Flour Quality Introduction Table 7. 1 shows typical proportions of flour streams e: In the milling of cereals by the gradual reduc. (expressed as percentages of the wheat)from well-equipped and well-adjusted mill in the U. K on system(see Ch 6), flour is produced by every making flours of fairly low ash yield. The ash machine in the break scratch and reduction systems of the normal mill-flow. The stock fed yield of the individual flour streams is also shown Flour streams with the lowest ash yield (e. g in terms of proportions of endosperm, embryo group l in Table 7. 1)may be described as'patent and bran contained in it, and the region of the four. Those from the end of the milling process grain from which the endosperm is derived with high ash yield are called 'low-grade' in the and each machine flour is correspondingly distinc- TABLE 7.1 tive in respect of baking quality, colour and Typical Proportions and Ash Yields of Flour Streams granularity, contents of fibre and nutrients, and the amount of ash it yields upon incineration Proportions Ash yield ( of feed(%, d.m.) By far the most abundant four consumed in Flour streams to I Bk the industrialized world is derived from wheat because of this, and the unique versatility ofGroup 1:High Grade 12.0-21.00.350.38 wheaten flour, the majority of this chapter is devoted to it. flours from other cereals are ABC 14.0-17 70-100.380.47 35400.350 given some In the U.K. today there are no recognized Group 2: Middle Grade 2.5-7.50.390.70 standards for flour grades: each miller makes his E grades according to customers requirements, and 1.3-3.00.75-1,47 exercises his skill in maintaining regularity of 1.5-2.50.500.72 II Bk 1.5-3.00.53-0 quality for any particular grade iiI Bk bran finisher four 0.02.50.70-1,00 0.00.70.700.90 I Bk Coarse Midds 3.06.00.500.82 Flour grades II Bk Coarse Midd 1.5-3.50.700 25-300.700.80 If the flour streams from all the machines in Group 3: Low grade the break, scratch and reduction systems are B2 blended together in their rational proportions,F 1.2-2.50.40-0.45 0.7-1.20.58-1.3 the resulting four is known as ' straight-run H 0.61.2 grade. Other grades are produced by selecting 0.5-0.70.882.25 and blending particular four streams, frequently IV Bk finisher flour 0.0-1.01.50-2.0 on the basis of their ash yield or grade colour Total group 3 80-2. measures of their non-endosperm tissue content)
7 Flour Quality Introduction Table 7.1 shows typical proportions of flour streams (expressed as percentages of the wheat) from a well-equipped and well-adjusted mill in the U.K. yield of the individual flour streams is also shown. Flour streams with the lowest ash yield (e.g. group 1 in Table 7.1) may be described as ‘patent’ flour. Those from the end of the milling process In the milling of cereals by the gradual reducmachine in the break, scratch and reduction systems of the normal mill-flow. The stock fed to each grinding stage is distinctive in composition - in terms of proportions of endosperm, embryo grain from which the endosperm is derived - and each machine flour is correspondingly distinctive in respect of baking quality, colour and granularity, contents of fibre and nutrients, and the amount of ash it yields upon incineration. By far the most abundant flour consumed in the industrialized world is derived from wheat; because of this, and the unique versatility of wheaten flour, the majority of this chapter is ti’n system (see Ch’ 6), flour is produced by every making flours of fairly low ash yield. The ash and bran contained in it, and the region of the with high ash yield are called ~l~~-~~~d~’ in the TABLE 7.1 Typical Proportions and Ash Yields of Flour Streams Proportions Ash yield (% of feed (%, d.m.) Flour streams Group 1: High Grade to I Bk) A 12 .O-2 1.0 0.35-0.38 B 14.0-17.0 0.35-0.38 C 7.0-10 0.38-0.47 3540 0.35-0.40 devoted to it. Flours from other cereals are however