8 Bread-baking Technology Principles of baking of discrete and separate particles, but the Primitive man, a nomadic hunter and gathe gluten is cohesive, forming a continuous three- erer of fruits and nuts started to settle down and dimensional structure which binds the four abandon his nomadic life when, in Neolithic particles together in dough. The gluten times he discovered how to sow the seeds of has peculiar extensible properties: it can be grasses and, in due time, reap a crop of 'cereal stretched like elastic, and possesses a degree grains. With this change in his way of life came of recoil or spring the beginnings of civilization which, in western air bubbles are folded into the dough. During Europe, is based on a diet relying on wheat, the subsequent handling of the dough these wheaten four, and the baked products made from bubbles divide or coalesce. Eventually the flour, the principal product being bread dough comes to resemble a foam, with the The function of baking is to present cereal bubbles trapped in the gluten network; fours in an attractive, palatable and digestible enzymes in the yeast start to ferment the sugars present in the flour and, later, the While wheat is the principal cereal used for sugars released by diastatic action of the breadmaking, other cereals, particularly rye, are amylases on damaged starch in the also used to some extent. The first part of this breaking them down to alcohol and chapter will consider breadmaking processes and dioxide. The carbon dioxide gas mixes with bread in which wheat four or meal is the sole the air in the bubbles and brings about expan cereal. The use of other cereals will be discussed ion of the dough. " Bread is fundamentally later(p. 211). foamed gluten"(Atkins, 1971) Three requirements in making bread from Use of milled wheat products for brea wheat flour are formation of a gluten network Bread is made by baking a dough which ha and the creation of air bubbles within it: the for its main ingredients wheaten flour, water incorporation of carbon dioxide to turn the gluten yeast and salt. Other ingredients which may be rheological properties of the gluten so that it added include fours of other cereals, fat malt flour, soya flour, yeast foods, emulsifiers, mill retains the carbon dioxide while allowing expan and milk products, fruit, gluten sion of the dough; and, finally, the coagulation of the material by heating it in the oven so that When these ingredients are mixed in correct the structure of the material is stabilized.The proportions, three processes commence advantage of having an aerated, finely vesiculated the protein in the four begins to hydrate, i. e. crumb in the baked product is that it is easily to combine with some of the water, to form masticated gluten(cf. pp. 70 and 174). Flour Corresponding with these requirements, there
8 Bread- ba ki ng Tech nology Principles of baking Primitive man, a nomadic hunter and gatherer of fruits and nuts, started to settle down and abandon his nomadic life when, in Neolithic times, he discovered how to sow the seeds of grasses and, in due time, reap a crop of ‘cereal grains’. With this change in his way of life came the beginnings of civilization which, in western Europe, is based on a diet relying on wheat, wheaten flour, and the baked products made from flour, the principal product being bread. The function of baking is to present cereal flours in an attractive, palatable and digestible form. While wheat is the principal cereal used for breadmaking, other cereals, particularly rye, are also used to some extent. The first part of this chapter will consider breadmaking processes and bread in which wheat flour or meal is the sole cereal. The use of other cereals will be discussed later (p. 211). Use of milled wheat products for bread Bread is made by baking a dough which has for its main ingredients wheaten flour, water, of discrete and separate particles, but the gluten is cohesive, forming a continuous threedimensional structure which binds the flour particles together in a ‘dough’. The gluten has peculiar extensible properties: it can be stretched like elastic, and possesses a degree of recoil or spring; - air bubbles are folded into the dough. During the subsequent handling of the dough these bubbles divide or coalesce. Eventually the dough comes to resemble a foam, with the bubbles trapped in the gluten network; - enzymes in the yeast start to ferment the sugars present in the flour and, later, the sugars released by diastatic action of the amylases on damaged starch in the flour, breaking them down to alcohol and carbon dioxide. The carbon dioxide gas mixes with the air in the bubbles and brings about expansion of the dough. “Bread is fundamentally foamed gluten” (Atkins, 1971). Three requirements in making bread from wheat flour are formation of a gluten network and the creation of air bubbles within it; the incorporation of carbon dioxide to turn the gluten network into a foam; and the development of the yeast and sa1t* Other ingredients which may be added inc1ude flours Of Other cerea1sY fat, ma1t rheological properties of the gluten so that it retains the carbon dioxide while allowing expan- flour, soya flour, yeast foods, emulsifiers, milk and milk products, fruit, gluten. When these ingredients are mixed in correct proportions, three processes commence: - the protein in the flour begins to hydrate, i.e. to combine with some of the water, to form gluten (cf. pp. 70 and 174). Flour consists sion of the dough; and, finally, the coagulation of the material by heating it in the oven so that the structure of the material is stabilized. The advantage of having an aerated, finely vesiculated crumb in the baked product is that it is easily masticated. Corresponding with these requirements, there 191
TECHNOLOGY OF CEREALS are three stages in the manufacture of bread than about 14% to permit safe storage, and xing and dough development, dough aeration satisfactory colour, and should meet specifica- and oven baking. The method of dough develop. tions regarding bleach and treatment ment and aeration that has been customary since pp.171-172) the time of the Pharaohs is panary fermentation by means of yeast These requirements are met by the type of heat called' trong’(cf.pp.81,92,174),ⅵiz wheat having a reasonably high protein content Ingredients Wherever possible, home-grown wheat is used for breadmaking, and this is the situation, for In the U. K, however, the home-grown wheat protein which is adequate in quantity and is, or until recently was, characteristically weak which, when hydrated, yields gluten which is viz, of low protein content, and would not, by satisfactory in respect of elasticity, strength itself, yield four from which bread, of the kind and stability to which u.K. consumers are accustomed. could satisfactory gassing properties: the levels of be made. It was therefore customary for flour amylase activity and of damaged starch (cf. millers in the U. K. to mill breadmaking flour pp. 183, 185) should be adequate to yield from a mixed grist of strong and weak wheats sufficient sugars, through diastatic action, to the strong wheat component being imported support the activity of the yeast enzymes generally from Canada, and the weak component during fermentation and proof; being home-grown U. K. wheat. Until the early satisfactory moisture content - not higher 1960s, the average breadmaking grist in the U. K Composition of bread wheat grist in U. K U.K %40 i other EC 讠b %%影 PIG& EC wereage compe ion of the bread wheat grist in the U. K. since 1973, in terms of U. K. wl n-EC wheat(data from MAFF, H-GCA, and NABIM
192 TECHNOLOGY OF CEREALS are three stages in the manufacture of bread: mixing and dough development, dough aeration, and oven baking. The method of dough development and aeration that has been customary since the time of the Pharaohs is panary fermentation by means of yeast. Ingredients Flour Good breadmaking flour is characterized as having: - protein which is adequate in quantity and which, when hydrated, yields gluten which is satisfactory in respect of elasticity, strength and stability; - satisfactory gassing properties: the levels of amylase activity and of damaged starch (cf. pp. 183, 185) should be adequate to yield sufficient sugars, through diastatic action, to support the activity of the yeast enzymes during fermentation and proof; - satisfactory moisture content - not higher than about 14% to permit safe storage, and satisfactory colour, and should meet specifications regarding bleach and treatment (cf. pp. 171-172). These requirements are met by the type of wheat called ‘strong’ (cf. pp. 81, 92, 174), viz. wheat having a reasonably high protein content. Wherever possible, home-grown wheat is used for breadmaking, and this is the situation, for example, in Canada and in the U.S.A., where such strong wheats, e.g. CWRS, HRS, are readily available. In the U.K., however, the home-grown wheat is, or until recently was, characteristically weak, viz. of low protein content, and would not, by itself, yield flour from which bread, of the kind to which U.K. consumers are accustomed, could be made. It was therefore customary for flour millers in the U.K. to mill breadmaking flour from a mixed grist of strong and weak wheats, the strong wheat component being imported, generally from Canada, and the weak component being home-grown U.K. wheat. Until the early 1960s, the average breadmaking grist in the U.K. Composition of bread wheat grist in U K 80 - 70 - YO 40- 10 - I A I I I I I I I 1w-i-r I I I I I I AAAAAAJ@@@@@@@@@% ~~~~~~~:L+-~ 9_gt+ EPJ\@-\@&lG&’+V\Pdd-\@&l9, ‘\ O Year FIG 8.1 Average composition of the bread wheat grist in the U.K. since 1973, in terms of U.K. wheat, other EC wheat, and non-EC wheat (data from MAFF, H-GCA, and NABIM)
