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 reduc- machine 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 distinc- tive 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 2.5-7.5 0.39-0.70 D 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 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 Agene- treated 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, con- tains 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 manufac- ture 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 high- ratio 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. 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 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 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 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 (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 Bakers' WholemealCBP 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 matura- tion, 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). FLOUR QUALITY 175 of new -S-S- bonds which would have the effect the total Br content of the bread to about 18 of increasing dough rigidity (cf. Ch. 3). mg/kg. Potassium bromate (KBr03) has never been Use of potassium bromate is permitted to 75 allowed in many European countries; it was mg/kg in the U.S.A.; to 50 mg/kg in Canada, specifically excluded from the list of permitted Sweden; to 40 mg/kg in the Soviet Union; and in additives in the U.K. by the Potassium Bromate Eire to about 18 mg/kg. KBr03 is not allowed in (Prohibition as a Flour Improver) Regulations the Netherlands or Australia. The greatest need for 1990 giving rise to considerable initial difficulties bromate occurs in continuous-mix baking, no-time in the baking industry. The changes in the use doughs, frozen doughs, and overnight sponges, of oxidizing improvers, consequent upon the as used in Cuba and other LatdAmerican coun- deletion of potassium bromate, are considered in tries. The typical level of addition in these types Ch. 8 (p. 201). Its use has also been voluntarily of baking approaches the 75 mg/kg maximum. discontinued in Japan and it is now little used in (Ranum, 1992). New Zealand. Hazards associated with potassium L-Ascorbic acid (vitamin C), E300, was first bromate include the fact that, as a strong oxidizing used as a bread improver by Jgrgensen in 1935. agent, it can cause fire or explosions. It is also It is now used for this purpose in the U.K., most toxic and there is strong evidence for its carcino- European countries and elsewhere, particularly genicity . At normal levels of addition however, in mechanical development processes of bread- it is not considered to persist at a significant level, making, such as the Chorleywood Breadmaking into the baked product, when used at permitted Process. The volume increase resulting from use levels. of ascorbic acid is generally less than that obtained Potassium bromate remains in use in the U.S.A. with equivalent weight of potassium bromate, although an agreement exists between Government and it is more costly. The improving effect of and users to reduce usage to a minimum. Although ascorbic acid is mediated by enzymes present in permitted in Canada, its use has declined in recent the flour. The functional form is the oxidized years in that country (Ranum, 1992). It has been form dehydroascorbic acid (DHA), which is used commercially as a bread improver since highly effective but cannot be used directly as it 1923. The rate of treatment is 10-45 mg/kg on is unstable. Ascorbic acid is oxidized to DHA flour weight. The substance acts as an oxidizing through catalytic action of ascorbic acid oxidase. agent after the flour has been made into a dough; Injection of oxygen during mixing hastens the it increases the elasticity and reduces the extens- oxidation, making ascorbic acid more effective ibility of the gluten. Treatment with bromate has (Chamberlain and Collins, 1977). The oxidation a similar action to that of ageing or maturing the to DHA is improved if the head space of the flour, and enables large bakeries to use a constant mixing machine contains an oxygen-enhanced fermentation period. atmosphere, e.g. a 5050 mixture of oxygen Potassium bromate is added to flour after being and air, equivalent to a mixture of 60% oxygen suitably diluted with an inert filler such as calcium plus 40% nitrogen (Ch. 8). Under these circum- carbonate or calcium sulphate. Proprietary brands stances, ascorbic acid alone is as effective an of improver contain 6, 10,25 or 90% of potassium oxidizing agent as is a combination of ascorbic bromate. The 6% brand is added at the rate of acid and potassium bromate used when the dough 0.022%. Higher levels of potassium bromate are is mixed under partial vacuum. An enzyme ‘DHA used in chemical dough development processes reductase’ is required for oxidation of sulphydryl (cf. Ch. 8). (-SH) compounds by DHA. Since untreated flour contains 1-8 mg/kg of Ascorbic acid strengthens the gluten; gas reten- bromine (Br), the bread made with untreated tion is thus improved and loaf volume augmented. flour contains 0.7-5.6 mg/kg of natural Br. Flour Ascorbic acid does not hasten proving. The treatment with 45 mg/kg of bromate leaves a maximum permitted levels (1989) are 50 mg/kg residue of 