谷物食品技术（英文版）：08338_08

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 three- dimensional 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 expan- sion 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 191 192 TECHNOLOGY OF CEREALS are three stages in the manufacture of bread: mixing and dough development, dough aeration, and oven baking. The method of dough develop- ment 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 specifica- tions 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+ E- PJ\@-\@&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 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 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 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 associa- proportion 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. More- over, 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 produc- tion 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 import- ant. 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 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 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-&lactone. One hundred grams two enzymes maltose permease and maltase (alpha- of 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 formula- a 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 temper- ature is increased within a fixed time process. Until the early 1970s, two strains of Saccharo- In 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 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 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 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 com- pressed 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, 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 appear- ance, 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. 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 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, 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. 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, prob- Units of fungal amylase is so powerful that it may ably assisted by the lipoxidase enzymes (cf. 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 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 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 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 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 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 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. 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 collec- tively 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 inter- and intra-proteidpolypeptide relationships to be formed via -SS- bonding, one effect of this inter- change being the relaxation of dough by the relief of stress induced by the mixing process. While gluten is important in creating an extens- ible 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 bak- ing, 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 fermen- tation, otherwise the loaf will not be inflated suf- ficiently. 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 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 recom- mended as a remedy for excessive proteolytic activity in buggy wheat flour. However, it is difficult to inactivate enzymes by heat treat- ment without damaging the gluten proteins simultaneously. Surfactants Dough ripening A dough undergoing fermentation, with inter- mittent 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 deteriora- tion 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 retro- gradation 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 bread- Stearoy/-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 good- quality bread can be produced. The use of CSL have good to1erance* Addition Of improvers Or help withstand mechanical abuse during proces- 200 TECHNOLOGY OF CEREALS or SSL permits the use of a considerable propor- tion 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 character- ized 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 Develop- ment (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 influ- enced 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 light- reflectance. 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. BREAD-BAKING TECHNOLOGY 201 added to flour at the recommended levels, will add not more than 150 mg/kg of ascorbic acid and/or 35 mg/kg of azodicarbonamide. After about 2 h in a 3 h fermentation process, the dough is 'knocked back', i.e. manipulated to push out the gas that has been evolved in order to even out the temperature and give more thorough mixing. After another hour's rising, the dough is divided into loaf-sized portions and these are roughly Straight dough system In a representative procedure, the ingredients shaped. The dough pieces rest at about 27°C for for a 100-kg 3-h dough would be 100 kg of flour, 10-15 min. ('1st proof') and are then moulded with probably 1 kg of yeast, 2 kg of salt, 1 kg of into the final shape, during which the dough is fat and 55-57 kg of water at a temperature that mechanically worked to tighten it so that the gas will bring the mixture to about 27°C after mixing. is better distributed and retained, and placed in Until the prohibition of its use in the U.K. in tins. The final mould is very important in giving April, 1990 (MAFF, 1990), potassium bromate good texture in bulk-fermented bread. It is dur- would generally have been added to the flour by ing the rounding and moulding processes that the miller at a rate of 15 mg/kg. The yeast is the bubble structure, resulting in a satisfactory dispersed in some of the water, the salt dissolved crumb structure, is developed: bubbles that have in another portion. All these ingredients, together been inflated during the fermentation are sub- with the rest of the water, are then blended and divided to produce a greater number of smaller mixed in a low speed mixer during 10-20 min, bubbles. during which there may be a temperature rise of The dough rests again in the tins for the final 2°C. The resulting dough is set aside while proof of 45-60 min at 43°C and 8045% r.h., fermentation proceeds. and it is the carbon dioxide evolved during the As an alternative to treatment of the flour with final proof that inflates the dough irreversibly. potassium bromate, the miller can use ascorbic The dough is then baked in the oven at a acid at a rate of 15 mg/kg, or azodicarbonamide temperature of 235°C for 20-40 min, depending at a level of 5 mg/kg. If the bulk fermentation on loaf size, with steam injected into the oven to time is 1 h or longer, no further treatment of produce a glaze on the crust. the flour with oxidizing agents by the baker is A number of changes take place as the temper- required. For use in a bulk fermentation process ature of the dough rises at the beginning of of 30 min or less, the baker would probably add baking: a further 50-100 mg/kg of ascorbic acid or 20- 30 mg/kg of azodicarbonamide, as one of the - the rate of gas production increases; functions of oxidizing agents is to shorten the - at about 45°C the undamaged starch granules fermentation time. begin to gelatinize and are attacked by The Bread and Flour Regulations 1984 permit the use, in the U.K., of up to 200 mg/kg of ascorbic acid in all bread, and of up to 45 mg/kg of azodicarbonamide in all bread