.

Viscosity of slurry is recorded on as temp rises from 30°C - 95°C. Read max viscosity in Brabender Unit (B.U.) at centers of peak.

Cooling system may be provided in viscoamylograph when temp reaches to 95° C, give holding period of 15 min and let temp come down to 50° C to record viscosity at different temperatures. 81

Evaluation of viscoamylograph curve

BU

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Thank you for attending the session

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