Food Industries Manual 007

7/29/2019 Food Industries Manual 007

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INTRODUCTIONIn this chapter, the progress of the raw materials,cereals, is followed through the various processingsteps, such as milling and baking, into finishedproducts. General quality factors are grouped atthe end of the chapter.

Since the last edition, the Bread and Flour Reg-ulations 1995 have removed the old definition fo rbrown flour, based on crude fibre content, buthave included hemicellulases as ingredients per-mitted in flour and bread. It is expected that allenzymes will be permitted as ingredients by theend of 1996 and that the bleaching agents benzoylperoxide and chlorine dioxide will cease to be per-mitted treatment agents by July 1997.

RAW MATERIALSWHEAT

CharacteristicsWheat grains are the fruit of the wheat plant,which is able to grow in most kinds of soil andunder widely differing climatic conditions. Theprincipal wheats of commerce belong to the bota-nical species Triticum aestivum and Triticumdurum; Triticum compactum or Club Wheat is notwidely grown now, but in the USA it is milled toproduce a soft flour for the manufacture of con-fectionery and biscuits.

A grain of wheat is ovoid in shape and bears atone end a number of short fine hairs, the beard.Down one side of the grain runs a deep longitu-dinal crease. The grain consists of three mainparts, the enveloping skins (bran), the embryo(germ) and the endosperm. The relative propor-tions of these parts vary with the plumpness of thegrain, but the average composition of wheat is83% endosperm, 2.5% embryo, 14.5% envelopingskins.

5 Cereals and Cereal Products

Raw materialsPage 172

MillingPage 181

FlourPage 184

BreadPage 192

CakesPage 195

OtherPage 198

BiscuitsPage 194

PastaPage 191

PackagingPage 199

Quality aspectsPage 200


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The enveloping skins are:(i) The pericarp, which consists of the epidermis,the epicarp and the endocarp. The pericarprepresents about 6% of the grain,(ii) The seed coat consisting of the testa and the

hyaline layer, which comprises about 2% ofthe grain,(iii) The aleurone layer representing about 6.5%of the grain.The composition of wheat varies quite widely,which is not unexpected in view of the many vari-eties that are grown and the very different condi-tions under which they are cultivated. The rangesof data normally encountered for commerciallytraded wheats are as follows:

Moisture 10.0-16.0%Protein 8.5-15.0%Fat 2.0-2.5%Fibre 2.0-2.5%Mineral matter 1.5-2.0%Sugars 2.0-3.0%Starch 63.0-71.0%Wheats are categorized as 'spring' or 'winter'according to sowing and growing conditions.Winter wheat is sown in the autumn and becauseof its longer growing period, will generally out-

yield spring-sown varieties. However, springwheats need to have been 'cold' before they willgerminate, but they are generally recognized as thebest breadmaking wheats, despite their shortgrowing cycle.Wheats can be classified as either red or whiteaccording to the colour of the bran. White wheatsare susceptible to premature sprouting, with conse-quent high amylase activity. They are not, there-fore, used widely in the northern hemisphere inbreakmaking grists.The protein content and protein quality, andhence the breadmaking quality, of different wheatsvary widely. Some wheats, such as Canadianspring wheats, contain a high quantity of strongproteins. Others, such as English wheat, contain alow quantity of weak protein. The British millerblends together strong and weak wheats so as toobtain a mixture suitable for milling into breadflour.

Aleurone layerThe aleurone cells of the wheat grain lie betweenthe endosperm, that is the starchy parenchyma,and one of the surrounding wheat skins known asthe nucellar layer. The aleurone layer in the wheatgrain consists of a simple layer of cubical cells.They are heavily walled and contain protein, bu t

not protein which gives rise to gluten whenadmixed with water. The outer bran layers of thewheat grain may have detrimental effects in bread-making, but there is evidence that the aleuronelayer can be included with endosperm in themilling of breadmaking flours.Embryo of wheatThe embryo is that portion of the wheat grainfrom which the new plant originates. It lies withinthe branny skins of the grain and is separatedfrom the endosperm by a membrane known as thescutellum. It is customary to separate the embryoduring the milling process and the product thusobtained, which consists of embryo plus brannyskins, is known as germ.

EndospermThe endosperm constitutes the bulk of the interiorof the wheat grain. It serves as the food supply forthe new plant until the rootlets and leaf shootshave developed sufficiently to be able to obtainthe required nutrients from the soil and by photo-synthesis in the leaf. About two-thirds of theendosperm is starch. The object of the millingprocess is to remove the endosperm from thewheat grain with the minimum contamination ofbran powder and germ.

OTHER CEREALSBarleyThe cultivation of barley (Hordeum spp.) reachesfar back into human history. Barley was used as abread grain by the ancient Greeks and Romans.Roman gladiators were known as the hordeariibecause their general food was barley. Bread madefrom barley and rye flour was the staple diet ofthe poor in England in the fifteenth century, w hilenobles ate wheaten bread.Barley has a husk which is difficult to removeand is largely indigestible. The husk and bran areusually removed by abrasion to produce pearledbarley. Barley flakes made from pearled barley canbe used as a flavouring ingredient in specialitybreads.Barley is widely used for malting, brewing intobeer and for distilling in whisky manufacture. Thecontrolled germination of barley produces malt forbrewing but the malted barley can be dried and


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milled into a malt flour for use in the productionof malt bread and other baked goods.

MaizeMaize (Zea mays) is known as 'corn' in America.It originated in America, where it is still widelygrown and is now cultivated as a crop in Africa,India, Australia and the warmer parts of Europe.The grain of maize is much larger than those ofother cereals and it is used industrially as a goodsource of starch, which is extracted by a wetmilling process. The principal types of maize are:dent (Z. mays indentata) and flint (Z. maysindurata), pod (Z. mays tunicatd), pop (Z. mayseverta), soft or flour (Z . mays amylacea), sweet (Z .mays saccharata) and waxy (Z. mays ceratina).

Dry milling of maize aims to obtain themaximum yield of grits (endosperm chunks), con-taining the least possible contamination with fa tand black specks from the tip cap. Dry millingshould also recover the maximum amount of germin the form of large particles with the maximumoil content (maize is steamed and then degermedin a pin mill); it should also produce the minimumquantity of fine maize flour. This maize flourshould not be confused with 'corn flour', the termused in the UK for maize starch obtained by thewet milling process.Maize grits from dry milling are used in theproduction of breakfast cereal and in extrusioncooking in the snack foods industry. In Italymaize porridge, made from fine grits or coarsemeal and flavoured with cheese, is called 'polenta'.Fine meal or maize cones are used for dustingbakery products like muffins, in bakery mixes orin infant foods.Maize has a characteristic flavour which ispopular in Mexico and the southern states of theUSA but is only just being introduced to theBritish public in Mexican restaurants specialisingin tortillas and tacos.

MilletMillet is a name given to numerous small seededgrasses which are of Asian or African origin. In1981, the world crop was estimated at 29 milliontonnes of which 40% was Pearl millet (Pennisetumamericanum) and 24% was Foxtail millet (Setariaitalicd). Another 25% of the world crop is madeup of two further types of millet, Proso (Panicummiliaceuni) and Finger (Eleusine coracand).The millets have been used as human food fo r

thousands of years in Asia, Africa and Europe.Their cultivation can be traced back into prehis-toric times, and in parts of India and Africa, theyare still a staple food. The traditional method forthe preparation of millet for domestic consump-tion is simply pounding in a mortar to loosen thehusk and to reduce the grain to a wholemeal orsemolina, followed by winnowing. Preparation oflarge quantities of meal is not practised because inhot climates the undegermed meal becomes rancidvery quickly.

The flour or millet meal can be used to makeunleavened bread, or the ground product may beused to make a beverage. Millet may be consumedin the form of porridge, or it may be cooked withsugar, peanuts or other foods to make desserts.The protein contents of pearl, foxtail and prosomillet are comparable with that of wheat andbarley but finger millet has a somewhat lowerprotein content, similar to the level in rice.Although the protein quality of millet is good andhas a higher lysine content than wheat, it does notform gluten. The lack of gluten makes it difficultto make unleavened pancakes (roti, chapatti ortortilla) from millet meal and cold water. The useof boiling water to make the dough results inpotential gelatinization of the starch and allowsthe dough to be rolled out into thin pancakeswithout breaking or tearing.