BREAD-BAKING TECHNOLOG 193 would consist of 60-70% of imported strong wheat in the U. K. bread -wheat grist has fallen from plus 20-30% of weak home-grown wheat(with a about 70%in 1960 to about 15% in 1990(with a small proportion of filler'wheat of medium corresponding increase in the home-grown whea strength, cf. p. 87)-see Fig 8. 1, yielding a white proportion), with a considerable saving in the cost four of about 12% protein content of the raw material. By 1992, some millers were The imported Canadian wheat is more expen- supplying breadmaking four milled entirely from sive than the home-grown U. K. wheat and, in home-grown U. K. and ec wheats, with no non- consequence, there was a strong urge to decrease EC component, but with the addition of 2% or the ratio of strong to weak wheat. This change perhaps 2.5% of vital gluten was made possible in a number of ways, one of A similar reduction in the imported non-EC which was the advent of the CBP(cf. p. 203)(strong)wheat content of the breadmaking grist because, among other advantages, the cBp per- has also occurred in other countries mitted the use of a flour of about 1% lower protein One possible complication associated with the content to produce bread of quality equivalent to lowering of the strong/weak wheat ratio in the hat produced by the bFP(cf. p 201) bread grist is the reduced proportion of damaged Additional impetus to reduce still further the starch in the flour because of the frequent associa- proportion of imported strong wheat in the bread tion of strength with hardness(as in the importe grist followed the entry of the U. K into the EC, Canadian wheat)and, conversely, of weakness and the imposition of a heavy import levy, which with softness(as in the EC-grown wheats). It has run as high as f120-130 per tonne, on the desirable that the content of damaged starch cost of wheat imported from third (i.e. non-EC) should be maintained at a reasonably high level countries. Various measures have been adopted and this requirement can be met by adjustments whereby the proportion of home-grown (or EC- to the milling process (cf p. 149). However, it is grown) wheat in the breadmaking grist could be a fortunate coincidence that the two varieties of further increased, while maintaining loaf quality. wheat classified by breadmaking quality and They include: widely grown in the U. K. at the present time, breeding stronger wheats with higher yielding Avalon and mercia, both have a hard texture endosperm, and thus go some way towards potential for growing in the U.K. and other avoiding this complication EC countries. Examples of such promising new varieties are Avalon and Mercia. More- over the considerable increase in the size of the U. K. wheat harvest in recent years has Leavening provided the Aourmiller with the possibility Leavened baked goods are preferred in all of obtaining adequate supplies of these newer countries where wheat is available as a staple food varieties of good breadmaking quality Leavening can be achieved in several ways, awarding of remunerative premiums to growers including the following are poorer yielders than low protein wheats; I. Whisking egg into a foam with four and other of vital gluten as a bread ingredient(cf p.195 tion of sponge and other cakes supplementation of flours from lower-protein 2. Water vapour production as in Scandinavian home-grown wheats with air-classified high fat breads and puff pastry protein fractions of four(cf. p. 132); 3. Yeast use of high levels of fungal alpha-amylase(cf. 4. Baking powder p.196) Yeast and baking powder are the most import Figure 8. 1 shows that the proportion of imported ant. Each is appropriate for its own range of non-EC wheat(mostly Canadian CWRS wheat) products, and in some cases, such as doughnuts
BREAD-BAKING TECHNOLOGY 193 would consist of 60-70% of imported strong wheat in the U.K. bread-wheat grist has fallen from plus 20-30% of weak home-grown wheat (with a about 70% in 1960 to about 15% in 1990 (with a small proportion of ‘filler’ wheat of medium corresponding increase in the home-grown wheat strength, cf. p. 87) - see Fig. 8.1, yielding a white proportion), with a considerable saving in the cost flour of about 12% protein content. of the raw material. By 1992, some millers were The imported Canadian wheat is more expen- supplying breadmaking flour milled entirely from sive than the home-grown U.K. wheat and, in home-grown U.K. and EC wheats, with no nonconsequence, there was a strong urge to decrease EC component, but with the addition of 2% or the ratio of strong to weak wheat. This change perhaps 2.5% of vital gluten. was made possible in a number of ways, one of A similar reduction in the imported non-EC which was the advent of the CBP (cf. p. 203) (strong) wheat content of the breadmaking grist because, among other advantages, the CBP per- has also occurred in other countries. mitted the use of a flour of about 1% lower protein One possible complication associated with the content to produce bread of quality equivalent to lowering of the strong/weak wheat ratio in the that produced by the BFP (cf. p. 201). bread grist is the reduced proportion of damaged Additional impetus to reduce still further the starch in the flour because of the frequent associaproportion of imported strong wheat in the bread tion of strength with hardness (as in the imported grist followed the entry of the U.K. into the EC, Canadian wheat) and, conversely, of weakness and the imposition of a heavy import levy, which with softness (as in the EC-grown wheats). It is has run as high as &120-130 per tonne, on the desirable that the content of damaged starch cost of wheat imported from third (Le. non-EC) should be maintained at a reasonably high level, countries. Various measures have been adopted and this requirement can be met by adjustments whereby the proportion of home-grown (or EC- to the milling process (cf. p. 149). However, it is grown) wheat in the breadmaking grist could be a fortunate coincidence that the two varieties of further increased, while maintaining loaf quality. wheat classified by breadmaking quality and They include: widely grown in the U.K. at the present time, Avalon and Mercia, both have a hard textured - breeding stronger wheats with higher yielding endosperm, and thus go some way towards potential for growing in the U.K. and other avoiding this complication. EC countries. Examples of such promising new varieties are Avalon and Mercia. Moreover, the considerable increase in the size of Leavening the U.R. wheat harvest in recent years has provided the flourmiller with the possibility Leavened baked goods are preferred in all of obtaining adequate supplies of these newer countries where wheat is available as a staple food. varieties of good breadmaking quality; Leavening can be achieved in several ways, - awarding of remunerative premiums to growers including the following: for higher protein home-grown wheats which are poorer yielders than low protein wheats; - use of vital gluten as a bread ingredient (cf. p. 195); - supplementation of flours from lower-protein home-grown wheats with air-classified high protein fractions of flour (cf. p. 132); - use of high levels of fungal alpha-amylase (cf. p. 196). Figure 8.1 shows that the proportion of imported non-EC wheat (mostly Canadian CWRS wheat) 1. Whisking egg into a foam with flour and other ingredients. This method is used in production of sponge and other cakes. 2. Water vapour production as in Scandinavian flat breads and puff pastry. 3. Yeast. 4. Baking Powder. Yeast and baking powder are the most important. Each is appropriate for its own range of products, and in some cases, such as doughnuts