except whole- meal. To avoid the accidental breaching of these Regulations, a Code of Practice has been agreed, by which millers will add not more than 50 mg/kg of ascorbic acid and/or 10 mg/kg of azodicarbon- amide to flour at the mill, while improver manu- facturers will ensure that their products, when Bulk (long) fermentation process The bread is made by mixing a dough from flour, water, yeast, fat and salt, allowing the dough to rest at a temperature of 26"-27°C while fermentation and gluten ripening take place, and then baking in the oven. alpha-amylase, yielding fermentable sugars; - between 50" and 60°C the yeast is killed; - at about 65°C the beta-amylase is thermally - at about 75°C the fungal amylase is inactivated; - at about 87°C the cereal alpha-amylase is inactivated; - finally, the gluten is denatured and coagu- lates, stabilizing the shape and size of the loaf. inactivated; 202 TECHNOLOGY OF CEREALS Sponge and dough system When the bulk fermentation process is used in England, the straight dough system is generally employed. But in the U.S.A., to some extent in Scotland, and occasionally in England, a sponge and dough system is used. straight dough system in that only part of the flour is mixed at first with some or all of the yeast, some or all of the salt, and sufficient water to make a dough, which is allowed to ferment for some hours at 21°C. The sponge (as this first dough is called) is then broken down by remixing, and the remainder of the flour, water and salt, and all the fat added to make a dough of the required consistency. Addition of oxidizing agents - ascorbic acid alone or ascorbic acid plus azodicarbonamide - would usually be made at the dough stage’ The dough is given a short fermentation at 27°C before proving and baking. Further details of the procedure are to be found bakeries, peel, reel or rack ovens have now largely replaced drawplate ovens. In larger bakeries, so- called ‘travelling’ ovens are used. In these, the doughs are placed on endless bands which travel through the oven. The oven is tunnel-shaped and possibly 18.3 m (60 ft) long. The Bulk Fermentation Process is now used mercially-made bread in the U.K. : the principal users would be plant bakeries in Scotland and small bakeries, some of which prefer the sponge and dough system. Mechanical development processes Continuous doughmaking A further stage in the mechanization of bread- making is represented by the continuous bread- making process, exemplified by the Wallace and Tiernan Do-Maker Process, based on the work of J. C. Baker, which was formerly used in the The sponge and dough system differs from the to make probably not more than 10% of all corn- in The Master Bakers’ Book Of Breadmaking (Brown, 1982)* The sponge and dough system is U.K. and the U.S.A. About 35% of U.S. bread was made by the Baker process in 1969. In the said to produce bread that has a fuller flavour than that made by the straight dough system. A Bakers’ Grade flour of, say, 12% protein content stage requires a stronger flour of, say, 13% protein content. About 65% of all bread in the U.S.A. is made by the sponge and dough system. process, first used in the U.K. in 1956 (see Anon., 1957), the flour, spouted from a hopper, is continuously mixed with a liquid pre-ferment or pre-ferment is a mixture consisting of a sugar solution with yeast, salt, melted fat and oxidizing agents which is fermented for 2-4 h. The dough is allowed no fermentation time, but instead is subjected to intense mechanical mixing whereby the correct degree of ripeness for proving and baking is obtained. In the absence of fermenta- tion, it is essential to incorporate an appropriate quantity of oxidizing agent into the dough. The dough is extruded through a pipe, cut off into loaf-sized portions, proved and baked. The Do- Maker Process gives bread with a characteristic and very even crumb texture. Considerable time is saved, in comparison with bulk fermentation processes. The AMFLOW process has an overall similarity to the Do-Maker process, but features a multistage pre-ferment containing flour, and a horizontal, In the U.S.A., the Do-Maker and AMFLOW is suitab1e for the dough stage, but the sponge ‘brew) in electronically regulated quantities. The Plant baking In the small bakeries, most of the processes of dividing, moulding, placing in the proving cabinets and the oven and withdrawing therefrom are carried out by hand. However, disadvantages of hand-processing are lack of uniformity in the products and the excessive amount of labour involved. In large bakeries, machines carry out all these processes. Mixers are of the closed bowl high-speed type, consuming a total quantity of energy (including no-load power) of 7.2-14.4 kJ1 kg (1-4 Wh/kg) and taking 15-20 min. Dough dividers divide the dough by volume: automatic provers have built-in controls giving correct instead of a vertical, development chamber. temperature and relative humidity. In the smaller BREAD-BAKING TECHNOLOGY 203 processes are being replaced by the sponge and the bread grist, it will be desirable for the miller dough processes or by the CBP. The Do-Maker to formulate the grist in such a way that the work and AMFLOW processes are no longer used in input requirement is maintained at, or near, the U.K. 11 Wh/kg. For an average grist, the quality of the bread, in respect of loaf volume and fineness of crumb structure, improves at work input levels from 7 to 11 Wh/kg, but at 13 Wh/kg or more Chorle ywood Bread Process (CBP) This is a batch or continuous process in which the structure of crumb deteriorates. Work input dough development is achieved during mixing by level is monitored by a watt-hour meter and a intense mechanical working of the dough in a counter unit attached to the mixer motor. The short time, and bulk fermentation is eliminated. total work input required - dough wt in kg x The process was devized in 1961 by cereal scientists 11 - is set on the counter unit, and the mixer and bakers at the British Baking Industries motor is automatically switched off when the Research Association, Chorleywood, Herts, determined amount of work has been performed. England (Chamberlain et al., 1962; Axford et al., One reason for the intense and rapid mixing is 1963). It is necessary to use a special high-speed that it brings the molecules rapidly into contact mixer for mixing the dough. The process is with the oxidizing agents. During the intense characterized by: mechanical development, a gas bubble structure is created in the dough which, provided the dough - the expenditure of a considerable, but care- is properly handled, is expanded in proof and fully controlled, amount of work (1 1 Wh/kg; becomes the loaf crumb structure. 