OatsOats (Avena saliva) are a crop of the temperateregions, but are not suitable for particularly dryor prolonged sub-zero Celsius conditions. Thekernel, which is called a groat, retains its husk onharvesting like rice and barley and has the charac-teristic cereal structure of endosperm, bran andgerm. Compared with other cereals, oats are char-acterized by a high protein and fat content and alow carbohydrate content. The high fat contentand naturally occurring fat-degrading enzymesprovide potential for rancidity in milled oat pro-ducts. However before oats are used for humanconsumption, the tightly adhering husk has to beremoved. This is normally carried out by an abra-sion process after the oats have been heat treated(kilned). This causes the husk to become friableand also inactivates the fat-degrading enzymes,thereby eliminating most of the potential fo r enzy-matic rancidity. After removal of the husks, theoats may be flaked, milled into flour or cut intosmaller pieces.

In the United Kingdom, oats have traditionallybeen used for porridge, oat cakes and biscuits.


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Since the mid-1980s, the market for oat flakes hasincreased with the increasing consumption ofmueslis. In more recent years, oats and oat branhave been used in an increasing number of pro-ducts. One of the reasons for this has been aclaimed link between the intake of soluble fibre,from oats an d particularly oat bran, and a reduc-tion in blood cholesterol level. This, in turn,reduces the chances of developing cholesterol-related heart diseases. There is, however, stillmuch debate about the validity of the cholesterol-reducing claims for oats.Naked oats are recently developed varieties inwhich there is no closely adherent husk on thekernel. Whilst various beneficial claims have beenmade, heat treatment will still be required to avoidrancidity. Wild oats are a different species toAvena sativa and can be a serious weed in crops ofcultivated oats and other cereals.

RiceRice (Oryza sativa) is generally considered to be asemi-aquatic annual grass, typically associatedwith paddy fields and tropical countries. However,there are varieties that have adapted to a widerange of environmental conditions from dry hill-sides to the foothills of the Alps and Andes,although rice is not grown in the extreme latitudeswhere wheat and barley are cultivated. Togetherwith wheat and maize, rice is one of the threemajor cereals of the world and is the basic foodfor over half the world's population. In somecountries, it provides 80% of the daily foodintake.After harvesting, rice kernels usually retain theirhusk and are known as paddy or rough rice.When the husk is removed it is called cargo orbrown rice. The kernel is of the typical cerealform, having endosperm, bran and germ, but isdifferent from wheat, in not having a longitudinalcrease. When rice is milled it is not ground up toproduce a flour, but goes through various degreesof abrasion to remove the bran and germ to givewhite rice. The white rice may then be polished togive it a brighter and smoother appearance and toenhance its cooking properties. As with othercereals, the bran and germ contain a significantproportion of vitamins and minerals which arelost on milling.Rice is varied in its properties and hence has awide range of uses and different quality prefer-ences throughout the world. In the UK, rice isprincipally used as a vegetable, as a dessert andfor breakfast cereals. There are three major types

of rice, long, medium and short grained, which areclassified by the grain shape and tend to have dif-ferent properties and hence different uses. In theUK, long grain rice in white or brown form,usually from the USA, is used as a vegetable andshort grained rice, usually from Italy, is used forrice puddings. Other categories of rice are:(i) Basmati rice. An aromatic long grainedtype, which only comes from the Himalayanfoothills in India and Pakistan.(ii) Parboiled rice. This is rice that has beensteeped, steamed and dried whilst still in itshusk. This process carries soluble vitaminsand minerals from the husk into the kernel,which following dehusking is more nutritious

than usual. The process also decreases thelikelihood of the kernels being sticky whencooked, bu t they will tend to be darker andrequire a longer cooking time than usual.(iii) Easy/quick cook rice. This has been pro-cessed to increase the rate of penetration ofwater into the kernel, hence decreasing thecooking time. The extreme of this is instantrice which only requires the addition ofboiling water.(iv) Wild rice. This is not a true rice, but anaquatic grass with long slender black-to-brown grains; it is used to add to long grainrice for its visual effect.RyeRye (Secale cereale) tends to be grown on landjust outside the belt which gives the most satisfac-tory return for wheat, such as areas of northernan d eastern Europe that have a temperate climate.As a bread grain, rye is second only to wheat inimportance and is the main bread grain of Scandi-navian and eastern European countries. Althoughnutritious and palatable to some people, rye breadis not comparable with wheaten bread as regardscrumb quality, large loaf volume or taste. Culti-vated rye was derived in about 400 BC from therye grass that occurred as a weed in wheat andbarley crops.Rye is particularly susceptible to infection bythe fungus Claviceps purpurea, which can alsoattack barley, oats and wheat. The sclerotia of thisfungus are known as ergot. Ergot is a toxic con-taminant of cereals, which has a maximum limitof 0.05% in wheat and rye traded within the Eur-opean Union.The grains of rye are longer and thinner thanthose of wheat and have a greenish-grey colour.Rye milling differs from wheat milling and usually


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involves the use of eight of more break rolls andcomparatively few reduction rolls. Rye meal andflour have a characteristically high amylase activityand its protein produces little gluten which limitsits use in bread production. The high pentosancontent of rye allows batters to be whipped fromwater and rye meal, which form a stable foam.These stable foams can be baked at high tempera-ture into crispbread.In order to avoid excessive amyloytic break-down of the starch in breadmaking, the pH of therye dough is lowered by acid modification in a'sour dough'process. A starter 'sour dough' is pre-pared by allowing a rye dough to stand at 250Cfor several hours to induce a natural lactic acidfermentation caused by species of Lactobacillus.Although rye bread is still no t popular in theUnited Kingdom, the successful new range of 'softgrain' breads, such as Mighty White, contain pre-soaked kibbled wheat and rye grains.

SorghumSorghum probably originated in Africa. Egyptianfrescoes suggest that it was in cultivation in 2200BC. All the cultivated sorghums are known asSorghum valgase or Sorghum bicolour. Grainsorghum is a coarse grass which bears loose pani-cles containing up to 2000 seeds per panicle. It isan important crop and the chief food grain inparts of Africa, China and the Indian subconti-nent, where it forms a large part of the humandiet.In the so-called 'waxy' type of sorghum, thestarch is composed almost entirely of amylopectin.These varieties have starch with physical proper-ties similar to those of cassava, from whichtapioca is prepared.The whole sorghum grain may be cooked likerice or fried. Acceptable bread products, such asmuffins or griddle cakes, can be produced froma blend of strong wheat flour and sorghumflour. Rollermills are not appropriate fo r proces-sing the round sorghum grain. The bran andgerm of sorghum pulverize easily to a finepowder which is difficult to separate from thefine flour. Dry milling is accomplished in twostages: an abrasive pearling to remove bran isfollowed by pulverizing the pearled grains. Wetmilling of sorghum to produce starch usesmethods similar to those employed fo r maize bu tthe process is more difficult. Varieties with darkcoloured outer layers are not satisfactory for wetmilling because some of the colour leaches ou tand stains the starch.

TriticaleTriticale is a polyploid hybrid cereal derived froma cross between wheat (Triticum) and rye (Secale).The first wheat-rye hybrid was described in 1876but it was nearly ninety years before the first hexa-ploid triticale varieties were released in Canada,Spain and Hungary.The objectives in making the cross were tocombine the grain quality, productivity anddisease resistance of wheat with the vigour andhardiness of rye. Varieties of triticale in commer-cial production prior to 1990 did not offer muchpromise for milling and baking; they resembledtheir rye parent more than their wheat parent, par-ticularly in a tendency towards undesirably higha-amylase activity and the inability to form anelastic gluten protein. Triticale can be milled onrollermills used for wheat milling, and baked pro-ducts made from triticale flour-wheat flour mix-tures can be purchased in Europe and NorthAmerica.

ADDITIVES

Ascorbic acidAscorbic acid (vitamin C, E300) acts as a flourimprover, and if used in the proportion of 20 to200 ppm of flour, it improves the baking qualitymaterially. It differs from other flour improvers inthat it is a reducing agent; however it is readilyoxidized by air to dehydroascorbic acid and it isthis compound which exerts the improving action.It is the only oxidative improver for use in themanufacture of bread, allowed by the UK Breadand Flour Regulations 1995. It finds its chief usein the shorter breadmaking processes, such as theChorleywood process, and is added by the bakerin a proprietary bread improver. In the UK itmay also added to the flour by the miller.