given some consideration. In the U.K. today there are no recognized Total group 1 Group 2: Middle Grade D 2.5-7.5 0.39-0.70 standards for flour grades: each miller makes his E 1.7-2.1 0.45-0.89 grades according to customer’s requirements, and G 1.3-3.0 0.75-1.47 I Bk 1.5-2.5 0.50-0.72 II Bk quality for any particular grade. I11 Bk 0.0-1.5 0.70-1.00 I11 Bk bran finisher flour 0.0-2.5 0.70-1.00 X (Scratch) 0.0-0.7 0.70-0.90 I Bk Coarse Midds 3.0-6.0 0.50-0.82 Flour grades I1 Bk Coarse Midds 1.5-3.5 0.70-0.84 1.5-3.0 0.53-0.69 exercises his skill in maintaining regularity of Total Group 2 25-30 0.70-0.80 If the flour streams from all the machines in Group 3: Low grade the break, scratch and reduction systems are B2 1.2-2.5 0.40-0.45 the resulting flour is known as ‘straight-run H 0.6-1.2 0.60-1.53 0.5-0.7 0.88-2.25 2.04.0 1.00-2.00 and blending particular flour streams, frequently IV Bk finisher flour 0.0-1.0 1.50-2.00 0.0-1.0 1.00-2.50 8-10 1.80-2.3 blended together in their rational proportions, F 0.7-1.2 0.58-1.35 J Iv Bk v Bk grade’. Other grades are produced by selecting on the basis of their ash yield or grade colour (measures of their non-endosperm tissue content). Total Group 3 170
FLOUR QUALITY 171 U. K. or 'clear'flour in the U.S.A. Clear four is replaced chlorine in 1922 as an improving and used industrially in the U. S A for the manufac- bleaching agent for breadmaking four because ture of alcohol, gluten, starch and adhesives(see was much more effective. Its use was discontinued Ch.15) in the u.s.a. in 1949 and in the u.k. from the end of 1955, after it had been shown by Mellanby Treatments of wheat flour (1946) that flour treated with Agene in large doses ht cause le hysteria (although Agene- treated four has never been shown to be harmful ng to human health). Nitrogen trichloride reacts Flour contains a yellowish pigment, of which with the amino acid methionine, present in wheat about 95% consists of xanthophyll or its esters, protein, to form a toxic derivative, methionine and has no nutritional significance. Bleaching of sulphoximine( bentley et al., 1950). the natural pigment of wheat endosperm by oxidation occurs rapidly when flour is exposed the atmosphere, more slowly when flour is stored Chlorine dioxide in bulk and by chemical Chlorine dioxide(CIO2), known as 'Dyox',is treatment. The principal agents used, or formerly now the most widely used improving and bleaching used, for bleaching four are nitrogen peroxide, agent in the U. K, the u.s.A. Australia and chlori hlorine dioxide, nitrogen trichloride, Canada. It was first used for these purposes in nzoyl peroxide and acetone peroxide 1949 in the U.s.A. and in the u. K. in 1955. The gas is produced by passing chlorine gas through Nitrogen peroxide (NO2) an aqueous solution of sodium chlorite. Dyox gas contains a maximum of 4%CIO. The chlorine NO2 produced by a chemical reaction or by dioxide gas is released by passing air through the the electric arc process was widely used as a solution, and is applied to breadmaking flour at bleaching agent in the early twentieth century. a rate of 12-24 mg/kg (it is permitted in the U. K Its use has been discontinued except in the u.s.a up to 30 mg/kg). Chlorine dioxide treatment of and Australia, where it is still legally permitted. flour destroys the tocopherols(cf Ch. 14). The use of chlorine dioxide is also permitted in Japan Chlorine The use of chlorine gas(Cl2) for treatment of Benzoyl peroxide cake four(except wholemeal) is permitted in the (C6 CO)2O2 or BzO2 is a solid bleaching U.K. to a maximum of 2500 mg/kg. The chlorine agent which was first used in 1921. It is supplied modifies the properties of the starch for high- as a mixture with inert, inorganic fillers such as ratio cake flour (cf p. 178). For cake flours the CaHPO4, Ca3(PO4)2, sodium aluminium sulphate usual level of treatment is 1000-1800 mg/kg. The or chalk