40 J/g) On the dough during a period Of 24 Final dough temperature after mixing should min; be 28"-30"C, but as the mixing process causes a - chemical oxidation with ascorbic acid (vitamin temperature rise of 14"-15"C, the doughing water C) alone or with potassium bromate (if allowed) may have to be cooled, and a water-cooling unit at a relatively high total level, viz. 100 mg/ is generally a part of the plant. kg, or with azodicarbonamide at a level of 20- The use of potassium bromate is no longer azodicarbonamide; not used as an oxidizing agent, the use of ascorbic - addition of fat (about 0.7% on flour wt) - acid instead, at a level of 100 mg/kg, may not be this is essential - of which 5% (0.035% on adequate to maintain loaf volume if the dough flour wt) should be high melting point fat is mixed under partial vacuum. Under these conditions, the use of azodicarbonamide at a level which will still be solid at 38°C; - use of extra water (3.5% more than normal, of 20-30 mg/kg, in addition to the ascorbic acid, would be beneficial (cf. p. 176). based on flour wt); - absence of any pre-ferment or liquid ferment; To achieve the full oxidation potential of the - a higher level of yeast, 2% on flour wt, than ascorbic acid, an adequate concentration of oxygen in the mixing machine bowl is essential: this is used in the BFP; - a first proof of 2-10 min, after dividing and requirement may be partially met by eliminating rounding, followed by conventional moulding the vacuum, so that the dough is mixed in air, and final proof. or, more effectively, by filling the head space of The level of work input is critical, but is the mixer with an oxygen-enriched atmosphere, dependent on the genetic make-up or strength of e.g. 60% oxygen/40% nitrogen, equivalent to a the wheat. Thus, while a figure of 11 Wh/kg is 50/50 mixture of oxygen and air. applicable to dough made from an average grist, Further improvement in loaf volume, if potas- there are certain U.K. wheat varieties, e.g. Fresco, sium bromate is not being used, could be achieved the flour from which, if used alone, would require by changing to a flour of slightly higher protein 17-20 Wh/kg. If such varieties are included in content or by adding vital gluten, by increasing 30 mg/kg Or with both ascorbic acid and perfitted in the U.K.; if potassium bromate is 25-40 min BREAD-BAKING TECHNOLOGY 205 L-cysteine hydrochloride (corresponding to about 27 mg/kg of L-cysteine) with 25 mg/kg of potas- sium bromate plus 50 mg/kg of ascorbic acid. These levels are based on the use of flour of 12% protein content that has already been treated at the mill with up to 20 mg/kg of potassium bromate. The ADD process was introduced to the baking industry by the British Baking Industries Research Association in 1966, but the process could not be used commercially in the U.K. until 1972, when the use of L-cysteine hydrochloride was permitted by the Bread and Flour (Amendment) Regulations 1972 (MAFF, 1972). Potassium bromate and ascorbic acid were listed in the Bread and Flour Regulations 1984 (MAFF, 1984) as permitted improvers, but potassium bromate was removed from the list of improvers permitted in the U.K. the reformulation of additives used in the ADD. Replacement of potassium bromate by additional ascorbic acid or azodicarbonamide (within the maximum permitted limits) is not an ideal solu- tion, as the balance between the oxidizing and reducing agents is upset, and hence, ADD is no longer a viable method in the U.K. Chemical development process The optimum work input for mechanical dough development is lowered if a proportion of the disulphide bonds are broken chemically by the introduction of a reducing agent. The Activated Dough Development process (ADD) achieves dough development without either bulk fermentation or mechanical develop- ment. A relatively rapid-acting reducing agent, L-cysteine, and a relatively slow-acting oxidizing agent, potassium bromate, or a mixture of potas- sium bromate and ascorbic acid, are added at the dough mixing stage, using conventional, low- speed, mixing equipment. All the ingredients, which include 2% of yeast, 0.7-1.0% of fat, and extra water, as for the CBP, are mixed together for 10-20 min, and the dough temperature after accelerates the uncoiling and reorientation of the protein molecules and the oxidizing agent follows up by stimulating the formation of cross links to stabilize the desired elastic three-dimensional gluten network. During mixing, air is entrained in the dough, starting the process of cell formation which is continued throughout the subsequent stages of dough dividing, rounding, first proof of 6-10 min, and final moulding. During the final proof of 45-55 min (as for the BFP and the CBP) sufficient gas to inflate the dough is produced by activity of the yeast. The ADD requires the use of a Bakers’ Grade flour of about 12% protein content as used in the BFP; the lower protein content flours used in the CBP are not suitable for the ADD. Apart from this restriction on flour quality, the ADD offers most of the advantages over the BFP that are claimed by the CBP and, in addition, the ADD does not require the use of a special high-speed mixer. The ADD was used by hot-bread shops, in- store bakeries and family bakers, and accounted for 5-10% of all bread made commercially in the U.K. The usual levels of addition of reducing and oxidizing agents are 35 mg/kg on flour wt of mixing shou1d be 280-300c’ The reducing agent in April, 1990 (MAFF, 1990), thereby necessitahg EC policy regarding additives Additives will only be included in a permitted list if a reasonable technological need is demon- strated, and if this need cannot be achieved by other means that are economically and techno- logically practicable. Furthermore, the additives must present no hazard to health at the levels of use proposed, and they must not mislead the customer. ‘Need’ is understood to mean preservation of nutritional quality; the meeting of special dietary requirements; enhancement of keeping quality, stability and organoleptic properties; or providing aid in manufacture, processing, preparation, treatment, packaging, transport or storage. Specified additives are to be allowed only in specified foods, and at levels not exceeding those required to achieve the desired effect (Spencer, 1989). 206 TECHNOLOGY OF CEREALS Other rapid methods No-time continental process This process, also known as the Spiral Mixing Method, avoids a long bulk-fermentation, the use of a high-speed mixer, and the addition of L- cysteine and potassium bromate. In this process, all the ingredients are mixed together for 8-11 min in a special open-bowl mixer equipped with a spiral-shaped beater; the action of the mixer is faster and more vigorous than that of the low- speed mixers used in the BFP, but not so intense as that which is necessary for the CBP. The mixing action incorporates more air, and hence oxygen, in the dough, thereby improving cell creation and increasing the effectiveness of ascorbic acid. The ingredients used would include a higher processes, 2% of salt, about 60 pt of water per 100 pt of flour, fat, ascorbic acid, emulsifier, fungal amylase and sugar. The dough temperature fermentation (15-30 min) follows mixing. This process is widely used on the Continent of Europe and is being used increasingly in the U.K., particularly in small bakeries. mixing soda water (water charged with carbon dioxide gas) and flour under pressure. When the pressure was released the dough expanded and was immediately divided and baked. The whole process, including baking, took 90 min. A modern equivalent is the Oakes Special Bread Process, a continuous system in which carbon dioxide gas is injected into the developing dough. Neither process is in commercial use for making standard bread. Microwave and radio frequency baking The use of microwave (MW) energy for baking bread was investigated at the Flour Milling and Baking Research Association (FMBRA), Chorleywood, England, (Chamberlain, 1973). Microwave energy, generated by a magnetron, and