Benzoyl peroxideThe organic peroxide (C6H5CO)2O2 has beenwidely used as a flour bleacher. It gives an effec-tive bleach when added in the proportion of 1part to 30000 parts of flour, but the reaction isslow and needs about three days to reach comple-tion. Benzoyl peroxide has been used as a proprie-tary mixture in which it is diluted with about sixtimes its weight of inorganic fillers.Until July 1997, all bread and flour other thanwholemeal may contain benzoyl peroxide in any


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proportion not exceeding 50 ppm. However, from1996 onwards, most white flour milled in the UKwill be unbleached.Bleaching agentsAt one time flour was always 'aged' for severalweeks before it was despatched to a baker andduring this period it improved significantly inbaking quality and became bleached. For manyyears both the improving and bleaching effectshave been attained rapidly by adding smallamounts of oxidizing agents to flour. Thebleaching agents used had no action on thebranny particles an d consequently did not make adull or inferior flour seem to be of better grade,they only removed the yellowness, which is presentin even the highest grade of flour, and so yieldedthe white bread which was thought to bedemanded by the public. In 1996, the substanceswhich are permitted in the UK as flour bleachersare chlorine dioxide, benzoyl peroxide andchlorine, although the latter chemical is legallyrestricted to use in cake flours. Both benzoyl per-oxide and chlorine dioxide will be banned fromJuly 1997.ChalkWhen the rate of extraction of flour was raised to85% during World War II, millers were instructedto add prepared chalk of British Pharmacopoeia(BP) quality to all flour in order to compensatefor the calcium-immobilizing effect of the phyticacid present in the longer extraction flour. The BPname for such material was 'creta praeparata' an dsome millers still refer to 'creta'. The UK Breadand Flour Regulations 1995 require the additionof prepared chalk of BP quality and of a stateddegree of fineness to all flours other than self-raising flour with a calcium content of not lessthan 0.2%, wholemeal and wheat malt flour. Theflour should contain not less than 235 mg and notmore than 390 mg of chalk per 100 g of flour. Theaddition is now no longer made to counteract theeffect of phytic acid, which is very small in whiteflour, but as a means of supplementing calcium inthe national diet.Chlorine dioxideChlorine dioxide is a gaseous flour improver andbleach that superseded Agene (nitrogen tri-chloride) in Britain and in the USA. Plants were

available that enabled it, greatly diluted with air,to be added continuously and automatically toflour in a precisely controlled proportion. Anormal rate of treatment in Britain was about 15ppm. However the major production streams froma flour mill were treated with different rates ofchlorine dioxide. The 'patent stream' requiredleast treatment and the 'low grade' streamrequired most bleaching and improving.The reaction against the use of additivesdescribed under BENZOYL PEROXIDE also appliesto chlorine dioxide and by July 1997, at the latest,chlorine dioxide (Dyox) will not be used by Britishmillers.

ChlorineChlorine is used in the production of specialitycake flours. These are finely dressed flours milledfrom a weak wheat of low protein content, whichhave been treated with chlorine at the rate of 1500ppm.Fungal amylasesFor many years it was customary for the miller tocorrect diastatic insufficiency in a bread flour bythe addition of malt flour as a source of a-amylase. During the last few years, however, therehas been a growing tendency for malt flour to besuperseded by fungal oc-amylases for this purpose.Fungal a-amylases are obtained by growingAspergillus oryzae in deep culture and extractingand purifying the oc-amylase that accumulates inthe culture medium. The purified enzyme is sui-tably diluted with a carrier so that the necessarydiastatic correction can be attained by supple-menting a flour with abou t 100 ppm of themixture.Fungal a-amylase preparations have severaladvantages over malt flour as diastatic correctives.These include:(i) Freedom from other and possibly undesirableenzymes, e.g. bacterial amylase, which cansurvive the baking process,(ii) Standardized potency,(iii) Low temperature of inhibition, which avoidsstickiness in the crumb in the event of overdo-sage.IronThe UK Bread and Flour Regulations 1995require that in the UK white flour shall containnot less than 1.65 mg of iron per 100 g. At present


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iron may be added as ferric ammonium citrate ofBP or BP Codex quality or as finely divided iron.Some forms of ferric ammonium citrate cause thedevelopment of rancidity in the master mix onstorage and for this and other reasons the iron isalmost invariably added as finely divided iron.However, evidence is accumulating that the assimi-lation of finely divided iron is far from completeand in future salts of iron may be the preferredmeans of enrichment.

RAISING AGENTSAcid calcium phosphateAcid calcium phosphate (ACP, Ca(H2PO4)2) hasbeen used effectively as a preventive of the bacter-iological spoilage of bread known as 'rope' (seeROPE). This compound has an inhibiting action onamylases and has been recommended as an ameli-orative measure in combating sticky bread crumband problems encountered when slicing bread inplant bakery. Acid calcium phosphate is widelyused in the milling industry as the acid ingredientin self-raising flour. Its neutralizing value, i.e. theparts of sodium bicarbonate that would be neutra-lized by 100 parts of the phosphate, varies withthe sample, the usual value being about 80.Acid calcium phosphate coated with sodiumphosphate or other phosphates is widely used inthe USA. It acts more slowly on sodium bicarbo-nate in the cold than does ordinary acid calciumphosphate and hence gives rise to less loss of gasfrom self-raising doughs during the prebakingperiod. In Northern Ireland, acid calcium phos-phate is added to 'plain' flour to cater for localtaste and particularly for the production of hotplate goods such as farls.

Acid sodium pyrophosphateAcid sodium pyrophosphate (ASP, Na2H2P2O7),which is used as an acid ingredient in bakingpowders and also in self-raising flours, is availableundiluted. It is also marketed diluted with a filler(usually dried starch) to a concentration of 64%,at which level 2 parts of the mixture will neutralize1 part of sodium bicarbonate. Acid sodium pyro-phosphate reacts more slowly with sodium bicar-bonate than does acid calcium phosphate andhence leads to less loss of gas from self-raisingdoughs during the prebaking period. Baked goodsproduced from self-raising doughs containing acidsodium pyrophosphate may, however, possess a

tang or 'bite'. There is, therefore, much to be saidfor the Use of a mixture of acid sodium pyrophos-phate and acid calcium phosphate and such amixture is available on the market.

Baking powdersBaking powders are mixtures containing chemicalsused for the aeration of various types of bakeryproducts. The active ingredients are sodium bicar-bonate and an acid substance, which in the pre-sence of water, and with or without heat, willreact to produce carbon dioxide. The relative por-tions of bicarbonate and acid are such that theyalmost exactly neutralize each other but an adjust-ment may be made so that the resulting product isintentionally slightly acid or alkaline. The two che-micals are dispersed in an inert filler such asstarch.The acid components mainly used in bakingpowders are acid sodium pyrophosphate, acidcalcium phosphate, cream of tartar, glucono-5-lactone and sodium aluminium phosphate. Eachof these has its own characteristic effect, e.g. onflavour or speed or slowness in working off.

Cream powderA cream powder is a preparation containing anacid phosphate to replace cream of tartar inbaking powders. Its neutralizing value is adjustedby dilution with flour to be equivalent to that ofpure cream of tartar, which is much more expen-sive. The common phosphates used are acidcalcium phosphate and sodium pyrophosphate.They have the advantage that they do not act onthe bicarbonate in the cold. It is claimed thatsodium aluminium phosphate has an even moredelayed action than the other tw o phosphatesmentioned. The disadvantage of the acid calciumphosphate is that when it is present in excess ofthe sodium bicarbonate it produces an acid bite,and unless they are very finely ground, the parti-cles will tend to produce brown spots on thesurface of sugar-containing products.

Sodium pyrophosphate is said to improvegluten by making it more extensible.

Cream of tartarCream of tartar, potassium hydrogen tartrate, isused as an acid ingredient in some bakingpowders. It has the disadvantage of working off


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quickly and has been replaced by a range ofcheaper acid phosphates which, however, do notproduce such a satisfactory flavour in the finishedproduct.One hundred parts of cream of tartar will neu-tralize 45 parts of sodium bicarbonate so that theusual 2:1 mix for baking powder will give aproduct slightly on the alkaline side.