194 TECHNOLOGY OF CEREALS coffee cake, and pizza-dough, either may be used of one strain to the genome of another. Strains alone or in combination that have an excellent performance in sugar-rich doughs normally show a poor performance in Baking powders lean doughs, but the subject of a European Patent EP0 306 107 A2) is a yeast that performs well Baking powders depend upon sodium bicarbon- both in high sucrose conditions and also in ' lean ate as a source of co z gas, which may be liberated conditions, where maltose is the available sub- by the action of sodium acid phosphate, mono- strate. The technique involved was the introduc- calcium phosphate, sodium aluminium phos- tion of genes coding for increased activity of the phate or glucono-8-lactone. One hundred grams two enzymes maltose permease and maltase(alpha- f baking powder generates 15 mg (or 340 mM, glucosidase), allowing best use to be made of the or 8.2 D of COz. Some is released at dough limited quantities of maltose available in a lean temperature and the remainder during baking Ability to ferment sugars anaerobically remains Yeast the major criterion of selection, but meeting this under different conditions has led to the introduc The quantity of yeast used is related inversely tion of specialized strains. The conditions that to the duration of fermentation, longer fermenta- provide the challenge include the requirements tion systems generally employing somewhat lower (a) to be supplied and stored in a dry form with levels of yeast and also lower dough temperatures. a longer life than the traditional compressed form Thus, 1% of yeast on four wt would be used for (b)to retain high activity in high sugar formula- a 3 h straight dough system with the dough at tions and (c) to retain activity in yeast-leavened 27C, whereas 2-3%of yeast on flour wt would be frozen doughs required for a no-time dough at 27-30.C. Yeast activity increases rapidly with temperature, and its level of use is therefore reduced if the temper Dried yeasts ature is increased within a fixed tir Until the early 1970s, two strains of Saccharo- In addition to providing CO2 as a leavening myces cerivisiae were used widely. The yeast was agent, yeast also affects rheological properties of grown to a nitrogen level of 8 2-8.8%(on a dry dough through the lowering of ph by CO2 basis), and an A DY.(active dry yeast), which ical effects of bubble expansion. Further, yeast in the pelleted product, it had only 75-80% of ontributes significantly to the flavour and aroma the gassing activity of the compressed yeasts of baked products (when compared on the same m.c. basis). New Yeast is used in several different forms: com- products available since that time have allowed pressed, cream (liquid), dried into pellets, and the gap to be narrowed, although it does still exist instant active powders Three forms of dried yeast are now available In recent years, attitudes to yeast production A D.Y., and the pot have become more enterprizing Specialized strains A D.Y. (I.A. D P powdered products Instant and protected A.D.Y. have been selected and bred to meet newly identi- (P.A. .Y fied criteria. This has resulted partly from changing A D.Y. must be rehydrated in warm water technologies within the baking industries and (35%-40oC)before it is added to dough, while partly from new means of genetic manipulation. I A D.Y. and P A D.Y. can be added to dry Examples of these innovations are the replace- ingredients before mixing. In fact, this results in ment of conventional spore fusion by protoplast more productive gassing. During storage, dried fusion, and genetic engineering through the use yeasts are subject to loss of activity in oxygen of recombinant DNA(rDNA)for introduction The improved strains are supplied in vacuum of an advantageous segment of the genetic materials packs or in packs with inert gas in the headspace
194 TECHNOLOGY OF CEREALS coffee cake, and pizza-dough, either may be used of one strain to the genome of another. Strains alone or in combination. that have an excellent performance in sugar-rich doughs normally show a poor performance in lean doughs, but the subject of a European Patent (El' 0 306 107 A2) is a yeast that performs well Baking powders Baking powders depend upon sodium bicarbon- both in high sucrose conditions and also in 'lean' ate as a source of C02 gas, which may be liberated conditions, where maltose is the available subby the action of sodium acid phosphate, mono- strate. The technique involved was the introduccalcium phosphate, sodium aluminium phos- tion of genes coding for increased activity of the phate or glucono-&lactone. One hundred grams two enzymes maltose permease and maltase (alphaof baking powder generates 15 mg (or 340 mM, glucosidase), allowing best use to be made of the or 8.2 1) of C02. Some is released at dough limited quantities of maltose available in a lean temperature and the remainder during baking. dough. Ability to ferment sugars anaerobically remains the major criterion of selection, but meeting this under different conditions has led to the introduc- Yeast The quantity of yeast used is related inversely tion of specialized strains. The conditions that to the duration of fermentation, longer fermenta- provide the challenge include the requirements: tion systems generally employing somewhat lower (a) to be supplied and stored in a dry form with levels of yeast and also lower dough temperatures. a longer life than the traditional compressed form; Thus, 1% of yeast on flour wt would be used for (b) to retain high activity in high sugar formulaa 3 h straight dough system with the dough at tions and (c) to retain activity in yeast-leavened 27"C, whereas 2-3% of yeast on flour wt would be frozen doughs. required for a no-time dough at 27"-3OoC. Yeast Dried yeasts activity increases rapidly with temperature, and its level of use is therefore reduced if the temperature is increased within a fixed time process. Until the early 1970s, two strains of SaccharoIn addition to providing C02 as a leavening myces cerivisiae were used widely. The yeast was agent, yeast also affects rheological properties of grown to a nitrogen level of 8.2-8.8% (on a dry dough through the lowering of pH by C02 basis), and an A.D.Y. (active dry yeast), which production, evolution of alcohol, and the mechan- was grown to a nitrogen content of 7.0%. Thus, ical effects of bubble expansion. Further, yeast in the pelleted product, it had only 75-80% of contributes significantly to the flavour and aroma the gassing activity of the compressed yeasts of baked products. (when compared on the same m.c. basis). New Yeast is used in several different forms: com- products available since that time have allowed pressed, cream (liquid), dried into pellets, and the gap to be narrowed, although it does still exist. instant active powders. Three forms of dried yeast are now available: In recent years, attitudes to yeast production A.D.Y., and the powdered products Instant have become more enterprizing. Specialized strains A.D.Y. (I.A.D.Y.) and protected A.D.Y. have been selected and bred to meet newly identi- (P.A.D.Y.). fied criteria. This has resulted partly from changing A.D.Y. must be rehydrated in warm water technologies within the baking industries and (35"40"C) before it is added to dough, while partly from new means of genetic manipulation. I.A.D.Y. and P.A.D.Y. can be added to dry Examples of these innovations are the replace- ingredients before mixing. In fact, this results in ment of conventional spore fusion by protoplast more productive gassing. During storage, dried fusion, and genetic engineering through the use yeasts are subject to loss of activity in oxygen. of recombinant DNA (rDNA) for introduction The improved strains are supplied in vacuum of an advantageous segment of the genetic materials packs or in packs with inert gas in the headspace