transmitted by radiation of frequency from very rapidly and cooks the loaf uniformly throughout. Another source of energy that has been investi- 27 MHz, which similarly heats the loaf rapidly throughout. Commercial application of MW baking has not so far (1992) been possible because of the unavail- ability of a thermostable material for the pans which has the mechanical properties of metal but is freely permeable to microwave radiation. It is reported that the RF method can be operated with Conveyors, baking pans and foil containers made of metal, and RF Ovens are now commer- cially available for making bread, biscuits and other cereal-based products. In both MW and RF baking, the dough is held for only a short period within the temperature range at which the activity ofalpha-amylase is un- welcome, thereby permitting the use of a wheat grist of figher alpha-mylase activity than would be acceptable for conventional baking. Moreover, in conventional baking, the gases evolved are rapidly lost unless the protein content of the flour is high enough - say 10.5'/0 or more - to confer adequate strength to the walls of the crumb cells. In both MW and RF baking, however, the rate of gas production exceeds the rate of gas loss level Of yeast (3% On flour wt> than used in Other about 900 MHz upwards, penetrates the dough aimed at is 26"-28"c. A short period Of bu1k gated is radio frequency (RF) energy, of about Emergency no-time dough This is a Short System, Somewhat resembling the No-time Continental process, that is used occasionally in the U.S.A. and the U.K., particu- larlY for emergency Production- The dough is made, using a larger amount of yeast, e.g. 2.5% on flour wt, and a higher temperature, e.g. 30"-32"C, than are Usual for normal fermentation systems, and is immediately scaled off. Final moulding follows after about 15 mi% and the dough Pieces are Proved for 1 h at 43°C before baking. The bread has a coarse, thick-walled crumb structure, and it stales rapidly. Aeration (gas-injection) process In 1860 Dauglish described a rapid bread- making method in which a dough was made by BREAD-BAKING TECHNOLOGY 207 attractive crispness of freshly baked bread is lost. Extensive drying during cooling results in weight loss (and possible contravention of the Weights and Measures Act in the U.K.), and in poor crumb characteristics. The aim in cooling is therefore to lower the temperature without much change in moisture content. This may be achieved by subjecting the loaves to a counter-current of air conditioned to about 21°C and 80% r.h. The time taken for cooling 800 g loaves by this method (because the dough is heated rapidly throughout): hence, high protein content in the flour is not obligatory. In fact, flour of 7.5% protein content was used experimentally at the FMBRA to produce bread by MW baking that compared favourably with bread conventionally baked from flour of normal protein content. Thus, a further impetus towards the commercial application of RF heating would be a substantial price differential in favour of west-European wheat (of lower protein content, and often of high alpha-amylase activity) as is 2-3 h. against imported, non-EC, strong wheat. Baking by MW or RF alone produces crustless Automation bread. A crust can be developed by applying thermal radiation, in the form of hot air, simul- Recent developments that increase the efficiency taneously during a total baking time of less of the plant baking process include the use of load than 10 min for a standard 800 g loaf. The Air cells for weighing the ingredients and controlling Radio Frequency Assisted (ARFA) oven there- ingredient proportions in the mixer, and the use fore combines air radio frequency and convected of the microelectronics for temperature corrective hot air in a technique developed by the Electricity feedback and consistency corrective feedback Council Research Centre, Capenhurst, England (Baker, 1988). Another development is the intro- (Anon., 1987, 1988b). However, there is to date duction of computer-programmed mixers and (1992) no known commercial application of ARFA plants. for breadmaking. Bread moisture content There is no legal standard for the moisture Frozen dough The use of frozen dough, which can conveniently content of bread in the U. K. The moisture be stored, has recently increased in popularity, content of American and of Dutch bread must e.g. for in-store bakeries. The best results are not exceed 38%. In Australia the maximum obtained if ascorbic acid is used as the oxidant, permitted moisture content in any portion weighing and if the doughs are frozen before fermentation 5 g or more is 45% for white bread, 48% for brown and then stored at a constant temperature to and wholemeal. In New Zealand, 45% is the avoid problems associated with the melting of ice maximum moisture content similarly permitted crystals. in any bread. Bread cooling Bread weights The cooling of bread is a problem in mechanical production, particularly when the bread is to be wrapped and/or sliced before sale. Bread leaves the oven with the centre of the crumb at a temperature of about 96°C and cools rapidly. During cooling, moisture moves from the interior outwards towards the crust and thence to the atmosphere. If the moisture content of the crust rises considerably during cooling, the texture of the crust becomes leathery and tough, and the In the U.K., standard bread weights were 1 lb and 2 lb until 6 May 1946, when weights were reduced to 14 oz and 28 oz. From 1 May 1978 loaves sold in the U.K. weighing more than 300 g (10.6 oz) were required to weigh 400 g or a multiple of 400 g. In Belgium, loaves weighing more than 300 g must weigh 400 g or multiples of 400 g. In Germany, prescribed weights for unsliced bread were 500 g and then multiples of 250 g up to 208 TECHNOLOGY OF CEREALS 2000 g, and above 2000 g by multiples of 500 g. averages 40%, thus giving a practical requirement Prescribed weights for sliced bread were 125 g, of 1 MJ (948 Btu) per nominal 800 g loaf plus pan: 250 g, and then by multiples of 250 g to 1500 g, 750 kJ (71 1 Btu) for the 800 g loaf alone, equivalent and then by multiples of 500 g to 3000 g. to 937 kJ (889 Btu) per kg of bread (without pan). From 1980, enforcement of bread weight Additional energy is used in conveyors, final regulation in the U.K. has taken place at the point proof, cooling, slicing, wrapping of bread, but of manufacture rather than, as formerly, at the these amounts are small in relation to the point of sale, and is based on the average weight energy used for baking (Cornford, S. J., private of a batch rather than on the weight of an communication, 1979). individual loaf. A breakdown of the total energy requirements for making a white loaf, including energy used in growing the wheat, milling the wheat, baking the bread, and selling the bread, is shown in Table 8.1. Yield of bread Using the CBP, 100 kg of white flour at 14% m.c. produce an average 180 loaves of nominal TABLE 8.1 weight 800 g (average 807 g) containing an Energy Requirements for Making a White Loaf average of 39% of moisture (total bread yield from 100 kg of flour: 145 kg of bread). Thus, a nominal Percentage of total energy required 800 g loaf is made from an average of 556 g of flour at natural m.c. (478 g on dry basis) and Tractors 5.3 Fertilizers 11.1 3.0 19.4 14 g of dry matter are contributed by non-flour