Glucono-5-lactoneGlucono-8-lactone is the lactone of gluconic acid.It is used as an acid in raising agents for tworeasons, first, it does not have the distinctive biteof sodium pyrophosphate and second it is onlyconverted slowly to the active state when it comesinto contact with moisture and thus delays theworking off of mixed batters, for example. It is,however, mo re expensive than the more commonlyused acidulents.

Sodium bicarbonateSodium bicarbonate is the gas producer in bakingpowders and in self-raising flours. Carbon dioxideis released when it reacts with an acid and thebalance of bicarbonate to acid needs to beadjusted so that normally the final product finishesup just on the acid side of neutral. Sodium bicar-bonate will release its carbon dioxide simply bythe action of heat, but in the absence of acid, theresidue is very alkaline. This no t only produces anunpleasant flavour but causes the crumb of pro-ducts to turn yellow.

PRESERVATIVESIn bread, the following substances may be addedas preservatives: acetic acid, monocalcium phos-phate (ACP), sodium diacetate and propionic acidand certain of its salts. All these help to preventthe onset of 'rope' but the propionates also havean antimould effect.

Acetic acidA 12% aqueous solution of acetic acid, at the rateof 0.5 1 per 100 kg of flour, m ay be used as a pre-ventive against the development of 'rope' in bread.The purpose of adding the acid is to reduce thepH of the crumb to below 5.4.

Propionic acid and propionatesIn the EU, propionates are allowed in bread (butnot in biscuits) up to 3000 ppm of the flour weightand they are used at this, and sometimes higherlevels, in other countries also. There is a flavourbreakthrough at this level and in the UK it ismore usual in practice to use propionates at about1000 ppm. Under normal conditions, this will givean extra 24 h shelf life to wrapped bread before itgoes mouldy. Propionates have a delaying effecton yeast and where they are used, this must beallowed for by adding extra yeast.During 1986, the pressure for 'healthier' foodsled to bakers removing propionate from bread sothat they could add the claim 'free from preserva-tives' to their wrappers. However, the shortenedmould-free shelf life has not pleased all consu-mers.

Sorbic acid and sorbatesSorbates are more effective mould inhibitors thanpropionates. They also have a delaying effect onyeast which must be allowed for in the manufac-turing process.

PROCESS INGREDIENTS

Ammonium carbonateCommercial ammonium carbonate, which is amixture of ammonium bicarbonate and ammo-nium carbamate, is known as 'VoI' in the bakingtrade. Under the action of heat it decomposes tocarbon dioxide, ammonia and steam and thus actsas an aerating agent. It is used mainly in biscuitmanufacture. It has the advantage of leaving noresidue in the finished product but the disadvan-tage that freshly baked goods made with it have asmell of ammonia although this quickly disap-pears.

Ammonium chloride and sulphateAmmonium chloride and ammonium sulphatehave been used as yeast foods, being readily avail-able sources of nitrogen for the organism. One orthe other was used as an ingredient in most com-mercial bread improvers, but yeast foods are notnecessary in a modern dough conditioner whichcontains mixed enzyme systems and emulsifiers.


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Improvers or dough conditionersThe breadmaking quality of freshly milled whiteflour improves with age due to the action ofatmospheric oxygen; the gluten is rendered morestable and stronger and also more elastic. At onetime millers never despatched flour to a bakeruntil it had been stored for several weeks andthus had undergone this natural 'ageing'. Later, itwas discovered that this delay could be avoidedand the effects of natural ageing attainedpromptly by adding a very small amount ofammonium persulphate to the flour. Subsequentlyit was found that a number of other oxidizingsubstances were able to age flour artificially. Itbecame common practice in the milling industryto treat all breadmaking flour with improvers, asthey are called, in order to obtain the improve-ment in breadmaking quality which previouslyused to be obtained by ageing freshly milledwhite flour for several weeks. The improvementconsists of rendering the gluten more stable andstronger and also more elastic. Some improversbleached the yellow pigments of flour as well asimproving the baking quality, but others had nosuch bleaching effect. When the latter were used,the miller added a bleaching agent to the flour,in order to reproduce the change from creaminessto whiteness that accompanies natural ageing.Since 1989,when potassium bromate was banned,the only oxidative improvers that are used inBritain are ascorbic acid and chlorine dioxide.Chlorine dioxide also has a bleaching effect, bu tascorbic acid acts only as an improver. FromJuly 1997,chlorine dioxide will not be allowed inBritish mills.The mode of action of improvers has been thesubject of numerous investigations and several the-ories have been advanced to explain their benefi-cial effect. The weight of the evidence is in favourof an increase in the cross-linkages between neigh-bouring protein molecules by oxidation of contig-uous sulphydryl groups to form new disulphidebonds.Commercially nowadays the term 'improver' isapplied to an all-in mix containing all or some ofthe following: flour improvers, yeast foods, fats,emulsifiers, enzyme preparations, soya flour, aflour filler and possibly calcium propionate. Themix of ingredients will depend on the intendeduse. It may also contain calcium sulphate andammonium sulphate as yeast food. The hard fatessential for the process is suitably dispersed, pos-sibly on an enzyme preparation such as malt flouror , more commonly, fungal amylase, hemicellulaseand some inert filler. Bread improvers are usually

designed to be used at 1% or 2% of the flourweight.

Glyceryl monostearateGlycerol (glycerine) is a trihydric alcohol andwhen each molecule of glycerol is combined withthree molecules of fatty acid, either the same ordifferent acids, the result is a fat. Glyceryl mono-stearate (GMS) is obtained when glycerol is com-bined with only one molecule of fatty acid, stearicacid. This produces a molecule with glycerol,which is water soluble (hydrophilic) at one end,and a fat, which is oil soluble (lyophilic), at theother. This configuration confers emulsifying prop-erties on GMS. To be effective in emulsificationand for crumb softening, the GMS should be pre-sented in the correct crystalline form and as ahydrate. Commercially available solid GMS isgenerally a mixture of GMS (33%), glyceryl dis-tearate and stearin, bu t distilled GM S (90%) isavailable, and also prepared stabilized hydrate.

LecithinsLecithins are emulsifiers occurring naturally, forexample, in egg yolk and the soya bean. Commer-cial lecithin is extracted from soya bean as a verysticky yellow paste which is difficult to handle andit is now more usual to buy it dispersed on a sui-table support. When lecithin is used at 0.5% offlour weight in bread, a silkier softer crumb isclaimed. It is used more on the continent than inthe UK where it appears to have lost ground tothe newer emulsifiers and crumb softeners.

ShorteningsWhen vegetable or animal oils are hydrogenated,their melting points are raised, producing fats orshortenings. The degree of hydrogenation andtherefore the melting points of the product may bevaried. Like oils, shortenings are a mixture ofmany triglycerides of different melting points.

Ideally the proportion of fat with a meltingpoint above that of body temperature needs to becontrolled, otherwise, on eating, the presence ofthe high melting point fraction becomes apparentin the mouth as a 'palate cling'. This is notobvious when a product is eaten hot. Some tai-lored shortenings for puff pastry have greater pro-portions of these higher meltiiig point fats so thatthe layers of fat are not dispersed in preparing the


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pastry. Shortenings used in recipes containinghigher weights of sugar and liquor than flour, socalled high ratio shortenings, have emulsifyingagents such as glyceryl monostearate incorporatedin them. Because of the hydrogenation, shorten-ings are more stable and resistant to air oxidationthan their parent oils.Soya flourSoya flour is milled from the soya bean, a legumewidely grown around the world. The UK is toofar north fo r existing varieties of soya bean tocrop successfully and beans milled in the UKusually come from North America. Commercialsoya flour exists in two forms, raw enzyme-activeflour and an enzyme-inactive flour milled fromheat treated beans.Raw soya was once added (up to about 2%) tomost plant made bread, but now it is normallyonly added as an ingredient of commercial breadimprovers. Various advantages for its addition tobread have been claimed but possibly the onlyimportant one is its whitening effect on the crumbdue to the bleaching effect of the lipoxidasepresent; because of this and the pressure toremove chemical bleaching agents, e.g. benzoylperoxide, an increase in its use for this purposemay be anticipated. The enzyme-inactive flour isused in cake pastry and biscuit formulations.Soya flour is rich in protein (about 40%) andoil (about 23%) and the defatted flour is used asfeedstock in the preparation of texturized vege-table protein.