Novadelox, a proprietary mixture, con Bread and Flour Regulations 1984 do not permit tains up to 32% of benzoyl peroxide but 16% is its use in bread flour in the U. K. The use of the usual proportion. The dosage rate, normally chlorine is not permitted in most European 45-50 mg/kg, is restricted to 50 mg/kg in the countries, but it is allowed in four for all purposes U. K. by the Bread and Flour regulations 1984 in the u.s.A., Canada, Australia, New Zealand The bleaching action occurs within about 48 h (to 1500 mg/kg)and South Africa(to 2500mg/kg) his bleacher has the advantage over gaseous agents that only a simple feeder is required, and Nitrogen trichloride storage of chemicals presents no hazard; the fact that it has no improving action is advantageous This gas(NCl3), known as 'Agene,, was patented in the bleaching of patent fours. The treated flour s a four bleach by j. C. Baker in 1921, and contains traces of benzoic acid but objection has
FLOUR QUALITY 171 replaced chlorine in 1922 as an improving and bleaching agent for breadmaking flour because it was much more effective. Its use was discontinued in the U.S.A. in 1949 and in the U.K. from the end of 1955, after it had been shown by Mellanby (1946) that flour treated with Agene in large doses might cause canine hysteria (although Agenetreated flour has never been shown to be harmful to human health). Nitrogen trichloride reacts with the amino acid methionine, present in wheat protein, to form a toxic derivative, methionine sulphoximine (Bentley et al., 1950). Chlorine dioxide Chlorine dioxide (C102), known as ‘Dyox’, is now the most widely used improving and bleaching agent in the U.K., the U.S.A., Australia and Canada. It was first used for these purposes in 1949 in the U.S.A. and in the U.K. in 1955. The gas is produced by passing chlorine gas through an aqueous solution of sodium chlorite. Dyox gas contains a maximum of 4% C102. The chlorine dioxide gas is released by passing air through the solution, and is applied to breadmaking flour at a rate of 12-24 mg/kg (it is permitted in the U.K. up to 30 mg/kg). Chlorine dioxide treatment of flour destroys the tocopherols (cf. Ch. 14). The use of chlorine dioxide is also permitted in Japan. Benzoyl peroxide (C6H5C0)202 or Bz02 is a solid bleaching agent which was first used in 1921. It is supplied as a mixture with inert, inorganic fillers such as CaHP04, Ca3(P04)2, sodium aluminium sulphate or chalk. Novadelox, a proprietary mixture, contains up to 32% of benzoyl peroxide but 16% is the usual proportion. The dosage rate, normally 45-50 mg/kg, is restricted to 50 mg/kg in the U.K. by the Bread and Flour Regulations 1984. The bleaching action occurs within about 48 h. This bleacher has the advantage over gaseous agents that only a simple feeder is required, and storage of chemicals presents no hazard; the fact that it has no improving action is advantageous in the bleaching of patent flours. The treated flour contains traces of benzoic acid, but objection has U.K. or ‘clear’ flour in the U.S.A. Clear flour is used industrially in the U.S.A. for the manufacture of alcohol, gluten, starch and adhesives (see Ch. 15). Treatments of wheat flour Bleaching Flour contains a yellowish pigment, of which about 95% consists of xanthophyll or its esters, and has no nutritional significance. Bleaching of the natural pigment of wheat endosperm by oxidation occurs rapidly when flour is exposed to the atmosphere, more slowly when flour is stored in bulk, and can be accelerated by chemical treatment. The principal agents used, or formerly used, for bleaching flour are nitrogen peroxide, chlorine, chlorine dioxide, nitrogen trichloride, benzoyl peroxide and acetone peroxide. Nitrogen peroxide (NO,) NO2 produced by a chemical reaction or by the electric arc process was widely used as a bleaching agent in the early twentieth century. Its use has been discontinued