Drying, sprays constituents). Milling the wheat Direct fuel and power 7.4 Other 2.1 Energy consumption in making bread Packaging 1.3 Transporting 2.0 12.8 30.2 800 g loaf, for the mixing process. The bulk ~~~t~~~dpower 17.3 fermentation process uses about one-fifth of this Packaging 9.0 amount for mixing, but some additional energy Transporting 7.8 64.3 99.9 Growing wheat contains on average 492 g of dry matter (i.e. The CBP uses 40 J/g of dough, or 35.7 kJ per Baking Shops 3.4 3.4 is used in heating the water for doughmaking. In the baking process, the heat required com- prises the heat needed to raise the temperature of the dough piece from that of the prover (about 40°C) to that at the oven exit (about 96°C); the latent heat of evaporation of the water changed to steam, and the heat required to raise the temperature of that steam to that of the oven; and the heat required to raise the temperature of the pan to the oven exit temperature. Thus, for baking a nominal 800 g loaf (with flour at 14% m.c., water absorption 60.7% on flour wt, and oven loss 65 g), about 400 kJ (379 Btu) theoretical are required. This figure is made up of about 300 kJ (284 Btu) for the loaf itself plus about 100 kJ (95 Btu) for the pan. Oven efficiency depends on oven type and quantity of steam used for conditioning the oven atmosphere, and Data from Leach (1975). Other kinds of bread Brown and wholemeal breads When using the bulk fermentation process, the level of fat used in brown and wholemeal breads is generally raised to about 1.5% on flour wt (as compared with 1% for white bread) because the fat requirement for brown flour and wholemeal is more variable than that for white flour. With the CBP, it is essential to raise the fat level in this way for brown and wholemeal breads. A short fermentation system is generally used for wholemeal bread. For example, the dough BREAD-BAKING TECHNOLOGY 209 to sprout, kiln dried and rolled. To this is added might be allowed to ferment for 1 h before knocking back, plus 30 min to scaling and barley malt. moulding, at an appropriate yeast level and temperature. Wheat germ bread This is made from white flour with the addition of not less than 10% of processed germ (cf. p. 153) which has been heat-treated to stabilize the lipid content and to destroy glutathione, a Bread staling component which has an adverse effect on bread quality. A fermentation process to inactivate glutathione, as an alternative to heat treatment, Staling of bread crumb is not a drying-out was described in Australia in 1940. process: loss of moisture is not involved in true crumb staling. The basic cause of staling is a slow change in the starch, called retrogradation, at temperatures below 55°C from an amorphous to Gluten bread: High-protein bread These breads are made by supplementing flour a crystalline form, the latter binding considerably with a protein source, such as wheat vital gluten, less water than the former. This change leads to whey extract, casein, yeast, soya flour. Procea a rapid hardening, a toughening of the crust and and Slimcea are proprietary breads in which the firming of the crumb, loss of flavour, increase in additional protein is provided by wheat gluten. opaqueness of the crumb, migration of water However, most bread now made in the U.K. from crumb to crust, and to shrinkage of the and in numerous other countries contains a starch granules away from the gluten skeleton small amount of added vital wheat gluten (cf. p. with which they are associated, with consequent 195) depending on the protein content of the development of crumbliness (Hoseney, 1986). flour. The rate at which staling proceeds is dependent on the temperature of storage: the rate is at a maximum at 4"C, close to the temperature inside a domestic refrigerator, decreasing at temper- High-fibre bread This bread has both higher fibre content and atures below and above 4°C. Staling can be fewer calories per unit than normal bread. The prevented if bread is stored at temperatures above high fibre content is achieved by addition of 55°C (although this leads to loss of crispness various supplements, such as cracked or kibbled and the probability of rope development) or at wheat, wheat bran, or powdered cellulose. A type -2O"C, e.g. in a deep freezer. of cellulose used in the U.S.A. , called Solka-Floc, As the amylose (straight-chain) portion of the is delignified alpha-cellulose obtained from wood; starch is insolubilized during baking or during usage levels are 5-10%. The use in the U.K. of the first day of storage, it is considered that alpha-cellulose or the sodium salt of carboxymethyl staling is due to heat-reversible aggregation of cellulose in bread, for which a slimming claim is the amylopectin (branched-chain) portion of the made, is permitted by the Bread and Flour starch. Regulations 1984 (MAFF, 1984). However, starch crystallization cannot account for all the crumb firming that occurs at temper- atures above 21"C, and it has been suggested by Willhoft (1973) that moisture migration from Granary bread This is a proprietary bread made from a protein to starch occurs, leading to rigidification mixture of wheat and rye which has been allowed of the gluten network, and contributing to crumb Speciality breads Other 'special' breads include pain d'ipice, fruit breads, malt loaves, mixed grain bread, bran bread, etc. Bread staling and preservation 210 TECHNOLOGY OF CEREALS firming. See reviews of the subject by Radley (1968) and Elton (1969); see also Pomeranz (1971, 1980), and Pomeranz and Shellenberger (1971). Emulsifiers like monoglycerides retard the rate of starch retrogradation. Monoglycerides, when added at the mixing stage, first react with free, soluble amylose to form an amylose-lipid complex. When the rate of addition exceeds 1%, all the free amylose is complexed and the monoglycerides begin to interact with the amylopectin, thereby retarding retrogradation (Krog et al., 1989). bread is also permitted legally in Denmark, Germany, Italy, the Netherlands and Spain. Other means of preservation include the use of sorbic acid-impregnated wrappers, y-irradiation with 5 x lo5 rad, or infra-red irradiation. Gas-packaging, with an atmosphere of carbon dioxide, nitrogen or sulphur dioxide replacing air, has been used in an attempt to extend the mould-free shelf life of baked goods. However, even in an 'anaerobic environment' of 60% COZ plus 40% N2 the fungi Aspergillus niger and Penicillium spp. may appear after 16 days unless the concentration of oxygen can be kept at 0.05% or lower. The use of impermeable packaging to prevent entry of oxygen is very expensive; a less expensive alternative is to include an oxygen absorbent, such as active iron oxide, in the packaging. By this means, the mould-free shelf (Smith et al., 1987). A so-called '90-day loaf' is packaged in nyloll- polypropylene laminate and the interior air partly replaced by carbon dioxide. The packaged loaf is then sterilized by infra-red radiation. None of these methods prevents the onset of true staling. Freezing Freezing of bread at -20°C is the most favourable method of preserving the freshness of bread. Suitably packed, the bread remains usable almost indefinitely. Part-baking of soft rolls and French bread is a technique now widely used in hot bread shops, Bread preservation The expected shelf-life of bread made in the in-store bakeries, bake-off