SaltSalt is an important ingredient of bread, withoutwhich the product appears to have little flavour.However, the 1991 COMA (Committee onMedical Aspects of Food Policy) report hasrecommended that the salt intake of the UKpopulation should be reduced. Experimentsshowed that salt levels in bread could be reducedby up to 12.5% without it being detectable bytaste and most bakers have taken this action. Thisdoes not mean that all bread has the same saltcontent and regional differences still exist, e.g.southern England 1.1% and Scotland 1.2%.YeastThere are several hundred species of yeast. Baker'syeast is the species Saccharomyces cerevisiae. It is

a single cell organism roughly oval in shape andmeasuring about 4 mm in length.

Commercial yeast is grown on a sterilizedmolasses feed stock, first anaerobically and finallyaerobically with air being blown through the fer-menters. It is normally sold in a compressed blockform containing about 30% solids. Granularyeast, which contains rather less moisture, is nownot so popular in the UK although it is still usedin some European countries. Cream yeast, a liquidcontaining about 20% yeast, has the advantagethat it can be pumped and metered in continuousprocesses. Dried yeast might be considered auseful standby in case supplies of fresh yeastshould be interrupted but considerably more yeasthas to be used to achieve the same gassingactivity. Commercial yeast is the result of muchdevelopment work to obtain an all-purposeproduct and that in the UK is generally fasteracting than those used elsewhere.

Yeast works by converting the fermentable car-bohydrates in the dough into alcohol and carbondioxide, the latter producing the required aerationin the production of bread. The contribution thatyeast makes to the flavour of bread is important.The activity of yeast increases with temperature toan optimum at about 4O0C and above this tem-perature the activity quickly drops off until 5O0Cwhen all the yeast cells are killed. Yeast is a liveproduct and must be treated as a perishable com-modity - ideally it should be stored between I0Cand 40C. Yeast stored in a warm bakery willquickly lose its acitivity. More detail is given byBrown (1982).

Baker's yeast contains a very complex enzymesystem. The enzymes of importance to the bakerare invertase, converting sucrose to fructose andglucose; maltase, converting maltose to glucose;and zymase, converting glucose and fructose intoethyl alcohol and carbon dioxide. Recently anunwanted enzyme appeared in some commercialstrains which reduced the flavouring principle ofcinnamon, cinnamic aldehyde, to styrene, themonomer of polystyrene, thus producing a strongplastic flavour in spiced buns.

PRIMARY PROCESSESMILLINGThe wheat grain consists of three parts, the envel-oping skins, the embryo or germ and the endo-sperm. The object of the milling processs is toseparate most of the endosperm in a manner thatleads to minimum contamination with powdered


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Figure 5.1 Flour milling process.skins and germs. The operations included in theconversion of wheat into white flour are cleaning,conditioning, breaking, scalping, purification andreduction. A schematic diagram of a typicalmilling process is shown in Figure 5.1.

CleaningThe wheat is subjected to a number of sievingoperations to remoye impurities larger or smallerthan the grain. It is passed through disc separa-

tors to remove other cereals such as barley andoats and other impurities which are similar towheat in diameter but different in shape. Thewheat is then scoured and brushed in order toremove dirt and the thin papery pericarp which iscalled 'beeswing'. During these operations thegrain is subjected to aspiration to remove lightgrains and seeds, 'beeswing' and dust. Heavymaterial such as stones which are of similar sizeto wheat grains are removed on a gravity tableand metal detectors or magnets remove iron andswarf.

Raw materialsCleaning Conditioning Water

GristingIntakeBreakrolls Sievesandpurifiers

ReductionrollsSieves

U p to12 reductionstagesU p tofour breakstagesOffal

Germlour

Packingagged flour

Bran


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ConditioningThe objects of the conditioning process are totoughen the bran, to enable the bran an d endo-sperm to be separated easily, to facilitate the pul-verization of the separated endosperm, to enablethe products of the flour dressers to be sievedeasily and accurately and to arrive at a correctmoisture content in the finished products. Themoisture content of dry wheats has to be increasedand this is accomplished by preliminary dampingand subsequent conditioning. Proper distributionof the added moisture is achieved by allowing themoist wheat to lie in a bin for 4-36 h, but morecommonly nowadays water is added in a machinewhich tumbles the grain through high pressurewater sprays and this efficient wetting processenables the conditioning time to be reduced.British wheat is often too moist for optimummilling and hence requires drying before it can beaccepted into the mill.BreakingThe breaking stage of the milling process is per-formed by a series of pairs of corrugated rolls,known as break rolls, which revolve in oppositedirections at a differential speed of 2.5 to 1. It iscommon practice to have four pairs of break rolls,each pair having finer corrugations and a smallerclearance than the preceding pair.The corrugations and the differential speed givethe break rolls a shearing action and their purposeis to split open the grains and scrape the endo-sperm from the branny skins. After passingthrough the first break rolls, the material is sievedand the coarsest fraction, consisting of split-opengrains from which a little endosperm has beenremoved, goes to the second break rolls. Here thescraping away of endosperm is carried further; themixture leaving the rolls is sieved and the coarsestmaterial sent to the third break. More endospermis scraped away and removed by sieving and theresidue then goes to the fourth break rolls foranother, and often the final, scraping. The mate-rial that remains when the last scraping ha s beenperformed consists of flakes of the outer skins ofthe wheat bearing a small proportion of endo-sperm. This product is bran, which can be furthercleaned in a drum sieve or bran finisher.Scalping and gradingScalping is the name given to the sieving operationthat is performed upon the stock or chop, as it is

often called, that leaves a pair of break rolls. Theobject of this sieving is to separate the stock intothree main products: (i) coarse particles, which arethe remains of the grains and from which endo-sperm can still be obtained, (ii) flour and (iii) par-ticles of intermediate granularity, which arenodules of endosperm and are known as semolinaor middlings, according to their particle size andpurity. Scalping is usually performed by plansifterswhich consist of a number of superimposedenclosed horizontal sieving surfaces to which isimparted a rotary motion. The nests of sieves arehung on sets of flexible canes and they are giventheir rotary motion by a vertical shaft attached tothe middle of the machine and supported by anoverhead bearing. Most mills also employ plansif-ters as flour dressers at the end of the main flourcollecting conveyor.

PurificationThe semolina and middlings that have beenremoved from the various break stocks by scalpingare treated on machines known as purifiers. Theseconsist of enclosed reciprocating sieves throughwhich a current of air is blown. The combinedeffect of the aspiration and the movement on thesieves is to remove much of the loose brannymaterial with which the stock may be contami-nated and to grade the stock on the basis of par-ticle size and, to some extent, of purity.

ReductionThe purified semolina and middlings are sent tosmooth rolls, known as reduction rolls whichrevolve at a differential speed of 1.5 to 1. Theclearance of these rolls is adjusted to suit the gran-ularity of the stock fed to them. There will befrom 10 to 15 sets of reduction rolls in a mill.They are designated by consecutive letters of thealphabet (excluding I), and the later the codeletter of a roll occurs in the alphabet the lower thegrade of the stock with which the roll deals.The crushing action of the reduction rollsreduces the size of the nodules of endosperm inthe stock, reducing some of them to the finenessof flour, and at the same time tends to flatten outbranny and germy particles. The stock leaving apair of reduction rolls is sieved, or dressed as it iscalled, on plansifters, so as to remove the flourthat has been produced by the rolls. The residue isseparated into tw o fractions; the finer and purerof these goes to one of the succeeding reduction


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rolls, while the coarser and more branny materialgoes still further down the reduction system. Therolling action of the smooth, head reduction rolls,whilst flattening the bran particles in the desiredmanner, does inevitably produce some endospermflakes. In modern mills flake disrupters (highspeed phi mills) are installed after the rolls andbefore the sifters to increase the flour release.By the time the last reduction roll of the serieshas done its work, most of the endosperm hasbeen converted to flour and most of the coarserbranny fragments have been removed. The residueis an intimate mixture of endosperm and equallyfine branny matter from which it is no longerpracticable to separate good flour.DividesThe dressing machines in the mill furnish streamsof flour which differ from one another in colourand baking quality. All these streams may bemixed together to constitute straight-run flour, orthey may be segregated into several groups or'divides' which differ in grade and can be sold bythe miller as flours for different end products. Fo rexample, a brightly coloured high grade 'Patent'flour for the production of high quality bread androlls could be milled on a 40% divide from abreadmaking grist of 12% protein content, withthe remaining high protein flour being used toproduce malt bread.EntoletionThe Entoleter is designed to destroy all forms ofinsect life in flour and other cereal products.Internally it consists of two horizontal steel discs,each of which carries at right angles to its surfacea number of cylindrical steel rods. One of thesediscs remains stationary, while the other revolvesat 2000-3500 rpm. The stock to be treated is fedinto the middle of the upper and moving plateand thus thrown by centrifugal action toward theperiphery. On its passage to the periphery theflour is violently impacted against the cylindricalrods whereby all forms of insect life are destroyed.