BREAD-BAKING TECHNOLOGY (I A D.Y., or in the presence of an antioxi the bread soft and palatable for a longer period (P.A. D.Y. .PA D.Y. features in complete which is equivalent to an anti-staling effect containing flour and other ingredients but the (Hoseney, 1986) four present must be at a very low m c to avoid During storage of flour, free fatty acids accumu- moisture transfer and reduction in the level of late owing to the breakdown of the natural fats production against oxidation and the gluten formed from the protein becomes less soluble and shorter in character. When flour High sugar yeast that has been stored for a long time, e. g. a year, at ambient temperature is used for the CBP, the Products such as Danish pastries, doughnuts fat level should be increased to about 1.5%on nd sweet buns have a high sugar content. The flour wt high osmotic pressures involved are not tolerated by standard yeast strains, but good strains are available as I.A. D.Y. products. Japanese com- Sugar pressed yeasts can also withstand high osmotic Sugar is generally added to bread made in the conditions U.S.A. giving an acceptable sweet favour, but Frozen dough yeasts However, sugar may be included in prover mixes The production of breads from frozen doughs at the point of sale, has increased dramatically Vital gluten and has created a requirement for cryoresistant Vital wheat gluten, viz. gluten prepared in such yeasts. Most yeasts withstand freezing, but way that it retains its ability to absorb water deteriorate rapidly during frozen storage The and form a cohesive mass (cf pp 70, 174), is now best cryoresistant strains perform well in sweet widely used in the U. K. and in other EC countries goods but less well in lean doughs. The require- as an ingredient of bread ment has not been fully satisfied (Reed and Nagodawithana, 1991) at levels of 0.5-3. 0% on flour wt to improve the texture and raise the protein content of bread, crispbread, and speciality breads such as vienna bread and hamburger rolls Salt is added to develop favour. It also toughe to fortify weak flours, and to permit the use ens ne gluten and gives a less sticky dough Salt slows by millers of a wheat grist of lower strong/ down the rate of fermentation and its addition is weak wheat ratio (particularly in the eC sometimes delayed until the dough has been countries) by raising the protein content of partly fermented The quantity used is usually the flour(cf p. 193); 1.8-2. 1%on flour wt, giving a concentration of in starch-reduced high protein breads(cf. p 1.1-1. 4% of salt in the bread. salt is added either 209), in which the gluten acts both as a source as an aqueous solution(brine)or as the dry solid of protein and as a texturing agent in high-fibre breads(cf. p. 209)now being made in the u.s.A. to maintain the texture Fat is an essential ingredient for no-time In the U.S. A about 70%of all vital gluten is doughs, such as the CBP. Added at the rate of used for bread, rolls, buns and yeast-raised goods about 1% on four wt, fat improves loaf volume, (Magnuson, 1985). vital gluten is also used as a reduces crust toughness and gives thinner crumb binder to raise the protein level in meat products cell walls, resulting in a softer-textured loaf with e.g. sausages, and in breakfast cereals(e.g improved slicing characteristics. Fat also keeps Kelloggs Special K), breadings, batter mixes
BREAD-BAKING TECHNOLOGY 195 (I.A.D.Y.), or in the presence of an antioxidant the bread soft and palatable for a longer period, (P.A.D.Y.). P.A.D.Y. features in complete mixes which is equivalent to an anti-staling effect containing flour and other ingredients but the (Hoseney, 1986). flour present must be at a very low m.c. to avoid During storage of flour, free fatty acids accumumoisture transfer and reduction in the level of late owing to the breakdown of the natural fats, production against oxidation. and the gluten formed from the protein becomes less soluble and shorter in character. When flour that has been stored for a long time, e.g. a year, High sugar yeast at ambient temperature is used for the CBP, the Products such as Danish pastries, doughnuts fat level should be increased to about 1.5% on and sweet buns have a high sugar content. The flour wt. high osmotic pressures involved are not tolerated by standard yeast strains, but good strains are Sugar available as I.A.D.Y. products. Japanese compressed yeasts can also withstand high osmotic Sugar is generally added to bread made in the conditions. U.S.A., giving an acceptable sweet flavour, but it is not usually added to bread in the U.K. However, sugar may be included in prover mixes. Frozen dough yeasts The production of breads from frozen doughs, vital gluten at the point of sale, has increased dramatically and has created a requirement for cryoresistant Vital wheat gluten, viz. gluten prepared in such yeasts. Most yeasts withstand freezing, but a way that it retains its ability to absorb water deteriorate rapidly during frozen storage. The and form a cohesive mass (cf. pp. 70,174), is now best cryoresistant strains perform well in sweet widely used in the U.K. and in other EC countries goods but less well in lean doughs. The require- as an ingredient of bread: - at levels of 0.5-3.0% on flour wt to improve ment has not been fully satisfied (Reed and the texture and raise the protein content of Nagodawithana, 199 1). bread, crispbread, and speciality breads such Salt as Vienna bread and hamburger rolls; - to fortify weak flours, and to permit the use by millers of a wheat grist of lower strong/ Salt is added to develop flavour. It also toughens the gluten and gives a less sticky dough. Salt slows weak wheat ratio (particularly in the EC down the rate of fermentation, and its addition is countries) by raising the protein content of the flour (cf. p. 193); sometimes delayed until the dough has been partly fermented. The quantity used is usually - in starch-reduced high protein breads (cf. p. 209), in which the gluten acts both as a source 1.8-2.1% on flour wt, giving a concentration of of protein and as a texturing agent; 1.1-1.4% of salt in the bread. Salt is added either - in high-fibre breads (cf. p. 209) now being as an aqueous solution (brine) or as the dry solid. made in the U.S.A., to maintain the texture Fat and volume. Fat is an essential ingredient for no-time In the U.S.A., about 70% of all vital gluten is doughs, such as the CBP. Added at the rate of used for bread, rolls, buns and yeast-raised goods about 1% on flour wt, fat improves loaf volume, (Magnuson, 1985). Vital gluten is also used as a reduces crust toughness and gives thinner crumb binder to raise the protein level in meat products, cell walls, resulting in a softer-textured loaf with e.g. sausages, and in breakfast cereals (e.g. improved slicing characteristics. Fat also keeps Kelloggs Special K), breadings, batter mixes
TECHNOLOGY OF CEREALS pasta foods, pet foods, dietary foods and textured permit the use of four of up to 2% lower protein getables products(t v.p. content with no loss in loaf quality The origin of the gluten is of little importance A similar increase in loaf volume could be when used to raise the flour protein content by produced by addition of a variety of commercial only 1-2%: thus, U.K. -grown wheat can be used carbohydrase enzyme preparations(Cauvain and to provide vital gluten, thereby further reducing Chamberlain, 1988) the dependence on imported strong wheat. The vital gluten is generally added to the flour at the mill, particularly in the case of wholemeal Soya flour (McDermott, 1985). Enzyme-active soya flour is widely a bread additive at a level of about 0.7% on Gluten flou four wt. Advantages claimed for its use include beneficial oxidizing effect on the flour, bleaching This is a blend of vital wheat gluten with wheat effect on flour pigments( B-4 carotene due lour, standardized to 40% protein content in the presence of lipoxygenase, increase in loaf volume, U.S.A improvement in crumb firmness and crust appear- ance, and extension of shelf life(Anon, 1988a) Fungal amylase (cf.p.215) The improving action and bleaching propert Besides the use of low levels(e. g 7-10 Farrand of enzyme-active soya flour are due to peroxy Units)of fungal amylase to correct a deficiency radicals that are released by a type-2 lipoxygenase in natural cereal alpha-amylase and improve gas- which has an optimum activity at ph 6. 5. Enzyme- sing(cf p. 198), fungal amylase, sold under such active soya flour has two effects in a flour dough trade names as myl.x and amylzyme, has a it increases mixing tolerance, and it improves marked effect in increasing loaf volume when used dough rheology, viz. by decreasing extensibility at much higher levels as a bread ingredient in rapid and increasing resistance to extension. The action eadmaking systems. Use of high levels is possible of the lipoxygenase is to oxidize the linoleic acid cause the fungal amylase has a relatively low in the lipid fraction of the wheat four, but the thermal inactivation temperature. The fungal action only occurs in the presence of oxygen amylase starts to act during the mixing stage,( Grosch, 1986) when it causes a softening of the dough, which must be corrected by reducing the amount of doughing water, so as to maintain the correct Improving agents dough consistency. Use of high levels of fungal The use and effects of improving agents amylase in the BFP would not be desirable, as potassium bromate, ascorbic acid, azodicarbon the dough softening effect would be too severe. amide, L-cysteine have been discussed in Hence, addition of fungal amylase at these high Ch. 7 levels is made by the baker, and not at the mill the early part of the baking process, attacking Physical treatments gelatinized starch granules, improving gas reten The breadmaking quality of flour can be tion, and helping the dough to maintain a fuid improved also by physical means, e.g. by controlled condition, thus prolonging the dough expansion heat treatment (cf. p. 113) or by an aeration time and increasing loaf volume The increase in process, in which four is whipped with water at loaf volume is directly related to the level of fungal high speed for a few minutes and the batter then amylase addition up to about 200 Farrand Units. mixed with dry flour Improvement is brought The effect of the addition of about 120 farrand about by oxidation with oxygen in the air, prob Units of fungal amylase is so powerful that it may ably assisted by the lipoxidase enzymes (cf