except in the U.S.A and Australia, where it is still legally permitted. Chlorine The use of chlorine gas (C12) for treatment of cake flour (except wholemeal) is permitted in the U.K. to a maximum of 2500 mg/kg. The chlorine modifies the properties of the starch for highratio cake flour (cf p. 178). For cake flours the usual level of treatment is 1000-1800 mg/kg. The Bread and Flour Regulations 1984 do not permit its use in bread flour in the U.K. The use of chlorine is not permitted in most European countries, but it is allowed in flour for all purposes in the U.S.A., Canada, Australia, New Zealand (to 1500 mg/kg) and South Africa (to 2500mg/kg). Nitrogen trichloride This gas (NC13), known as ‘Agene’, was patented as a flour bleach by J. C. Baker in 1921, and
172 TECHNOLOGY OF CEREALS not been raised BzO2 is also used in New South flours(those nearer the tail end of the break and Wales, Queensland, the U.SA, Canada, the reduction systems) in general requiring more Netherlands, New Zealand (up to 40 mg/kg, for treatment than the patent flours(cf. p. 170). It pastry four only) and Japan(up to 300 mg/kg). is therefore customary to group the machine fours according to quality into three or four Acetone peroxide streams for treatment. a possible grouping is indicated in Table 7. I Each group would be given Acetone peroxide is a dry powder bleaching appropriate bleacher treatment: e. g. the lowest nd improving agent, marketed as'Keetox',a 20% of flour might receive treatment at ten times blend of acetone peroxides with a diluent such as the rate for the best quality 50%. The final grades dicalcium phosphate or starch. The concentration are then made up by blending two or more of the in terms of H2o2 equivalent per 100 g of additive groups in desirable proportions. plus carrier is 3-10 for maturing and bleaching or0.75 for use in doughmaking. Its use has been Flours for various purposes permitted in the U.S.A. since 1961, and also in Canada, but it is not, as yet, permitted in the Wheat flour is used for making foc U. K. It is used either alone or in combination of widely varying moisture content(see Table 7.3) with benzoyl peroxide. The usual dosage rate is 446 mg/kg on flour basis. Significant dates in TABLE 7. 3 Flour-based products and their me history of flour bleaching are summarized Table 7. 2 Moisture content Type of product Range Mean Moisture level Flour blending for bleaching treatment Because the various flour streams differ in their Puddings 1367 Medium characteristics, the optimum level of bleaching 35-40 Mediurn 、 treatment varies correspondingly, the lower grade Pastry Biscuits(cookies, crackers) 1-6 TABLE 7.2 Significant Dates in the History of Flour bleaching Data extracted from McCance and Widdowson(1967) 1901 Andrews patents flour treatment with NO,(chemical The proportions in which the various ingredients of baked products are present in the recipe 1903 Alsop patents flour treatment with NOz(electrical relative to flour(100 parts), are shown in Table 909 NO, in us 7. 4. Biscuit dough is stiff to permit rolling and 1911 Keswick Convention- unmarked flour to be flattening; bread dough is a plastic mass that can 1921 Benzoyl per be moulded and shaped wafer batter is a liquid Ispension that will flow through a pipe 1922 NCl, replaces Cl as bleacher for breadmaking flour 1923 Committee appointed to inquire into use of For comparison with products listed in Tal reservatives and colouring matter in 7. 4, a typical wholemeal wheat extruded snack 1924 Committee's activities extended to chemi formulation would contain the following amounts 1927 Committee reported that bleaching of ingredients, in relation to 100 g white four: 7 g agents were in use, and that Cl, N soya protein, 14 g wheat bran, 1.4 g oil, 0.4 emulsifier, 23 g water, 7 g sugar, 2 g salt, 2 g 1949 C1O, first used in the U. S. A dicalcium phosphate, 3.6 g milk powder(Guy U 993). the U.K 1961 Acetone peroxide permitted in the U.S.A(not in the products, as purchased or as consumed, is shown in Table 7.5