FlakingCereals and malted grains can be milled intoflakes by crushing the moist grain through heatedmetal rolls. Flaked maize can be used as animalfeed. Flaked cereals are used extensively in theproduction of breakfast cereals.

RoastingDry drum roasting of cereals or malted grains no tonly dries the product but also imparts a charac-teristic taste and flavour. Roasting cereals underinfrared heaters is known as 'micronization' ofgrain and results in expanded products which areeasier for animals to digest and which can be usedin human foods such as muesli.

Wet miltingMaize is dry milled to produce grist for brewingor for the production of breakfast cereals, but awet milling operation is used to extract starch(cornflour) from maize.

PearlingGrains with a tightly adhering husk, such as rice,oats and barley, normally have the husk removedby an abrasion process known as pearling.

PRIMARY PRODUCTSFLOUR AND RELATED PRODUCTSWholemealWholemeal must contain the whole of the productderived from the milling of cleaned wheat.

Wheat flour, white flourFlour is the primary product obtained from themilling of wheat by the gradual reduction system.The object of this milling process is to separate, ascleanly as possible, the endosperm of the grainfrom the enveloping skins and embryo. How effec-tively this separation can be performed in a givenmill is a measure of its efficiency.The term flour extraction rate is used to denotethe proportion of flour obtained from wheatduring the milling process. The numerical magni-tude of the degree of extraction will depend on thebasis upon which it is calculated. The extractioncan be based upon (i) dirty wheat to silos, (ii)cleaned wheat to first break, (iii) total en d pro-ducts including screenings, and (iv) end productsless screenings. Method (iv) is the most usuallyemployed in Britain.The wheat grain contains about 82% of white


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starchy endosperm and so theoretically it is pos-sible to produce white flour of 82% extraction. Inpractice 80% is about the limit of white flourextraction and most commercial white flours arearound 77% extraction.Flour is produced from wheat in stages andwhen all the separated fractions are mixedtogether the resulting mixture is known as 'straightrun flour'. A divide consisting of a few of theflour fractions separated early in the millingsystem, thus only slightly contaminated with branpowder, is known as a 'patent flour' and sells at ahigher price than the 'straight run flour'. Bread-making flour in the UK is milled from selectedhome grown wheats alone or blends containing aproportion of strong wheat from North America,and has a protein content of 10.5-12.5%. Its dia-static activity should be sufficient to provide amplesugar for the yeast throughout the fermentation ofthe dough. It has been customary to add an oxida-tive improver to bread flour to enhance its bread-making quality and to bleach it to meet the publicdemand for white bread.Flour sold for domestic use may be less strongand less proteinous and consequently may be pro-duced from blends of European or other weak

wheats. A protein content of 9.5-10.5% would besuitable. Such flour is not always bleached andoften contains no oxidative improver.

Biscuit flourA biscuit flour should be weak and have a lowprotein content, 8.5% or less. The protein shouldhave good extensibility. For some formulations inwhich the biscuit dough needs to be very exten-sible, flour is treated at the mill with sulphurdioxide. It can best be made from a weak Britishwheat.

Cake flourCake flours used for recipes with high sugar andhigh liquor contents are designed to contain themajority of particles in the 15-55 ^m range, thusmaximizing the amount of large undamagedstarch granules. To achieve this narrow size range,flour particles are reduced in size by milling in apin or impact mill which minimizes the amount ofstarch damage. A modern cake flour plant wouldnormally consist of a system of pin mills with airclassification stages following each milling process.Speciality cake flours may also be treated withchlorine to aid cake stability.

Brown flourBrown flour differs from white flour in that it con-tains a relatively high proportion of bran, but itdoes not represent the whole of the grain fromwhich it was produced. If all the endosperm, germand all the skins of the grain were present, theproduct would be a wholemeal. Brown floursdiffer not only in bran content but also in granu-larity; in some bro wn flours, the bran is finelyground and in others it is present as relativelylarge fragments.Most meals are produced in the mill by runningtogether in suitable proportions stocks that inadmixture give a product with the desired charac-teristics. Whatever the method of manufacture, thewheat blend should be a strong one if the meal isto be used for the production of brown breads.Meals milled from home grown wheats are usedfor the production of 'wheatmeaF biscuits.The UK Bread and Flour Regulations 1984required that brown flours should contain not lessthan 0.6% of crude fibre on dry basis. In the 1995version of the Regulations, brown breads andflour have been removed as defined products.However, custom and practise would refer back tothe 1984 defin ition.Patent flourFlours milled from the head of the reductionsystem, which have been processed from thecleanest semolina, representing the centre of thewheat endosperm, are known as 'patent flours'.These patent flours are very bright in colour andare used in the production of high class confec-tionery and morning goods (rolls, etc.) wherebrightness of crumb is desired.

Air classified flourWheat flour may be further processed into speci-ality flours of defined particle size and proteincontent by air classification. Conventional sievingcannot be used to separate particles below 80 jimin size but fine particles can be classified by aprocess in which the effect of centrifugal force isopposed by the effect of air drag on individualparticles. The cut size at which the separation ismade can be adjusted, for example, by altering thevolume of air or its direction of travel.Free wedge protein, in which starch granules areembedded in the wheat endosperm, is found inflour as approximatley triangular pieces which are


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normally smaller than 17 jim in size. This intersti-tial protein can be removed from flour by air clas-sification, together with small B starch granulesand fragments of damaged starch granules. Cakeflours, particularly those used for the manufactureof sponges, need to be low in protein content andlow in starch damage. Therefore large and fineparticles may be removed from a flour by air clas-sification to improve its sponge-cake making prop-erties.SemolinaSemolina is nodules of wheat endosperm, some ofwhich carry particles of adhering bran. This millstock is produced on the break rolls and after pur-ification and grading is ground into flour. Purifiedsemolina is sold as a commodity or for processinginto pasta. The best quality pasta is made fromsemolina milled from durum wheat.Self-raising flourSelf-raising flour is flour into which sodium bicar-bonate has been incorporated and a water-solubleacid substance in such proportions that if they arepermitted to react will yield sufficient carbondioxide for aeration purposes without leaving amarked excess of either ingredient. Most self-raising flours contain 1.16% sodium bicarbonateand about 1.52% of 80% acid calcium phosphate.In some instances a mixture of acid calcium phos-phate and acid sodium pyrophosphate is used asthe acid ingredient. The presence in the self-raisingflour of 1.16% sodium bicarbonate and sufficientacid body to neutralize this gives the flour anavailable carbon dioxide content of about 0.59%,which is well above the statutory minimumrequirement of 0.40% and provides a good marginfor loss during storage.Since chemically aerated goods are bakedshortly after the dough has been made, there is noopportunity for the gluten to 'ripen' hence self-raising flours need to be weaker and to containless proteinous material than bread flours. Aprotein content of about 10% is sufficient. Theflour should contain not more than 14.5%moisture and preferably only 13.5%, as there isthen little fear of undue deterioration duringstorage. The use of sprouted native wheat in theblend is to be avoided, otherwise the flour willhave a high a-amylase acitivity. This may notprove detrimental when baked goods are made,but may well cause trouble with steamed or boiledgoods. The flour should be bright (colour grade