15 mg/kg of Br in the loaf, increasing in Belgium and Luxembourg, 100 mg/kg in the 176 TECHNOLOGY OF CEREALS Netherlands, 200 mg/kg in Canada, Denmark, other than wholemeal; higher levels (up to Italy, Spain, the U.S.A. and the U.K., 300 mg/kg 300 mg/kg) are permitted in certain biscuit flours. in France. No maximum level is specified in Use of L-cysteine is permitted in Denmark (up Australia, Greece, Portugal, Germany since to 25 mg/kg), Germany (up to 30 mg/kg), Belgium ascorbic acid is reckoned to be quite safe, although (up to 50 mg/kg), Australia, New Zealand and it is under scrutiny by the COT. Use of ascorbic the Netherlands (up to 75 mg/kg), Canada (up to acid is also permitted in Japan, New Zealand and 90 mg/kg) and Sweden (up to 100 mg/kg). Sweden. L-Cysteine is not mentioned as a permitted addi- Azodicarbonamide (1,l ’azobisformamide; tive in France, Greece, Italy, Luxembourg, NH2CONNCONH2; ‘ADA’) is a flour maturing Portugal, Spain or the U.S.A. agent, marketed as ‘Maturox’, or ‘Genitron’, or Cysteine accelerates reactions within and as ‘ADA 20%’ (‘AK20’). ‘Maturox’ contains between molecules in the dough which lead to an either 10% or 20% of ADA; ‘Genitron’ contains improvement in its viscoelastic and gas-holding 20% or 50% of ADA, dispersed in an excipient, properties. These reactions normally take place generally calcium sulphate and magnesium car- slowly during bulk fermentation but with the bonate. The particle size of ADA is generally 3- addition of cysteine the bulk fermentation period 5 pm. It was first used in the U.S.A. in 1962 can be eliminated. Cysteine, which is a rapid- (maximum permitted level 45 mg/kg on flour acting reducing agent, is used in the ADD in weight). When mixed into doughs it oxidizes the conjunction with slow-acting oxidizing agents, sulphydryl (-SH) groups and exerts an improving such as ascorbic acid and potassium bromate action. Oxidation is rapid and almost complete (where permitted) or azodicarbonamide, which in doughs mixed for 2.5 min. Short mixing times complete the ‘activation’ commenced by the are thus appropriate. The residue left in the flour cysteine. The dough-softening action of cysteine is biurea. Flour treated with ADA is said to reduces the work input required for the production produce drier, more cohesive dough than that of fully developed dough. treated with chlorine dioxide, to show superiority in mixing properties, and to tolerate higher water Blending for improver treatment absorption. An average treatment rate is 5 mg/kg (on flour weight) in bulk fermentation and low- The principles applied to bleaching flours of speed mixing methods of baking, and 20-25 different grades also apply to improver treatment mg/kg (on flour weight) in the high-speed mixing (cf. Table 7.1). Chorleywood Bread Process (CBP). The agent Emulsifiers and stabilizers does not bleach, but the bread made from treated flour appears whiter because of its finer cell structure. The use of ADA has been permitted, to ‘Emulsifiers’ and ‘stabilizers’ are any substances a maximum level of 45 mg/kg, in the U.K. since capable of aiding formation of (emulsifiers) or 1972. Its usage is also permitted in Canada, New maintaining (stabilizers) the uniform dispersion Zealand and the U.S.A., but not in Australia or of two or more immiscible substances. Flours, in EC countries other than the U.K. (1989). sold as such, are not allowed to contain emulsifiers L-Cysteine is a naturally occurring amino acid, but the following are permitted by the Bread and is used in the Activated Dough Development Flour Regulations (1984) to be included in bread: process (ADD) (cf. Ch. 8), in which it functions E 322 lecithins; E460 a-cellulose (permitted only as a reducing agent. The addition of L-cysteine in bread for which a slimming claim is made); (in the form of L-cysteine hydrochloride or E466 carboxymethyl cellulose, sodium salt (per- L-cysteine hydrochloride monohydrate) to bread mitted only in bread for which a slimming claim doughs, for this purpose, is permitted by the is made); E471 mono- and di-glycerides of fatty Bread and Flour Regulations 1984 in the U.K. acids; E472(b) lactic acid esters of mono- and to a maximum level of 75 mg/kg in bread flours di-glycerides of fatty acids; E472(c) citric acid FLOUR QUALITY 177 esters of mono- and di-glycerides of fatty acids; coarse a flour produces incomplete sheets of E472(e) mono- and di-acetyl tartaric acid esters of unsatisfactory wafers. mono- and di-glycerides of fatty acids; E481 Gluten development in wafer batters must be sodium stearoyl-2-lactylate (cf. Ch. 8); E482 avoided, so flours which have a low tendency to calcium stearoyl-2-lactylate; E483 stearyl tartrate; give an aggregated gluten under low shear rates E481 and E482 are subject to a maximum level in aqueous flour batters are required. Hence low of 5000 mg/kg. protein flours with weak extensible glutens are normally specified (cf. p. 186). Cracker doughs have fully developed gluten networks and protein quality is important in Biscuit (cookie, cracker) flour Biscuit flours for short and semi-sweet biscuits dough processing. Cracker flours with medium are typically produced from grists containing protein contents (9.5-10.5%) made mainly from mainly soft wheats, with some hard wheats hard wheats