172 TECHNOLOGY OF CEREALS not been raised. Bz02 is also used in New South flours (those nearer the tail end of the break and Wales, Queensland, the U. S.A, Canada, the reduction systems) in general requiring more Netherlands, New Zealand (up to 40 mg/kg, for treatment than the patent flours (cf. p. 170). It pastry flour only) and Japan (up to 300 mg/kg). is therefore customary to group the machine flours according to quality into three or four streams for treatment. A possible grouping is indicated in Table 7.1 Each group would be given Acetone peroxide Acetone peroxide is a dry powder bleaching appropriate bleacher treatment: e.g. the lowest and improving agent, marketed as ‘Keetox’, a 20% of flour might receive treatment at ten times blend of acetone peroxides with a diluent such as the rate for the best quality 50%. The final grades dicalcium phosphate or starch. The concentration are then made up by blending two or more of the in terms of H202 equivalent per 100 g of additive groups in desirable proportions. plus carrier is 3-10 for maturing and bleaching, or 0.75 for use in doughmaking. Its use has been permitted in the U.S.A. since 1961, and also in Canada, but it is not, as yet, permitted in the with benzoyl peroxide. The usual dosage rate is 446 mg/kg on flour basis. Significant dates in the history of flour bleaching are summarized in Table 7.2. Moisture content Flours for various purposes Wheat flour is used for making food products U.K. It is used either alone or in combination of widely varying moisture content (see Table 7.3). TABLE 7.3 Flour-based Products and their Moisture Contents Type of product Range Mean Moisture (Yo) (”/.I level Flour blending for bleaching treatment soup 78-80 85 High 13-67 45 Medium 3540 38 Medium characteristics, the optimum level of bleaching Cakes 5-30 17 Medium Because the various flour streams differ in their Puddings Bread treatment varies correspondingly, the lower grade Pastry 7 Low Biscuits (cookies, crackers) 1-6 5 Low Data extracted from McCance and Widdowson (1967). The proportions in which the various ingredients of baked products are present in the recipe, relative to flour (100 parts), are shown in Table 7.4. Biscuit dough is stiff to permit rolling and flattening; bread dough is a plastic mass that can be moulded and shaped; wafer batter is a liquid suspension that will flow through a pipe. For comparison with products listed in Table 7.4, a typical wholemeal wheat extruded snack formulation would contain the following amounts of ingredients, in relation to 100 g white flour: 7 g soya protein, l4 g wheat bran, ’ *4 g Oil, Oe4 g emulsifier, 23 g water, 7 g sugar, 2 g salt, 2 g dicalcium phosphate, 3.6 g milk powder (Guy, 1993). The flour content of various flour-containing products, as purchased or as consumed, is shown in Table 7.5. TABLE 7.2 Significant Dates in the History of Flour Bleaching 1901 Andrews patents flour treatment with NO2 (chemical process) 1903 Alsop patents flour treatment with NOZ (electrical treatment) 1909 NO2 in use 1911 Keswick Convention - unmarked flour to be 1921 Benzoyl peroxide first used 1921 J. C. Baker patents NC13 as flour bleacher 1922 NC13 replaces Cl as bleacher for breadmaking flour 1923 Committee appointed to inquire into use of 1924 Committee’s activities extended to chemical 1927 Committee reported that bleaching and improving 1949 NC13 use discontinued in the U.S.A. 1949 C102 first used in the U.S.A. 1955 NC13 use discontinued in the U.K. 1955 C102 first used in the U.K. 1961 Acetone peroxide permitted in the U.S.A. (not in the unbleached preservatives and colouring matter in food substances for flour treatment agents were in use, and that C1, NCI3 and Bz02 were not among those least open to objection U.K.)