3.0 or less) and consequently in the past it used tobe bleached.Heat treated flourThe physical properties of wheat protein can bealtered by the application of heat, the effect of thetreatment lying in the direction of increasedstrength and stability and diminished extensibility.Properly applied heat, therefore, can lead to animprovement in the baking quality of flour milledfrom the wheat. The total effect of heat treatmentis dependent upon three factors, the temperature,the duration of the heating and the moisturecontent of the flour being heated. The higher themoisture content, the greater the effect of a givendegree of heating. A time and temperature ofheating which cause a beneficial change in theprotein quality of a flour containing 14% moisturemay completely ruin the baking quality of a flourcontaining 16% moisture.The heat treatment of flour can be used totallyor partially to eliminate its enzyme activity and todenature the gluten proteins. Such inactivatedflours are used for gravy thickening or soup man-ufacture, or as the basis of commercial battermixes.Malt flourMalt flour is produced by milling barley or wheatthat has been germinated and then kiln dried, a-Amylase is produced during the germination bu tthe final diastatic activity of the malt flour is influ-enced by the temperature to which the grain isexposed during kilning. Malt flour was used formany years as a corrective for low diastaticactivity in bread flour, a common rate of additionbeing 800 ppm. There is now a tendency for stan-dardized fungal a-amylase preparations to be usedin place of malt flour for this purpose, sincefungal amylase has a lower thermal death pointand will not continue to work in the baking oven,as was the case with malt flour. Malt flours ofmedium-to-high diastatic activity can be used inthe production of sticky malt breads of character-istic flavour. Heavy kilned or roasted malt flourscan have a bitter taste and are used mainly tocolour bread.BranThe object of the modern flour milling process isto split open the wheat grains and to scrape out


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the endosperm. A perfect separation is not pos-sible and some of the skins become powdered upin the flour, while some endosperm remainsattached to the residual skins. The co-product ofthe flour milling operation, which consists of sepa-rated skins plus adhering endosperm, is known asbran. Its dietary fibre content is in the region of40% (10% crude fibre). Bran is much used forstockfeeding but wheat bran fo r human consump-tion is used in brown breads and breakfast cereals,giving the consumer the benefits of increased fibrecontent in their diet.

GermThe commercially separated embryo of the wheatgrain is known as germ. Commercial germ is rela-tively high in protein content, fat and enzymeactivity. In Britain the proprietary germ breadsare made with commercial germ which has beensteam cooked.

Wbeatfeed and screenings

Wheatfeed is the name used for the by-products ofthe milling process other than germ. They com-prise bran, the coarse residue from the breakgrinds and fine wheatfeed, the accumulated resi-dues from the purifiers and the reduction grinding.The term 'screenings' is used to describe theusable impurities that are removed from wheatduring the cleaning processes and hence excludessuch contaminants as stones, string and pieces ofmetal. Screenings consist of cereals other thanwheat and foreign seeds and are ground andmixed into wheat feed. In Britain the screeningsremoved during cleaning of the wheat are gener-ally ground, and unless contaminated with ergot,added to the fine wheatfeed.

PolentasMaize polentas are coarse ground particles ofmaize corresponding to wheat semolina. The term'polenta' is also given to a porridge made fromthem.

Rice conesThese are granular rice particles with sizes resem-bling that of sand. They correspond to wheatsemolina.

Breakfast cereals(See Chapter 12)

Snack products(See Chapter 12)

SECONDARY PROCESSES

BREADMAKING

Bread is produced by making a dough from wheatflour and aerating this with carbon dioxide pro-duced by yeast fermentation. The proportion ofwater in the dough mixture varies with the type ofequipment used but is normally within the range55-65% of the flour w eight.About 2% SALT is added to give flavour to thebread. It has a depressant effect on the yeast an dthe addition of salt to the dough is often delayedto the 'knock-back' before dividing and mouldingin bulk fermented bread doughs. This is the so-called delayed salt method.The proportion of yeast required variesaccording to its activity and the proposed fermen-tation time. Various factors have been suggestedfor calculating the correct amount. Commonly itvaries between about 1% for bulk fermenteddoughs to 2% for short time doughs.Developments in the technology of breadmakinghave been concerned with speed and the elimina-tion of bulk fermentation and its concomitantweight loss due to flour being converted to carbondioxide by the yeast. About 80% of the breadeaten in the United Kingdom is made on plantbakeries.One of the most important developments inbreadmaking technology ha s been the Chorley-wood Bread Process (CBP), illustrated in Figure5.2, in which the dough is put into the ripe condi-tion, previously only obtained by long bulk fer-mentation, by the input of a large amount ofmechanical work within a short time. The methodhas been so successful that the bulk of the breadmanufactured in the UK is now made by thismethod.The characteristics of the CBP method are asfollows.(i) More yeast is used than in the bulk fermenta-tion method because of the much shortertotal fermentation time of about 1 h. Special


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Figure 5.2 Chorleywood bread process (reproducedfrom Gedye et al., 1981, with permission of the RoyalAgricultural Society of England).

yeast strains have been developed for thispurpose which are more active than thenormal continental yeasts,(ii) A very small percentage of fat is required(about 0.1%) with a melting point above thefinal dough temperature,(iii) Ascorbic acid is used as an oxidizingimprover,(iv) An extra 3-4% of water can be added to thedough,(v) The mechanical work input is 11 W h kg"1of dough during the 5 min mixing period.

The method was originally taken up by plantbakers but it is now used in one variation oranother by many small bakers. In the larger breadplants, doughs of 160-240 kg are mixed within 3

min. This requires very powerful mixers. In warmweather, because of the heat generated during themixing, the dough water is chilled before addition.The dough is divided straight from mixing, givena 5-10 min rest or intermediate proof, moulded,tinned, proved for typically 45 min and thenbaked.Activated dough development (ADD) is aquick alternative method of producing fermentedproducts, e.g. bread and rolls, without using bulkfermentation or mechanical dough development.The essential feature of the method is the use ofL-cysteine hydrochloride (at about 35 ppm offlour weight) as a reducing agent and ascorbicacid as an oxidizing improver. The addition of atleast 1% fat is regarded as essential to improvethe gas retention properties of the dough. Aswith the mechanical development of dough, extrayeast must be added to obtain the same degreeof final proof as obtained in the longer fermenta-tion methods. T he addition of L -cysteine hydro -chloride up to 75 ppm of flour is allowed in theUK.

Flour handlingThe flour is delivered in bulk to bakeries inbatches of up to 25 tonnes. It is then transferredpneumatically from the tanker to the flour silos,which commonly hold 50 tonnes each.

Dough mixingThe flour is drawn pneumatically from the silo tothe mixing station, where the amount requiredmay be called for by an automatic weigher, andthe correct amount of water at the correct tem-perature metered into the mixer. The other ingre-dients may be metered in or, more usually, addedby hand. A small proportion of doughs are stillmixed in the traditional steel open-bowl mixerwith one metal arm performing a kneading actionas the bowl rotates. The bulk of doughs, however,are mixed on high speed mixers requiring a sourceof chilled water to counteract the increase indough temperature caused by the rapid input ofenergy.It has long been known that the improvingaction of ascorbic acid requires its oxidation byatmospheric oxygen to dehydroascorbic acidbefore it becomes effective. It is also known thatduring mixing oxygen is rapidly removed from thedough by the yeast. Thus, it is perhaps not sur-prising that the addition of oxygen as the sole

Despatch

Wrapper/baggerSlicer

Cooler

DepannerDe-lidder

Oven

Final proverL id

TinSingle piece Four piece

Final moulder

Rest of first prover

Rounder/first moulder

Divider

Short rest

M ix into dough

Flour Other dry ingredients Yeast Water


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oxidant to the mixer during mechanical mixingwith ascorbic acid has a remarkable improvingeffect on the bread produced, comparable to theuse of ascorbic acid with potassium bromate. Thiseffect had been known for some time, but it wasonly in 1986 that the pressure to remove potas-sium bromate as an ingredient in bread resulted ina successful attempt to employ oxygen commer-cially.The previous fears of an explosion resultingfrom passing a gas containing 60% oxygen byvolume through the mixer headspace have no wbeen dispelled. In the presence of raw soya flour,which contains a lipoxidase, the method has anadded bleaching effect on the xanthins in theunbleached flour, producing a very bright whitecrumb.

Dough dividingDough dividers produce dough pieces of equalweight by a volumetric method. Ideally this shouldbe done by weighing, bu t this is only practical forthe small baker. Volumetric machines furnishdough pieces of constant weight only as long asthe density of the dough remains unchanged. Inpractice this is very difficult to achieve. It is there-fore essential that the weights of these doughpieces are checked frequently. Because of the diffi-culties associated with bread production and therequirements of the Weights and Measures Act, itis general practice to record the time and weightof each piece and to retain the records.