units in non-bakery U.K. is about 5 days for white, 3-4 days for shops, catering establishments, and domestically. wholemeal and brown, and 2-3 days for crusty. In this process, doughs for soft rolls would be Thereafter, bread becomes unacceptable because proved at about 43°C and 80% r.h., those for of staling, drying out, loss of crispness of crust, French bread at about 32°C and 70% r.h. The or mould development. proved doughs are then baked just sufficiently to Mould development can be delayed or prevented kill the yeast, inactivate the enzymes and set the by addition of propionic acid or its sodium, structure, but producing little crust colour or calcium or potassium salts, all of which are moisture loss. Temperature for part-baking would permitted by the Bread and Flour Regulations be about 180°C. The part-baked product can then 1984 at levels not exceeding 3 g/kg flour (calculated be deep-frozen at, say, - lS"C, or stored at as propionic acid), or by addition of sorbic acid ambient temperature until required. The final (not permitted in the U.K. or the U.S.A.). Use bake-off at the point of use, at a temperature of propionic acid to delay mould development in of about 280"C, defrosts the frozen product, Rope Freshly-milled flour contains bacteria and mould spores, but these normally cause no trouble in bread under ordinary conditions of baking and of bacteria are killed at oven temperature, but spores of some of the bacteria survive, and may proliferate in the loaf if conditions are favourable, causing a disease of the bread known as 'rope'. Ropy bread is characterized by the presence in the crumb of yellow-brown spots and an objection- able odour. The organisms responsible are members of the B. subtilis var. mesentericus group and B. lichenzformis. Proliferation of the bacteria is discouraged by acidic conditions in the dough, e*g. by addition Of 5*4-7'1 g Of ACP Or 9 m1 Of 12% acetic acid per kg of flour. storage* Mou1d 'pores and the vegetative forms life of crusty rolls has been increased to 60 days BREAD-BAKING TECHNOLOGY 21 1 increases the crust colour to normal, and reverses breadmaking purposes. Rye flour with high all the staling that may have taken place. maltose figure (e.g. 3.5) and low amylograph value (350 or less) is of poor baking quality. Rye flours with Falling number (cf. p. 183) below 80 use Of cerea’s Other than wheat in bread produce loaves with sticky crumb, but rye flour The statement of Atkins (1971) that “bread is with FN 90-110 can be processed into acceptable fundamentally foamed gluten” can be correctly bread with the aid of additives, acidifiers and applied only to bread in which wheat flour or emulsifiers to compensate for the effects of sprout meal is the sole or dominant cereal, because the damage. Such additives would include an acidifier protein in other cereals, on hydration, does not to adjust the pH to 4.0-4.2, 2% of salt (on flour form gluten which is comparable in rheological wt), 0.2-0.5% of emulsifier, 1-3% of gelatinized properties with wheat gluten. flour (Gebhardt and Lehrack, 1988). The flour of cereals other than wheat is used Deterioration of baking quality of rye during for breadmaking in two ways: either blended with storage is better indicated by glutamic acid wheat flour, in a form sometimes known as decarboxylase activity than by Falling Number ‘composite flour’ (cf. p. 214), or as the sole cereal (Kookman and Linko, 1966). component. Bread made from composite flour The possibility that rye may be infected, in the employs conventional baking processes, but when field, with ergot (Claviceps purpurea) has been a non-wheat flour is used alone it is usual to make discussed elsewhere (cf. p. 15). use of a gluten substitute (cf. p. 215). Rye flour, The protein in rye flour is less important than however, is exceptional in that bread made from the protein in wheat flour. The rye protein, when it as the sole cereal component does not require hydrated, does not form gluten because the the addition of a gluten substitute. proportion of the protein that is soluble is much larger in rye than in wheat (up to 80% soluble in rye sour dough as compared with 10% soluble Rye protein in wheat dough), and because the high Rye flour and meal are used for the production content of pentosans inhibits the formation of of numerous types of bread, both soft bread gluten (Drews and Seibel, 1976). Conversely, the and crispbread, and rye is regarded as a bread pentosans and starch in rye are much more grain in Germany and in most Eastern European important than in wheat (Telloke, 1980). The countries (Drews and Seibel, 1976). pentosans, which comprise 47% of rye flour, and In Europe, ‘rye bread’ is made from all rye the starch have an important water-binding func- flour; ‘rye/wheat bread’ contains not less than tion in forming the crumb structure of rye bread. 50% of rye flour, with wheat flour making up the The pentosans, in particular, play a role in raising remainder; ‘wheadrye bread’ implies a blend of the viscosity of rye dough. Rye flour can be fraction- not less than 50% of wheat flour plus not less ated according to particle size to yield fractions than 10% of rye flour. which vary in starch and pentosan contents. These Factors that influence the baking potential fractions can then be blended to give an optimal of rye flour include variety, environmental condi- ratio of pentosan to starch. A pentosan:starch tions of growth and fertilizer use, activity of ratio of 1:16 to 1:18 is considered ideal. amylase, protease and pentosanase enzymes, and The starch of rye gelatinizes at a relatively low functions of carbohydrates and proteins. temperature, 55”-70°C, at which the activity of alpha-amylase is at a maximum. In order to avoid excessive amylolytic breakdown of the starch, a normal salt level is used for making rye soft bread, Soft bread Under certain conditions rye grains germinate and the pH of the dough is lowered by acid modifica- in the harvest field and then exhibit increased tion in a ‘sour dough’ process, preferably by lactic enzymic activity which may be undesirable for acid fermentation with species of Lactobacillus. 212 TECHNOLOGY OF CEREALS Straight dough process Yeast is Used for leavening' and the dough is acidified by adding lactic acid or acidic citrates. The dough is mixed slowly to prevent too much viscosity of the pentosans. All doughs containing rye flour have to be acidified because sour conditions improve the swelling power of the pentosans and also partly inactivate the amylase, which would otherwise have a detrimental effect on the baking process Briimmer, 1991). Conventional dough improvers are not widely used in making rye or rye/wheat bread. Instead, pregelatinized potato flour or maize starch or rice starch may be added at a level of 3% (on flour wt). These materials have high water-binding capacity and increase the water absorption of the dough. Other substances used with similar effect include hydrocolloids and polysaccharide gums such as locust bean and guar gums. Staling of rye bread is less serious than that of wheat bread, and shelf-life may be extended in various ways: by the addition of malt flour or pregelatinized potato flour or starch; by the use of sour dough; or by wrapping while still warm. Pumpernicke, Pumpernickel is a type of soft rye bread made from very coarse rye meal by a sour dough process. A very long