FLOUR QUALITY 173 ABLE 7. 4 Proportions of Constituents in recipes for Baked Productss(Relative to Flour: 100 Parts) Type of product Water powder Sugar 1.8 12.5 0.1-2.0 Steak and kidney pudding 0.7 Puff 0.7 Hard sweet 72 0.7 0.5 204 High ratio Wafer batter 3 0.2 0.3 t long Fermentation t mixtures of sodium and ammonium carbonate or bicarbonate S Source: FMBRA. TABLE 7.5 moisture contents(at least 7% and not more than Flour Content of flour-Based Foods, as Purchased or 15.5%, respectively), fat acidity, particle size (98% through a 212 Hm sieve) and protocol Parts of for ash determination. Optional ingredients and Food product per 100 approved additives are listed flour In the U. K, four for human consumption should conform with the nutritional requirements set out in the Bread and Flour Regulations 1984 seml-sweet 67-82 135(cf.p.293) ginger nu For each purpose, flour with particular proper Short pastry 608065155 ties is required: these are secured, in the first ns, scones, teacakes 220 place, by choice of an appropriate wheat grist in terms of strong and weak wheats. The average 84630330 Puddings composition of wheat grists used for milling flour Source: FMBRA Flour wt at natural m.c. Product wt Table 4.8 Table 4.8 also shows that, of the total flour milled in the u.K. in 1990/91, 63% was used for bread, 15% for biscuits, 6% for house- The Codex Alimentarius Commission of the hold use, 2% for cakes, 2% for starch manufacture United Nations Food and Agriculture Organiza- and 12% for other products tion issued standard 152 on flour for human 'Other'food products made with wheat flour consumption in 1985. It defines acceptable sources include pastry, meat pies, sausages, sausage rolls as Triticum aestivum L. bread wheat, and T. rusks, pet foods, baby foods, invalid foods compactum club wheat, the required protein and chapatties, buns, scones, teacakes, pizzas, soups
FLOUR QUALITY 173 TABLE 7.4 Proportions of Constituents in Recipes for Baked Products§ (Relative to Flour: 100 Parts) Constituents Type of product Whole Raising Milk Water Fat Salt egg agent powder Sugar Yeasted products (Yeast) Bread, CBP* 61 0.7 1.8 1.8 Bread, LFPt 57 0.7 1.8 1.1 Cream crackers 32 12.5 1.0 0.1-2.0 Short 25 50 2.0 Pie 31 43 2.0 Steak and kidney pudding 30-36 50 0.7 Puff 40-50 50-70 0.7 Choux 125 50 150 Hard sweet 20 17 0.7 1.1* 2.6 22 Soft 10 32 0.1 0.5$ 2.0 30 Plain 50 40 35 3.5* 40 Pastry Biscuits (whey) Cake High ratio 70 65 2.0 60 5.0* 8 120 Sponge 1.0 170 100 Wafer batter 150 3 0.2 0.3$ * Chorleywood Bread Process. t Long Fermentation Processes. $ Mixtures of sodium and ammonium carbonate or bicarbonate. 5 Source: FMBRA. TABLE 7.5 Flour Content of Flour-Based Foods, as Purchased or Consumed* moisture contents (at least 7% and not more than 15.5%, respectively), fat acidity, particle size (98% through a 212 pm sieve) and protocol for ash determination. Optional ingredients and approved additives are listed. (%) (%) ptflour In the U.K., flour for human consumption should conform with the nutritional requirements - ‘12 90 set out in the Bread and Flour Regulations 1984 semi-sweet 67-82 74 135 (cf. P. 293). ginger nut 43-57 49 205 For each purpose, flour with particular proper- 60-80 65 155 ties is required: these are secured, in the first Bread Short pastry Buns, scones, teacakes 3657 45 220 place, by choice of an appropriate wheat grist in Cakes, pastries, choc. wafer 23-40 33 300 terms of strong and weak wheats. The average uo 25 4oo composition of wheat grists used for milling flour Biscuits (chocolate) Puddings for various purposes in the U.K. is shown in flour milled in the U.K. in 1990/91, 63% was at m.c. of final product. used for bread, 15% for biscuits, 6% for houseThe Codex Alimentarius Commission of the hold use, 2% for cakes, 2% for starch manufacture United Nations Food and Agriculture Organiza- and 12% for ‘other products’. tion issued standard 152 on flour for human ‘Other’ food products made with wheat flour consumption in 1985. It defines acceptable sources include pastry, meat pies, sausages, sausage rolls, as Triticum aestivum L. bread wheat, and T. rusks, pet foods, baby foods, invalid foods, compactum club wheat, the required protein and chapatties, buns, scones, teacakes, pizzas, soups Parts of F1our ‘Ontent product Food product Range Mean per 100 Crispbread Biscuit 53-72 70 145 846 30 330 * Source: FMBU. Flour wt at natural m.c. Product Wt Table 4.8. Table 4.8 also shows that, of the total