196 TECHNOLOGY OF CEREALS pasta foods, pet foods, dietary foods and textured permit the use of flour of up to 2% lower protein vegetables products (t .v. p. ) . content with no loss in loaf quality. The origin of the gluten is of little importance A similar increase in loaf volume could be when used to raise the flour protein content by produced by addition of a variety of commercial only 1-2%: thus, U.K.-grown wheat can be used carbohydrase enzyme preparations (Cauvain and to provide vital gluten, thereby further reducing Chamberlain, 1988). the dependence on imported strong wheat. The Soya flour vital gluten is generally added to the flour at the mill, particularly in the case of wholemeal. (McDermott, 1985). Enzyme-active soya flour is widely used as a bread additive, at a level of about 0.7% on flour wt. Advantages claimed for its use include: beneficial oxidizing effect on the flour, bleaching Gluten flour This is a blend of vital wheat gluten with wheat effect on flour pigments @-carotene) due to the flour, standardized to 40% protein content in the presence of lipoxygenase, increase in loaf volume, U.S.A. improvement in crumb firmness and crust appearance, and extension of shelf life (Anon., 1988a) (cf. p. 215) The improving action and bleaching properties Fungal amylase Besides the use of low levels (e.g. 7-10 Farrand of enzyme-active soya flour are due to peroxy Units) of fungal amylase to correct a deficiency radicals that are released by a type-2 lipoxygenase, in natural cereal alpha-amylase and improve gas- which has an optimum activity at pH 6.5. Enzymesing (cf. p. 198), fungal amylase, sold under such active soya flour has two effects in a flour dough: trade names as MYL-X and Amylozyme, has a it increases mixing tolerance, and it improves marked effect in increasing loaf volume when used dough rheology, viz. by decreasing extensibility at much higher levels as a bread ingredient in rapid and increasing resistance to extension. The action breadmaking systems. Use of high levels is possible of the lipoxygenase is to oxidize the linoleic acid because the fungal amylase has a relatively low in the lipid fraction of the wheat flour, but the thermal inactivation temperature. The fungal action only occurs in the presence of oxygen amylase starts to act during the mixing stage, (Grosch, 1986). when it causes a softening of the dough, which must be corrected by reducing the amount of Improving agents doughing water, so as to maintain the correct dough consistency. Use of high levels of fungal The use and effects of improving agents - amylase in the BFP would not be desirable, as potassium bromate, ascorbic acid, azodicarbonthe dough softening effect would be too severe. amide, L-cysteine - have been discussed in Hence, addition of fungal amylase at these high Ch. 7. levels is made by the baker, and not at the mill. Physical treatments The fungal amylase continues to act during the early part of the baking process, attacking gelatinized starch granules, improving gas reten- The breadmaking quality of flour can be tion, and helping the dough to maintain a fluid improved also by physical means, e.g. by controlled condition, thus prolonging the dough expansion heat treatment (cf. p. 113) or by an aeration time and increasing loaf volume. The increase in process, in which flour is whipped with water at loaf volume is directly related to the level of fungal high speed for a few minutes and the batter then amylase addition up to about 200 Farrand Units. mixed with dry flour. Improvement is brought The effect of the addition of about 120 Farrand about by oxidation with oxygen in the air, probUnits of fungal amylase is so powerful that it may ably assisted by the lipoxidase enzymes (cf
READ-BAKING TECHNOLOGY 197 p. 68) present in the flour. A similar improving protein)in the grist- which is uneconomic, the effect can be obtained by overmixing normal most convenient way of increasing water absorp- dough(without the batter stage ) cf. the Chorley- tion is to increase the degree of starch damage wood Bread Process(p. 203) The miller can bring this about by modifying the milling conditions(cf. p. 149) Doughmaking Water absorption The enzymes principally concerned in panary The amount of water to be mixed with four fermentation are those that act upon carbohydrates to make a dough of standard consistency is usually alpha-amylase and beta-amylase in flour, and 55-61 pt per 100 pt of four, increasing in maltase, invertase and the zymase complex in yeast proportion to the contents of protein and damaged Zymase is the name that was formerly used for starch(cf. pp 62, 174)in the flour. about fourteen enzymes Flour contains protein, undamaged starch The starch of the four is broken down to the nules and damaged starch granules, all of disaccharide maltose by the amylase enzymes; the which absorb water, but to differing degrees. maltose is split to glucose(dextrose)by maltase; Farrand( 1964) showed that the uptake of water, glucose and fructose are fermented to carbon per gram of component, was 2.0 g for protein, dioxide and alcohol by the zymase complex damaged starch. Thus, flours from strong wheat mechanically damaged during milling(cf ppe g 0-0.3 g for undamaged starch, and Some of the starch granules in four becom (with higher protein content) and from hard 149, 185),and only these damaged granules can wheat(with a higher damaged starch content) be attacked by the flour amylases. It is therefore require more water than is needed by flours from essential that the flour should contain adequate weak(lower protein)or soft(less damaged starch) damaged starch to supply sugar during fermenta- wheats to make a dough of standard consistency. tion and proof. When the amylase enzymes break Besides the protein and starch, the soluble part down the damaged starch, water bound by the of the hemicellulose(pentosan) forming the walls starch is released and causes softening of the of the endosperm cells also absorbs water. dough. This situation must be borne in mind The water used in dough-making should have when calculating the amount of doughing water the correct temperature so that, taking account required, the amount of water released being ar temperature dependent not only on the level of damaged temperature rise during mixing, the dough is starch, but also on the alpha-amylase activity made to the correct final temperature. When length of fermentation time, and dough tempera using a process such as the CBP(cf. p 203)in ture. Excessive levels of starch damage, however which the temperature rise during mixing may have an adverse effect on the quality of the bread be as much as 14C, it may be necessary to cool (cf. p. 150): loaf volume is decreased, and the the doughing water. bread is less attractive in appearance It is important, particularly in plant bakeries, There are small quantities of sugar naturally to maintain constant dough consistency. This present in four(cf p. 55)but these are soon used may be done by adjusting the level of water up by the yeast, which then depends on the sugar addition automatically or semi-automatically. produced by diastatic action from the starch Determination of water absorption of the flour by During fermentation about 0. 8 kg of alcohol is means of the Brabender Farinograph is described produced per 100 kg of flour, but much of it is driven off during the baking process. New bread A four with high water absorption capacity is is said to contain about 0. 3% of alcohol. Secondary generally preferred for breadmaking. Apart from products, e.g. acids, carbonyls and esters, may ncreasing the proportion of strong wheat(high affect the gluten or impart flavour to the bread