baking time (18-36 h) is used, with a starting temperature of about 150°C being gradually lowered to about 110°C. Pumpernickel has a long shelf-life. Crispbread (Knackerbrot) Rye crispbread is generally made from rye wholemeal or flaked rye, using water or milk to mix the dough, and may be fermented with yeast (brown crispbread) or unfermented (white crisp- bread). The traditional method used in Sweden is to mix rye meal with snow or powdered ice; expansion of the small air bubbles in the ice-cold foam raises the dough when it is placed in the oven. It is desirable to use rye flour or meal of low alpha-amylase activity. In one process, a dough made from rye whole- meal, yeast, salt and water is fermented for 2-3 h at 24"-27°C. After fermentation, the dough is mixed for 5-6 min, proved for 30-60 min, sheeted, dusted with rye flour, and cut to make toughening that codd be caused by the high and impair normal crumb formation (Seibel and Sour-dough process Sour doughs, containing lactic acid bacteria, were probably in use for making bread as long ago as 1800 B.C. in Eastern Mediterranean regions, the process spreading to Germany between the 1st and 6th centuries A.D., where it was used mainly by monks and guilds (Seibel and Briimmer, 1991). The sour dough is a sponge-and-dough process. A starter dough is prepared by allowing a rye dough to stand at 24"-27"C for several hours to induce a natural lactic acid fermentation caused by grain micro-organisms. Alternatively, rye dough is inoculated with sour milk and rested for a few hours, after which a pure culture of organic acids (acetic, lactic, tartaric, citric, fumaric) is added to simulate the flavour of a normally soured dough. Part of the mature sour dough is retained as a subsequent starter, while the remainder is mixed with yeast and rye flour or rye wholemeal, or a blend of rye and wheat flours, and acts as a leavening agent in the making of rye sour bread (Drews and Seibel, 1976). The flavour of San Francisco sour dough bread is due largely to lactic and acetic acids which are produced from D-glucose by Lactobacillus, a bacterium active in sour dough starter. The starter is fermented for 2 h at 24"-26"C and then held in a retarder for 10 h at 3"-6"C. The dough, which incorporates 2-10% of starter (on flour wt basis) besides vital gluten (1-2%), shortening, yeast (2.5-4.0%), salt, sugar, yeast food and water, is fermented for 30-60 min, scaled, rested for 12-15 min, proved for 5-8 h, and baked (1 lb loaves) for 30-35 min at 204"-218"C. However, this long drawn-out process can be avoided by using commercially available free- flowing sour dough bases (Ziemke and Sanders, 1988; Seibel and Briimmer, 1991). BREAD-BAKING TECHNOLOGY 213 fermented for 3 hat 32°C. The rest ofthe triticale flour was then added, with salt, 1.5% on flour wt, and water, to give a dough yield of 160-165%, and then fermented for 30 min at 32°C. The loaves were baked at 235"-245"C (Haber and Lewczuk, 1988). Bread made from all-triticale flour stales more rapidly than all-wheat bread. Bread made from 5O:SO or 75:25 blends of triticale flour and wheat flour had higher specific volumes (4.8; 4.9 ml/g) than the bread baked from all wheat flour (4.4 ml/g); no deleterious effect on crumb characteristics, viz. grain and texture, resulted from the admixture of triticale flour (Bakhshi et al., 1989). Barley and oats During World War 11, when supplies of impor- ted wheat were restricted in Britain, the Govern- ment authorized the addition of variable quantities (up to 10% of the total grist in 1943) of barley, or of barley and oats, to the grist for making bread flour (cf. p. 93). For this purpose, the barley was generally blocked (cf. p. 162) to remove the husk, and the oats were used as dehusked groats (cf. p. 166). Good quality bread has been made in Norway from a blend of 50% of wheat flour of 78% extraction rate, 20% of barley flour of 60% extraction rate, and 30% of wheat wholemeal, using additional shortening (Magnus et al., 1987). For use in bakery foods in the U.S.A., cleaned oat grain is steam-heated to about 100°C and then held in silos to be 'ovenized' by its own heat for about 12 h. This process preserves the mineral and vitamin contents, and conditions the oats. The grain is then impact dehulled (cf. p. 167) without previous kilning (McKechnie, 1983). Rice Bread of acceptable quality has been made from a blend of 75 parts of wheat flour (12.1% protein content, 14% m.c. basis) with 25 parts of rice flour which had been partly gelatinized by extru- sion. The rice flour was milled from rice grits (7.32% protein content, 14% m.c. basis) which were pregelatinized to 76.8% by extrusion, using pieces about 7.6 X 7.6 cm (3 X 3 in) in size, which are baked for 10-12 min at 216"-249°C. The baked pieces are stacked on edge and dried in a drying tunnel for 2-3 hat 93"-104°C to reduce the moisture content to below 1%. Ryvita is a crisp bread made from lightly salted rye wholemeal. Flat breads A new type of crispbread product appeared in the 1990s under the trade name 'Cracotte', manu- factured from wheatflour by a continuous extru- sion cooking process. In this process the flour of about 16% m.c. is heated and sheared to form a fluid melt at 13O"-16O0C in which starch forms the continuous phase. After extrusion, it forms a continuous strip of expanded foam (specific volume 7-10 ml/g). Individual biscuits are cut from the strip and packed like crispbreads. This type of product, which has gained popularity in many countries, may be manufactured from any cereal type, and variations have appeared which included rye, rice and maize, either as the minor or major component in blends with wheat. Triticale The breadmaking characteristics of flour made from early strains of triticale were discouraging, although bread quality could be improved by addition of dough conditioners. However, bread of good quality has been made from recent triticale selections. Bread baked commercially with 65% of wheat flour blended with 35% of triticale stoneground wholemeal was first marketed (as 'tritibread') in the U.S.A. in 1974. Triticale flour has been tested extensively in Poland for breadmaking. The best results, using a blend of 90% triticale flour plus 10% of rye four, were obtained with a multi-phase (pre- ferment, sour-dough) process in which the pre- ferment was made with the rye flour (10% of the total flour) with water to a pre-ferment yield of 400%, and a fermentation time of 24 h at 28"-29"C. The sour used triticale flour (50% of the total flour) with 1-2% of yeast (on total flour basis) and water to give a sour yield of 200%. This was 214 TECHNOLOGY OF CEREALS a Creusot Loire BC-45 twin screw extruder. The beneficial effects of extrusion treatment appeared to be due to thermal modification of the starch in the rice flour (Sharma et al., 1988). The volume of loaves baked from this blend was below that of all-wheat flour loaves, but in other respects the bread was judged acceptable. The low contents of sodium, protein, fat and fibre and the high content of easily digested carbohydrate favour the use of rice bread as an alternative to wheat bread for persons suffering from inflamed kidneys, hypertension and coeliac disease (cf. p. 297). The volume of loaves of yeast-leavened bread made from 100% of rice flour is improved by the addition of hydroxypropylmethyl cellulose, a modifying the