Handing-up (umbrella moulder)This is a machine fo r moulding dough pieces intoround shapes as they leave the divider. The bestknown type consists of a hemisperical shapedtunnel that spirals around a finely corrugatedcone. This cone revolves and in so doing carriesthe dough pieces through the tunnel and dis-charges them at the top in a nicely rounded con-dition. A stream of air blown over the cone helpsto prevent losses of pieces of dough due tosticking.

First proofIn order to relax the dough after dividing an dhanding-up, it is customary to allow the doughpieces to rest for a short period, usually 4-8 min.

Final moulderThe most common type of final moulder consistsof a vertical train of sets of rollers through whichthe round piece of dough drops, exiting onto amoving belt in the form of a pancake. The leadingedge of the pancake is flipped up and back bypassing it under a dragging chain curtain. Theresulting roll of dough passes under a pressureboard designed to push any entrapped air out ofthe ends of the roll. This roll is deposited into thegreased bread tin, either as a whole piece to givesingle piece bread, or cut into four pieces for theproduction of four piece bread.There has always been a desire to producebread with a bright white crumb and in large part,this is achieved by removing bran from the flourand bleaching the natural pigment remaining inthe endosperm. However, there is a residual dar-kening effect produced by the natural gas holes inthe slice, which is similar to that observed onlooking into an unlighted cave. In single piecebread, this effect is accentuated because the stan-dard method of moulding produces gas cells alongthe length of the loaf and these are cut acrosswhen the bread is sliced. Thus in cut bread onelooks down deep holes into relative darkness.In four pieced bread, the moulded doughpiece iscu t into four and the pieces laid in the tin side byside. In this way the gas holes are oriented acrossthe loaf, so that, when the loaf is cut, the cave-likeholes are cut along their length and theirmaximum depth is their width and not theirlength. They now act, not as dark holes, but asconcave reflecting surfaces with a consequentialapparent increase in the brightness of the crumbface.Final provingThe tinned dough pieces pass into a prover, wherethe tins are loaded onto travelling shelves so that,as they leave, a push bar can discharge a wholeshelf full of tins across the width of the travellingoven. The temperature and humidity of the proveratmosphere are controlled, 42 0C, 70-75% relativehumidity (RH) being typical. The internal tem-perature of the dough piece on leaving the proverafter 45-50 min is about 35 0C.BakingThe two main types of oven are the forced convec-tion ovens in which hot flue gases are circulatedaround the tins and the radiant ovens where hot


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flue gases pass through tubes which radiate heatto the tins. This latter kind of oven also has someforced turbulence to help distribute the heatevenly. Typical baking times vary between 23 and30 min. The bread leaving the oven is dislodgedfrom the tins by an air blast and sucked out anddeposited on the feed to the cooler.CoolingThe cooler is basically a tunnel through which thebread is passed against a countercurrent stream ofair of an adequate humidity to prevent too high aweight loss due to evaporation. Cooling is com-pleted in 2-3 h.

Cooling of baked goods between baking andpackaging requires an intermediate storage spaceand is a stage in processing during which there isa chance that the product will become contami-nated with mould spores. It is also a time duringwhich the collapse of some products occurs and inwhich the warm product is more susceptible todamage.Vacuum cooling offers the possibility ofavoiding these disadvantages. The hot bakedproduct enters a sealed chamber and is subjectedto a vacuum. The latent heat of evaporation, lostas some of the hot moisture within the productquickly evaporates, cools the product accordingly.It may then be rapidly moved onto the packagingline. One disadvantage of this method of coolingis the extra loss in weight incurred as a result ofthe evaporation of moisture and some allowancehas to be made for this in the formulation of theproduct.

SlicingThe cooled bread should have an internal tem-perature of 270C in order to avoid tearing duringslicing. Although band slicers do exist, in whichthe knife consists of a continuous band, the mostcommon kind of slicer used in the UK consists ofa reciprocating frame of scalloped-edged bladesthrough which the loaf is passed. The bread ispacked either in waxed paper or heat scalable filmor, more commonly, placed in plastic bags with aneck-tie.

BISCUIT MAKINGThe major ingredients of a biscuit dough are flour,sugar and fat. Compared with a bread dough,very little water is added and the doughs are very

firm. In mixing, the wheat gluten is not fullydeveloped and an extensible gluten is required fo rprocessing either in a rotary moulder or insheeting and cutting the biscuit shapes. Sodiummetabisulphite (up to 200 ppm of sulphur dioxideon flour weight) may be added to biscuit doughsto increase their extensibility. The cut biscuitshapes are baked rapidly in a hot oven to give adry product.

Continuous dough mixingDuring the 1960s a considerable amount of workwas carried out on developing a continuous mixerfor bread dough. Essentially, a continuous mixeris barrel shaped and consists of a primary mixingchamber, where the flour and solutions or aqueousdispersions of the other ingredients are mixed, fol-lowed by a 'work' chamber in which the dough issubjected to sufficient mechanical work to ripen it.The dough exiting from the mixer as a continuousribbon could then either be fed into conventionaldough dividers and through the usual bread plantor it could be divided at the mixer head anddropped straight into the baking tin. This methodgives a remarkable consistency of dough pieceweight, something which is difficult to attainotherwise.Continuous biscuit dough mixing is used verysuccessfully by the UK biscuit industry bu t contin-uous dough mixers have almost entirely disap-peared from the UK bread industry.

CAKE MAKINGThe basic ingredients of cakes are flour, short-ening, eggs, sugar and milk. However, the varietyof cakes that may be produced by varying the pro-portions of these ingredients and the types of flourand shortening, plus the addition of other ingredi-ents, is such that no attempt can be made to listthem here.A typical recipe is as follows:

Flour 1000 gButter 590 gShortening 90 gEggs 900 gSugar 700 gBaking powder 15 gCake batters are usually prepared by either thesugar batter or the flour batter method, theformer procedure, which is also known as thecreaming method, is preferable when high classcakes are being made, but the flour batter method


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is more suitable for the production of cheapercakes with a low egg content.

The sugar batter method is performed bycreaming together the fat and the sugar atmedium speed for about 10 min, adding the egg instages while mixing is continued, and finallymaking several alternate additions of flour andmilk. The egg should be brought to a temperatureof about 210C before being added to the mix orthe batter may curdle.

In the flour batter method, the shortening andthe flour are creamed together until a fluffy massis obtained. The eggs and sugar are whippedtogether and the resulting foam is them carefullyblended into the creamed fat and flour. Milk isthen added in small portions.

Cake batters are baked at temperatures between149 and 2080C depending upon their richness,their weight and their moisture content. Richerbatters of high sugar content require less heatthan those made on leaner formulae.

RUSK AND CRUMBMANUFACTURESausage rusk and crumb is baked from a tightchemically raised dough to give an open texturedbiscuit or bread which is ground into a coarsepale crumb, which has the ability to absorb largeamounts of water without becoming sticky.PASTA MAKING

eg g if yellow pasta is desired. The dough is eithersheeted or extruded into a range of strips, strandsor complicated shapes all known by Italiannames such as spaghetti, lasagne, vermicelli etc.The cut or extruded pasta shapes are dried slowlyin air to prevent the pasta from cracking. Figure5.3 illustrates a typical pasta manufacturingprocess.

GLUTEN AND STARCH SEPARATIONCoarsely ground flour is milled from wheat in asimple roller milling process. The flour is eithermixed into a dough or batter from which starchand fibre are washed to leave strands of glutenprotein. The gluten is agglomerated into lumps,dewatered and dried very carefully in a ring dryerto minimize any heat denaturation of the vitalwheat gluten. The starch is washed in hydrocy-clones or decanters before being sold either inslurry form or as a dried product. The process isillustrated in Figure 5.4.

SECONDARY PRODUCTSBAKED PRODUCTSBreadBread is a baked aerated dough, the primaryingredients of which are flour, salt and water. The

Figure 5.3 Pasta manufacture (reproduced from Gedye et al., 1981, with permission of the Royal Agricultural Societyof England).

Finished pasta product PackagingDrier

Pre-drier ExtruderDye

MixerPre-mixer

Storage

Semolina intake

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Food Industries Manual 007

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