BREAD-BAKING TECH NO LOGY 197 p. 68) present in the flour. A similar improving protein) in the grist - which is uneconomic, the effect can be obtained by overmixing normal most convenient way of increasing water absorpdough (without the batter stage): cf. the Chorley- tion is to increase the degree of starch damage. wood Bread Process (p. 203). The miller can bring this about by modifying the milling conditions (cf. p. 149). Doughmaking Fermentation The enzymes principally concerned in panary Water absorption The amount of water to be mixed with flour fermentation are those that act upon carbohydrates: to make a dough of standard consistency is usually alpha-amylase and beta-amylase in flour, and 55-61 pt per 100 pt of flour, increasing in maltase, invertase and the zymase complex in yeast. proportion to the contents of protein and damaged Zymase is the name that was formerly used for starch (cf. pp. 62, 174) in the flour. about fourteen enzymes. Flour contains protein, undamaged starch The starch of the flour is broken down to the granules and damaged starch granules, all of disaccharide maltose by the amylase enzymes; the which absorb water, but to differing degrees. maltose is split to glucose (dextrose) by maltase; Farrand (1964) showed that the uptake of water, glucose and fructose are fermented to carbon per gram of component, was 2.0 g for protein, dioxide and alcohol by the zymase complex. 0-0.3 g for undamaged starch, and 1.0 g for Some of the starch granules in flour become damaged starch. Thus, flours from strong wheat mechanically damaged during milling (cf. pp. 62, (with higher protein content) and from hard 149, 185), and only these damaged granules can wheat (with a higher damaged starch content) be attacked by the flour amylases. It is therefore require more water than is needed by flours from essential that the flour should contain adequate weak (lower protein) or soft (less damaged starch) damaged starch to supply sugar during fermentawheats to make a dough of standard consistency. tion and proof. When the amylase enzymes break Besides the protein and starch, the soluble part down the damaged starch, water bound by the of the hemicellulose (pentosan) forming the walls starch is released and causes softening of the of the endosperm cells also absorbs water. dough. This situation must be borne in mind The water used in dough-making should have when calculating the amount of doughing water the correct temperature so that, taking account required, the amount of water released being of the flour temperature and allowing for any dependent not only on the level of damaged temperature rise during mixing, the dough is starch, but also on the alpha-amylase activity, made to the correct final temperature. When length of fermentation time, and dough temperausing a process such as the CBP (cf. p. 203) in ture. Excessive levels of starch damage, however, which the temperature rise during mixing may have an adverse effect on the quality of the bread be as much as 14"C, it may be necessary to cool (cf. p. 150): loaf volume is decreased, and the the doughing water. bread is less attractive in appearance. It is important, particularly in plant bakeries, There are small quantities of sugar naturally to maintain constant dough consistency. This present in flour (cf. p. 55) but these are soon used may be done by adjusting the level of water up by the yeast, which then depends on the sugar addition automatically or semi-automatically. produced by diastatic action from the starch. Determination of water absorption of the flour by During fermentation about 0.8 kg of alcohol is means of the Brabender Farinograph is described produced per 100 kg of flour, but much of it is on p. 186. driven off during the baking process. New bread A flour with high water absorption capacity is is said to contain about 0.3% of alcohol. Secondary generally preferred for breadmaking. Apart from products, e.g. acids, carbonyls and esters, may increasing the proportion of strong wheat (high affect the gluten or impart flavour to the bread
TECHNOLOGY OF CEREALS rom Aspergillus oryzae or A. awamori, to the flour Both alpha- and beta-amylases catalyze the (cf. p. 196). Fungal amylase is preferred to malt flour because the thermal inactivation temperature hydrolysis of starch, but in different ways(cf p. of fungal amylase is lower (75.C) than that of 67) Normal four from sound wheat alpha-amylase. The amount of alpha-amylase, the consequent difficulties in slicing bread with however,increases considerably when wheat a sticky crumb Gas retention is a property of the flour protein germinates. Indeed, flour from wheat containing the gluten, while being sufficiently extensible to many sprouted grains may have too high an alpha- allow the loaf to rise, must yet be strong enough to prevent gas escaping too readily, as this would nB, some of the starch is changed into dextrin-like lead to collapse of the loaf. The interaction of he crumb is weakened, and the dextrins make the crumb sticky(cf. p 67). However, flour with too powerful effect on gas retention high a natural alpha-amylase activity could be used for making satisfactory bread by microwave Dough development or radio-frequency baking methods(cf. p. 206) Another possibility would be to make use of an Protein alpha-amylase inhibitor, e.g. one prepared from The process of dough development, which barley, as described in Canadian Patent No 1206157 of 1987(Zawistowska et al. 1988). occurs during dough ripening, concerns the The functions of starch in the baking of bread hydrated protein component of the flour. It are to dilute the gluten to a desirable consistenc involves an uncoiling of the protein molecules to provide sugar through diastasis, to provide a and their joining together, by cross-linking, to strong union with gluten, and by gelatinization form a vast network of protein which is collec- to become flexible and to take water from the tively called gluten. The coils of the protein gluten, a process which helps the gluten film to molecules are held together by various types of et and become rigid bonds, including disulphide(Ss-) bonds, and it is the severing of these bonds -allowing the molecule to uncoil- and their rejoining in Gas production and gas retention different positions linking separate protein molecules together that constitutes a major The creation of bubble structure in the dough part of dough development is a fundamental requirement in breadmaking Sulphydryl (SH) groups(cf. pp 66, 174)are The carbon dioxide generated by yeast activity also present in the protein molecules as side groups does not create bubbles: it can only inflate gas of the amino acid cysteine. Reaction between the cells already formed by the incorporation of air -SH groups and the-SS-bonds permits new inter- during mixing and intra-protein/polypeptide relationships to be equate gas must be produced during fermen- formed via-Ss-bonding, one effect of this inter- tation, otherwise the loaf will not be inflated suf- change being the relaxation of dough by the relief ficiently Gas production depends on the quantity of stress induced by the mixing process of soluble sugars in the flour, and on its diastatic While gluten is important in creating an extens- power. Inadequate gassing (maltose value less ible framework, soluble proteins in the dough than 1.5) may be due to an insufficiency of liquor may also contribute to gas retention by damaged starch or to a lack of alpha-amylase; the forming an impervious lining layer within cells latter can be corrected by adding sprouted wheat effectively blocking pin- holes in cell walls( Gar to the grist, or malt four, or fungal amylase, e.g. et al., 1990)