bread-making process. gum which creates a film with the flour and water that retains the leavening gases and allows expansion (Bean, 1986). Stabilized and extracted rice bran can provide nutritional fortification, when used at levels up to 15%, for bakery products such as yeast-raised goods, muffins, pancake mixes and biscuits. The rice bran contributes flavour, increases water absorption without loss of volume, adds sigmficant amounts of essential amino acids, vitamins and minerals, but does not affect mixing tolerance or fermentation. The blood cholesterol-lowering capabilities of rice bran are a further inducement for its use (Hargrove, 1990). Maize Maize flour is used to make bread of a sort in Latin America, and also for pancake mixes, infant foods, biscuits and wafers. Pregelatinized maize starch may be used as an ingredient in rye bread (cf. p. 212). Bread made with composite flour Flour milled from local crops can be added to wheat flour to extend the use of an imported wheat supply and thereby save the cost of foreign currency. This arrangement is particularly appro- priate for developing countries which do not grow wheat. Satisfactory bread can be made from such composite flour, viz. a blend of wheat flour with flour of other cereals such as maize, sorghum, millet or rice, or with flour from root crops such as cassava. The flour of the non-wheat component acts as a diluent, impairing the quality of the bread to an extent depending on the degree of substitution of the wheat flour. A higher level of substitution is possible with a strong wheat flour than with a weak one. Possible levels of substitution, as percentage by weight of the composite flour, are 15-20% for sorghum flour and millet flour, 20-25% for maize flour. Somewhat higher levels of substitution may be possible by the use of bread improvers or by A blend of 70% of wheat flour, 27% of rice flour and 3% of soya flour made acceptable bread, provided surfactant-type dough improvers were used. A more economical blend, producing accept- able bread, is 50% of wheat flour, 10% of rice flour and 40% of cassava flour. Rice starch can also be used, e.g. a blend of 25% of rice starch with 75% of wheat flour yielded acceptable bread (Bean and Nishita, 1985). Bread of acceptable quality is being made in Senegal and Sudan from a blend of 70% of imported wheat flour of 72% extraction rate and 30% of flour milled locally from white sorghum to an extraction rate of 72-75%. The water absorption of a blend of 15% of millet flour with 85% of wheat flour is about 3% higher than that of the wheat flour alone, and extra water must therefore be added. Acceptable bread can be made at an even higher rate of substitution, viz. 30%, by modifying the bread- making process in various ways, e.g. by delaying the addition of the millet flour until near the end of the mixing process; by the use of improvers, such as calcium stearoyl lactylates or tartaric esters of acetylated mono- and di-glycerides of stearic acid; or by increasing the addition of sugar and fat to 4% (each) on composite flour wt. When using a blend of maize flour and wheat flour to make bread it is desirable to increase the addition of water by about 2% for each 10% substitution of the wheat flour by maize flour, and to increase the amount of yeast to about 1.5 BREAD-BAKING TECHNOLOGY 21 5 cellulose, viz. a 1,Clinked beta-D-glucose polymer. 1% solutions are thixotropic, appearing gel-like at rest, but mixing, pouring, pumping easily (Anderson and Audon, 1988). Xanthan gum is already finding a use as a thickening agent in fast foods. To achieve the best results with sorghum flour, the xanthan gum should be soaked in water before incorporation in the dough to give the bread a more open structure, and salt should be added to improve the flavour of the bread. Sorghudxanthan bread retains its freshness for 1988). Yeasted rice flour breads, using 100% rice flour or 80% of rice flour plus 20% of potato starch, but withom any wheat flour, could be made if times that suitable for wheat flour alone. The use of hardened fat or margarine (2% on flour wt) is recommended to achieve good bread quality. Addition of emulsifiers, such as lecithin, stearates or stearoyl lactylates, is also recommended. Dried Distillers' Grains (DDG) This is a by-product in the production of distilled alcohol. During the fermentation of grains such as maize, rye, barley, the starch is products, while the nutrients, e.g. protein, fibre, fat, vitamins, minerals, remain in the residue and are concentrated three-fold in the DDG. DDG has potential for use in bread (at levels up to 15%) converted to alcohol, carbon dioxide and other at least Six daYs-longer than wheat bread (Satin, and other baked products. Addition of 10% of DDG to wheat flour raised the protein content from 15 to 17y0, and made a valuable contribu- the binding function of the wheat gluten was replaced by a gum - carboxy methyl cellulose (CMC) at a level of 1.6% on flour + starch basis, tion of amino acids such as threonine, serine, glutamic acid, alanine, methionine, leucine, histidine and lysine (Reddy et al., 1986). or hydroxy propyl methyl cellulose (HPMC) at a level of about 3% (on flour + starch basis). Bread made in this way met reference standards for wheat (white) bread for sp. vol., crumb and crust colour, Instron firmness and moisture content. The CMC or HPMC has the viscosity and film- forming characteristics to retain gas during proofing that are usually provided by gluten (Bean and Nishita, 1985; ylima& et al. , 1988). A mixture of galactomannans (hydrocolloids) a gluten substitute. A blend of three parts of and one part of tara seed flour, 75-100 pm particle size, was favoured, giving good volume yield, crumb structure and flavour (Jud and Brummer, 1990). The use of tara gum would not be permitted in the U.K., while carob and guar gums would be permitted only for coeliac sufferers. Another kind of gluten substitute, particularly for use in developing countries, can be made by boiling a 10% suspension of flour milled from tropical plants, e.g. cereal or root, in water until the starch gels, and then cooling. This material is then added to a blend of non-wheat flour, sugar, salt, yeast, vegetable oil, then mixed for 5 min, allowed to rise, and baked. The starch gel func- tions like gluten, trapping the gas evolved by yeast action (Anon., 1989). Soya bread A bread with good flavow, good storage proper- ties (up to two weeks) and a fine to medium crumb structure has been made from a b1end Of wheat 'Ontent Of 19" and a reduced carbohydrate diabetics (Anon., 1988a). flour with 3040% of soya flour. With a Protein from carob, guar and tars seed has been used as content, such bread is Particularly Suitable for carob seed flour (locust bean: Ceratonia siliqua) Bread made with gluten substitutes It is no longer true that wheat gluten is necessary to make white bread of good quality. Acceptable bread has been made from sorghum flour - without any wheat flour and therefore without gluten - by the use of a gluten substitute, xanthan gum, a water-soluble polymer of high viscosity, which functions in the same way as gluten. Xanthan gum is made by fermenting carbohydrates with a bacterium, Xanthomonas campestris. The resulting viscous broth is Pasteur- ized, precipitated with isopropyl alcohol, dried and ground. 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