174 TECHNOLOGY OF CEREALS frying, chocolate and, quorice, batter(for fish rapidly if the flour is exposed to the action of the ( Ch. 13), premixes, sugar confectionery, cereal air. During such aerated storage, fat acidity convenience foods, snack foods, breakfast cereals, increases at first, owing to lipolytic activity, and puddings, gravy powder, blancmange and brewing later decreases, by lipoxidase action; products of adjunct. Specific requirements for flours for various the oxidation of fatty acids appear; the proportion purposes are outlined below. of linoleic and linolenic acids in the lipids falls; and disulphide bonds(-S-S-)decrease in number. Bread four The change in baking quality, known as matura tion,or ageing,, can be accelerated by chemical The predominance of wheat flour for making improvers,, which modify the physical properties aerated bread is due to the properties of its protein of gluten during fermentation in a way that results which,when the four is mixed with water, forms in bread of better quality being obtained. Matured in elastic substance called gluten(cf. Chs 3 and flour differs from freshly milled flour in that it 8). This property is found to a slight extent in has better handling properties, increased tolerance rye but not in other cereals in the dough to varied conditions of fermentation The property of producing a loaf of relatively and in producing loaves of larger volume and large volume, with regular, finely vesiculated more finely textured crumb crumb structure, is possessed by flours milled Improving agents permitted in the U. K. Bread from wheats described as'strong'(cf Chs 4 and and Flour Regulations 1984(SI1984, No 1304), as 8). Protein strength is an inherent characteristic, amended by the Potassium Bromate(prohibitic but the amount of protein present can be influenced as a Flour Improver)Regulations 1990(SI 1990 by the conditions under which wheats are grow No. 399)are chlorine,(for cake flour only; not Protein content is also an important determinant wholemeal), cysteine hydrochloride(920)(all of bread quality, there being a positive correlation flour except wholemeal), chlorine dioxide (all between loaf specific volume(ml/g) and the flour except wholemeal), L-ascorbic acid(vitamin percentage of protein present C)(all flour except wholemeal; all bread), and Typical characteristics of Chorleywood Bread azodicarbonamide(all four except wholemeal Process(CBP)four, Bakers'flour(as used in Besides their improving effect, these substances the bulk fermentation process), and rollermilled give a whitened appearance to the loaf because wholemeal in the U.K. are shown in Table 7.6. of their beneficial effect on the texture of the crumb. Improving agents do not increase the Maturing and improving agen carbon dioxide production in a fermented dough, but they improve gas retention(because the The breadmaking quality of milled dough is made more elastic) and this results in flour tends to improve during storage for a period increased loaf volume(cf. Ch. 8) of 1-2 months. The improvement occurs more TABLE 7.6 Redox improvers Typical U. K. Bread Flour Analysis 1992 The action of improvers is believed to be an cBP Bakers'Wholemeal oxidation of the cysteine sulphydryl or thiol Moisture 1 6% 14 5% 14.6% (-SH) groups present in wheat gluten As a result, 14.7% these thiol groups are no longer available for grade colour participation in exchange reactions with disulphide 2FU 2IFU (S-S-)bonds-a reaction which is conside ed to 34FU release the stresses in dough -and consequently Water absorption 60.2% 62.0% 70 2% the dough tightens, i. e the extensibility is reduced Farrand units, (includes fungal enzyme Alternatively, it has been suggested that the oxidation of- sh groups may lead to the formation