198 TECHNOLOGY OF CEREALS Amylase from Aspergillus oryzae or A. awamori, to the flour (cf. p. 196). Fungal amylase is preferred to malt flour because the thermal inactivation temperature cereal alpha-amylase (87"C), and its use avoids the the consequent difficulties in slicing bread with a sticky crumb. Gas retention is a property of the flour protein: the gluten, while being sufficiently extensible to to prevent gas escaping too readily, as this would lead to collapse of the loaf. The interaction of added fat with flour components also has a powerful effect on gas retention. Dough development Protein The process of dough development, which occurs during dough ripening, cOncernS the hydrated protein component of the flour. It involves an uncoiling of the protein molecules and their joining together, by cross-linking, to form a vast network of protein which is collectively called gluten. The coils of the protein molecules are held together by various types of it is the severing of these bonds - allowing the molecule to uncoil - and their rejoining in different positions - linking separate protein molecules together - that constitutes a major part of dough development. Sulphydryl (-SH) groups (cf. pp. 66, 174) are also present in the protein molecules as side groups of the amino acid cysteine. Reaction between the -SH groups and the -SS- bonds permits new interand intra-proteidpolypeptide relationships to be formed via -SS- bonding, one effect of this interchange being the relaxation of dough by the relief of stress induced by the mixing process. While gluten is important in creating an extensible framework, soluble proteins in the dough liquor may also contribute to gas retention by forming an impervious lining layer within cells, effectively blocking pin-holes in cell walls (Gan et al., 1990). Both alpha- and beta-amylases catalyze the hydro1ysis Of starch, but in different ways (cf' P' of fungal amylase is lower (75°C) than that of 67). beta-amylase but generally only a small amount of alpha-amylase. The amount of alpha-amylase, however, increases considerably when wheat germinates. Indeed, flour from wheat containing amylase activity, with the result that, during baking, some of the starch is changed into dextrin-like substances. Water-holding capacity is reduced, the crumb is weakened, and the dextrins make the crumb sticky (cf. p. 67). However, flour with too high a natural alpha-amylase activity could be used for making satisfactory bread by microwave or radio-frequency baking methods (cf. p. 206). Another possibility would be to make use of an alpha-amylase inhibitor, e.g. one prepared from barley, as described in Canadian Patent No. 1206157 of 1987 (Zawistowska et al., 1988). The functions of starch in the baking of bread are to dilute the gluten to a desirable consistency, to provide sugar through diastasis, to provide a strong union with gluten, and by gelatinization to become flexib1e and to take water from the set and become rigid. Norma1 flour from sound wheat contains amp1e formation of gummy dextrins during baking and many 'prouted grains may have too high an alpha- allow the loaf to rise, must yet be strong enough gluten, a process which he1ps the gluten fi1m to bonds, including disulphide (-SS-) bonds, and Gas production and gas retention The creation of bubble structure in the dough is a fundamental requirement in breadmaking. The carbon dioxide generated by yeast activity does not create bubbles: it can only inflate gas cells already formed by the incorporation of air during mixing. Adequate gas must be produced during fermentation, otherwise the loaf will not be inflated sufficiently. Gas production depends on the quantity of soluble sugars in the flour, and on its diastatic power. Inadequate gassing (maltose value less than 1.5) may be due to an insufficiency of damaged starch or to a lack of alpha-amylase; the latter can be corrected by adding sprouted wheat to the grist, or malt flour, or fungal amylase, e.g
BREAD-BAKING TECHNOLOGY of which those that affect proteins, the proteolyt A dough undergoing fermentation, with inter- enzymes, may be of importance in baking.Yeast mittent mechanical manipulation, is said to be contains such enzymes, but they remain within ripening. The dough when mixed is sticky, but he yeast cells and hence do not influence the as ripening proceeds, it becomes less sticky and gluten The proteolytic enzymes of four are proteases more rubbery when moulded, and is more easily They have both disaggregating and protein handled on the plant. The bread baked from it solubilizing effects, although the two phenomena becomes progressively better, until an optimum may be due to distinct enzymes condition of ripeness has been reached If ripening The undesirable effect on bread quality of flour is allowed to proceed beyond this point a deteriora tion sets in, the moulded dough gets shorter and milled from wheat attacked by bug(cf. p. 9) possibly sticky again, and bread quality becomes is generally considered to be due to excessive poorer.A ripe dough has maximum elasticity proteolytic activity. Inactivation temperature is after moulding and gives maximum spring in the lower for proteolytic enzymes than for diastatic oven; a green or underripe dough can be stretched enzymes, and heat treatment has been recom but has insufficient elasticity mended as a remedy for excessive proteolytic overripe dough tends to break when stretched activity in buggy wheat flour. However, it is difficult to inactivate enzymes by heat treat If the optimum condition of ripeness persists ment without damaging the gluten proteins over a reasonable period of time the flour is to have good fermentation tolerance. Weak flours simultaneously quickly reach a relatively poor optimum, and have poor tolerance, whereas strong flours give Surfactants a higher optimum, take longer to reach it, and These substances act as dough strengtheners, to have good tolerance. Addition of improvers or help withstand mechanical abuse during proces- oxidizing agents to the flour can speed up the rate sing, and they also reduce the degree of retro- at which dough ripens and hence shorten the time gradation of starch(cf. pp. 62 and 209). They taken to achieve optimum developme include calcium and sodium stearoyl lactylate (CSL, SSL and mono- and di-acetyl tartaric Dough stickiness esters of mono- and di-glycerides of fatty acids (DATEM), and are used at levels of about 0.5% disease resistance in wheat have been achieved on flour wt (Hoseney, 1986). The Bread and by incorporating genes from rye. The short arn Flour Regulations 1984 permit the use of SSL of the rye chromosome IR has been substituted up to a maximum of 5 g/kg of bread, in all bread for the short arm of the homologous group 1 and of DatEM esters, with no limit specified chromosome of wheat. However, the doughs in all bread made from the four of many of the substitution lines have a major defect in that they are intensely Stearoyl-2-/actylates sticky. This stickiness is not due to overmixing, Calcium stearoyl-2-lactylate(CSL)and sodium excess water or excess amylolytic activity: the factor responsible for the stickiness, introduced stearoyl-2-lactylate(SSL) are the salts of the with the rye chromosome, has not yet been reaction product between lactic and stearic acids identified(Martin and Stewart, 1991) CSL (Verv')and ssl (Emplex') are dough improving and anti-staling agents; they increase Proteolytic enzymes gas retention, shorten proving time and increase loaf volume. They increase the tolerance of dough Besides the enzymes that act on carbohydrates, to mixing, and widen the range over which good there are many other enzymes in flour and yeast, quality bread can be produced The use of CSL
BREAD-BAKING TECHNOLOGY 199 of which those that affect proteins, the proteolytic enzymes, may be of importance in baking. Yeast contains such enzymes, but they remain within the yeast cells and hence do not influence the gluten. The proteolytic enzymes of flour are proteases. They have both disaggregating and protein solubilizing effects, although the two phenomena may be due to distinct enzymes. The undesirable effect on bread quality of flour milled from wheat attacked by bug (cf. p. 9) is generally considered to be due to excessive proteolytic activity. Inactivation temperature is lower for proteolytic enzymes than for diastatic enzymes, and heat treatment has been recommended as a remedy for excessive proteolytic activity in buggy wheat flour. However, it is difficult to inactivate enzymes by heat treatment without damaging the gluten proteins simultaneously. Surfactants Dough ripening A dough undergoing fermentation, with intermittent mechanical manipulation, is said to be ripening. The dough when mixed is sticky, but as ripening proceeds, it becomes less sticky and more rubbery when moulded, and is more easily hand1ed On the plant’ The bread baked from it becomes progressively better, until an optimum condition of ripeness has been reached. If ripening is allowed to proceed beyond this point a deterioration sets in, the moulded dough gets shorter and possibly sticky again, and bread quality becomes poorer. A ripe dough has maximum elasticity after moulding and gives maximum spring in the oven; a green or underripe dough can be stretched but has insufficient elasticity and spring; an overripe dough tends to break when stretched. If the optimum condition of ripeness persists over a reasonable period of time the flour is said to have good fermentation tolerance. Weak flours quickly reach a relatively poor optimum, and have poor tolerance, whereas strong flours give a higher optimum, take longer to reach it, and oxidizing agents to the flour can speed up the rate at which dough ripens and hence shorten the time taken to achieve optimum development. Do ugh stickiness Certain agronomic advantages and improved disease resistance in wheat have been achieved by incorporating genes from rye. The short arm of the rye chromosome 1R has been substituted for the short arm of the homologous group 1 chromosome of wheat. However, the doughs made from the flour of many of the substitution lines have a major defect in that they are intensely sticky. This stickiness is not due to overmixing, excess water or excess amylolytic activity: the factor responsible for the stickiness, introduced with the rye c~romosome, has not yet been identified (Martin and Stewart, 1991). Proteolytic enzymes Besides the enzymes that act on carbohydrates, there are many other enzymes in flour and yeast, These substances act as dough strengtheners, to sing, and they also reduce the degree of retrogradation of starch (cf. pp. 62 and 209). They include calcium and sodium stearoyl lactylates (CSL, SSL) and mono- and di-acetyl tartaric esters of mono- and di-glycerides of fatty acids (DATEM), and are used at levels of about 0.5% On flour Wt (HoseneY, 1986). The Bread and Flour Regulations 1984 Permit the use of SSL, UP to a maximum of 5 g/kg of bread, in all bread, and of DATEM esters, with no limit specified, in a11 breadStearoy/-Z-/acty/ates Calcium stearoyl-2-lactylate (CSL) and sodium stearoY1-2-1actY1ate (SSL) are the salts of the reaction product between lactic and stearic acids. CSL (‘Verv’) and SSL (‘Emplex’) are dough improving and anti-staling agents; they increase gas retention, shorten proving time and increase loaf volume. They increase the tolerance of dough to mixing, and widen the range over which goodquality bread can be produced. The use of CSL have good to1erance* Addition Of improvers Or help withstand mechanical abuse during proces-
TECHNOLOGY OF CEREALS r Ssl permits the use of a considerable propor Commercial processes for making white tion of non-wheat flours in ' composite flours'to make bread of good quality by ordinary procedures (cf. p. 214). A typical composite breadmaking a white pan loaf of good quality is character maize or cassava starch 25, soya flour 5, CSL appearance as regards shape and colour, ano.a four would contain (in parts) wheat four 70 ized by having sufficient volume, an attractiy 0.5-1.0, plus yeast, sugar, salt and water. The crumb that is finely and evenly vesiculated and nutritive value of such bread has been shown soft enough for easy mastication, yet firm enough to be superior to that of bread containing only to permit thin slicing. A more open crumb wheat flour, salt, yeast and water. Use of CsL structure is characteristic of other varieties, e.g and Ssl has been permitted in the U.S.A. since Vienna bread and French bread. The attainment 1961 of good quality inherent characteristics of the ingredients particularly the flour- and partly on the baking Colour of bread crust and crumb process In the U. K. white bread comprised about The brown colour of the crust of bread 52% of the total bread eaten in the home in is probably due to melanoidins formed by a 1989. Methods used for commercial production non-enzymic ' browning reaction(Maillard type) of white bread differ principally according to the between amino acids, dextrins and reducing way in which the dough is developed This may carbohydrates. Addition of amino acids to fours be iving pale crust colour results in improvement of colour. The glaze on the crust of bread is due biologically, by yeast fermentation. Examples: in part, to starch gelatinization which occurs bulk (long) fermentation processes(Straight when the oven humidity is high. An under-ri dough system; Sponge and dough system); dough which still contains a fairly high sugar mechanically, by intense mixing and use of content will give a loaf of high crust colour oxidizing agents. Examples: J. C. Baker's conversely, an over-ripe dough gives a loaf of pale Do-Maker'process and amFLoW processes crust colour (continuous); Chorleywood Bread Process The perceived colour of bread crumb is influ Spiral Mixing Method enced by the colour, degree of bleach, and hemically, by use of reducing and oxidizing extraction rate of the flour: the use of fat agents. Example: Activated Dough Develop powder, soya flour or malt flot ment(ADD)process recipe; the degree of fermentation; the extent to which the mixing process disperses bubbles within the dough and the method of panning In the bulk fermentation process, some of the cross-panning and twisting to increase light- to alcohol and carbon dioxide. both of which are volatile and are lost from the dough(cf. p. 197 The bulk fermentation process is thus a wasteful Bread aroma and flavour method, and processes which utilize mechanical or chemical development of the dough offer The aroma of bread results from the interaction considerable economic advantages, as there is less of reducing sugars and amino compounds, accom- breakdown of the starch, as well as being much panied by the formation of aldehydes. Aroma is more rapid also affected by the products of alcoholic and, in Other rapid methods include the Continental some cases, lactic acid fermentation organic No-time process(or Spiral Mixing Method), the acids, alcohols, esters. The favour of bread Emergency No-time process and the Aeration or resides chiefly in the crust Gas-injection process
200 TECHNOLOGY OF CEREALS or SSL permits the use of a considerable proportion of non-wheat flours in ‘composite flours’ to Commercial processes for making white bread make bread Of good quality bY Ordinary procedures (cf* P* 214). A typica1 cornPosite breadmaking A white pan loaf of good quality is characterized by having sufficient volume, an attractive ‘Our wou1d contain (in parts) wheat flour 70’ maize Or caSSava starch 25’ soya flour 5’ csL 0.5-1.0, plus yeast, sugar, salt and water. The nutritive value of such bread has been shown to be superior to that Of bread containing Only wheat flour’ sa1t’ yeast and water’ Use Of csL and SSL has been permitted in the U.S.A. since 1961. appearance as regards shape and colour, and a crumb that is finely and evenly vesiculated and soft enough for easy mastication, yet firm enough to pemit thin slicing. A mOre open crumb structure is characteristic of other varieties, e.g. Vienna bread and French bread. The attainment of good quality in bread depends panly on the inherent characteristics of the ingredients - particularly the flour - and partly on the baking process. In the U.K., white bread comprised about The brown colour of the crust of bread 52% of the total bread eaten in the home in 1989. Methods used for commercial production of white bread differ principally according to the way in which the dough is developed. This may be: - biologically, by yeast fermentation. Examples: bulk (long) fermentation processes (Straight dough system; Sponge and dough system); - mechanically, by intense mixing and use of oxidizing agents. Examples: J. C. Baker’s ‘Do-Maker’ process and AMFLOW processes (continuous); Chorleywood Bread Process; Spiral Mixing Method; - chemically, by use of reducing and oxidizing agents. Example: Activated Dough Development (ADD) process. Colour of bread crust and crumb is probably due to melanoidins formed by a non-enzymic ‘browning reaction’ (Maillard type) between amino acids, dextrins and reducing carbohydrates. Addition of amino acids to flours giving pale crust colour results in improvement of colour. The glaze on the crust of bread is due, in part, to starch gelatinization which occurs when the oven humidity is high. An under-ripe dough which still contains a fairly high sugar content will give a loaf of high crust colour: conversely, an over-ripe dough gives a loaf of pale crust colour. The perceived colour of bread crumb is influenced by the colour, degree of bleach, and extraction rate of the flour; the use of fat, milk powder, soya flour or malt flour in the recipe; the degree of fermentation; the extent within the dough and the method Of panning - cross-panning and twisting to increase lightreflectance. to which the mixing process disperses bubb1es In the bulk fermentation process, some of the starch, after breakdown to sugars, is converted to alcohol and carbon dioxide, both of which are volatile and are lost from the dough (cf. p. 197). The bulk fermentation process is thus a wasteful method, and processes which utilize mechanical or chemical development of the dough offer Bread aroma and flavour The aroma of bread results from the interaction considerable economic advantages, as there is less of reducing sugars and amino compounds, accom- breakdown of the starch, as well as being much panied by the formation of aldehydes. Aroma is more rapid. also affected by the products of alcoholic and, in Other rapid methods include the Continental some cases, lactic acid fermentation - organic No-time process (or Spiral Mixing Method), the acids, alcohols, esters. The flavour of bread Emergency No-time process and the Aeration or resides chiefly in the crust. Gas-injection process