174 TECHNOLOGY (Ch. 13), premixes, liquorice, batter (for fish frying), chocolate and sugar confectionery , cereal convenience foods, snack foods, breakfast cereals, puddings, gravy powder, blancmange and brewing adjunct. Specific requirements for flours for various purposes are outlined below. Bread flour The predominance of wheat flour for making aerated bread is due to the properties of its protein which, when the flour is mixed with water, forms an elastic substance called gluten (cf. Chs 3 and 8). This property is found to a slight extent in rye but not in other cereals. The property of producing a loaf of relatively large volume, with regular, finely vesiculated crumb structure, is possessed by flours milled from wheats described as 'strong' (cf. Chs 4 and 8). Protein strength is an inherent characteristic, but the amount of protein present can be influenced by the conditions under which wheats are grown. Protein content is also an important determinant of bread quality, there being a positive correlation between loaf specific volume (ml/g) and the percentage of protein present. Typical characteristics of Chorleywood Bread Process (CBP) flour, Bakers' flour (as used in the bulk fermentation process), and rollermilled wholemeal in the U .K. are shown in Table 7.6. Maturing and improving agents The breadmaking quality of freshly milled flour tends to improve during storage for a period of 1-2 months. The improvement occurs more TABLE 7.6 Typical U.K. Bread Flour Analysis 1992 Redox improvers The action of improvers is believed to be an oxidation of the cysteine sulphydryl or thiol ( -8H) groups present in wheat gluten. As a result, these thiol groups are no longer available for participation in exchange reactions with disulphide ( -8-8- ) bonds -a reaction which is considered to release the stresses in dough -and consequently the dough tightens, i.e. the extensibility is reduced. Alternatively, it has been suggested that the oxidation of -8H groups may lead to the formation CBP Bakers' Wholemeal 14.6% 11.0% 2.1 329 lSFU 30FU 60.2% 14.5% 12.1% 2.2 334 22FU 34FU 62.0% 14.6% 14.7% Moisture Protein Grade colour Falling number alpha-Amylase* Starch damage Water absorption 330 21FU 70.2% * Farrand units, (includes fungal enzyme). Source: FMBRA. OF CEREALS rapidly if the flour is exposed to the action of the air. During such aerated storage, fat acidity increases at first, owing to lipolytic activity, and later decreases, by lipoxidase action; products of the oxidation of fatty acids appear; the proportion of linoleic and linolenic acids in the lipids falls; and disulphide bonds ( -S-S- ) decrease in number . The change in baking quality , known as maturation, or 'ageing', can be accelerated by chemical 'improvers', which modify the physical properties of gluten during fermentation in a way that results in bread of better quality being obtained. Matured flour differs from freshly milled flour in that it has better handling properties, increased tolerance in the dough to varied conditions of fermentation and in producing loaves of larger volume and more finely textured crumb. Improving agents permitted in the U .K. Bread and Flour Regulations 1984 (SI1984, No.1304), as amended by the Potassium Bromate (Prohibition as a Flour Improver) Regulations 1990 (SI 1990, No.399) are chlorine, (for cake flour only; not wholemeal), cysteine hydrochloride (920) (all flour except wholemeal), chlorine dioxide (all flour except wholemeal), L-ascorbic acid (vitamin C) (all flour except wholemeal; all bread), and azodicarbonamide (all flour except wholemeal). Besides their improving effect, these substances give a whitened appearance to the loaf because of their beneficial effect on the texture of the crumb. Improving agents do not increase the carbon dioxide production in a fermented dough, but they improve gas retention (because the dough is made more elastic) and this results in increased loaf volume (cf. Ch. 8)