are commonly used. Matzos are included to increase the rate of production in the water biscuits made from unbleached, untreated mill. However, hard wheat flours produce thinner flour and water only. biscuits than those of soft wheats so it is important Emulsifiers to use a narrow range of levels of hard wheat in the flour. The level specified will depend on the manufacturer’s preference since the biscuit plant Emulsifiers are used in biscuits, either as will have to produce biscuits of particular sizes processing aids or as partial replacements for fat. and weights to suit the packing plant. Very low levels (e.g. 0.1% on fat basis) of sodium There is no developed gluten network in short stearoyl-2-lactylate (E48 1) in sheeted biscuit biscuit doughs, hence neither the level nor quality doughs produce a smooth, non-sticky surface of protein is significant in production. However, which aids dough-piece cutting. Lecithin (E322) consistency of quality is critically important in is commonly used in wafer batters to aid release of modern, high-speed production plants. Flours the baked wafer from the wafer baking machinery. would normally be specified to have, say, a range Emulsifiers which can replace a substantial propor- of 1% protein within the typical range for flours tion of fat in biscuits without serious deterioration (8-1 0%). in product quality are sodium stearoyl-2-lactylate Semi-sweet biscuits have a developed gluten and the diacetyltartaric acid esters of mono- network which is modified during processing, glycerides of fatty acids E472e. Lecithin can be and for these biscuits low protein flours (typically used to replace a low level of fat in biscuits. 8.5-9.5%) with weak, extensible glutens are used. Flours for confectionery products At present, sulphur dioxide (SO*, usually obtained from sodium metabisulphite added at the mixer) Cake flours is used to increase the extensibility and decrease the elasticity of the doughs. This aids control of the dough sheet and hence biscuit thickness. EC Flour in cakes should allow an aerated structure proposals include permission of SO2 in fine to be retained after the cake has been built up. bakery wares, up to 50 mg/kg in the final product. The stability of the final cake depends largely Nevertheless wheat breeders are seeking to develop upon the presence of uniformly swollen starch varieties which perform well without its use. granules; hence, the granules should be undamaged For wafers, low protein flour milled from weak during milling, free from adherent protein, and wheat is suitable. Particle size is an important unattacked by amylolytic enzymes. These charac- characteristic; ideally about 55% should be below teristics are found in flour milled from a soft, 40 pm, 35% between 40 and 90 pm, and not more low-protein wheat of low alpha-amylase activity. than 10% coarser than 90 pm. Too fine a flour Typical parameter values for cake flour milled produces light, tender, fragile wafers, while too in the U.K. would be as follows: Untreated cake 178 TECHNOLOGY OF CEREALS flour: 8.5-9.5% protein and aminimum of particles at a level of about 0.5-1 .O% of batter weight, exceeding 90 pm in size. Fine particle size is more whisking times can be greatly reduced, all-in important than low protein content for cake mixing methods can be used and liquid egg can quality, giving finer, more even crumb than that be replaced with dried egg. given by a coarser flour. Foam-promoting emulsifiers such as GMS, Strong cake flour (for fruit cakes): 12% poly-glycerol esters, propylene-glycol esters (E477) protein, 20-25 FU starch damage, 0.18% chlorine or blends of these, used at about 1% of batter treatment. weight, allow a reduction in the fat content of a cake or even substitution of the fat by a smaller quantity of vegetable oil. Although anti-staling effects of emulsifiers in High-ratio flour In the late 1920s it was discovered, in the cakes are not as clearly defined as in bread, U.S.A., that cake flour which had been bleached sucrose esters (E473), sodium stearoyl lactylate with chlorine gas to improve its colour permitted (E481) and poly-glycerol esters (E475) offer some production of cakes from formulae containing possibilities as a means of minimizing the effects levels of sugar and liquid each of which is in of staling. excess of flour weight. Such flour for use in high sugar/flour ratio and high liquid/flour ratio Flour for cake premixes formulae is known as ‘high-ratio flour’. It should also have fine, uniform granularity and low protein Some cake premixes sold in Britain contain, in content. The chlorination treatment, generally powder form, all the ingredients required for a 0.1-0.15% by weight, besides allowing addition cake, viz. flour, fat, sugar, baking powder, milk of larger proportions of liquid and sugar, reduces powder, eggs, flavouring and colour, and need only elasticity of the gluten and lowers the pH to 4.6- the addition of water before baking. However, 5.1. some cake premixes, particularly those sold in the Heat treatment of the grain or of the semolina U.S.A., omit the eggs and/or the milk, because from which the flour is milled has been found to lighter cakes of larger volume can be made by the be an effective substitute for the chlorine treat- use of fresh eggs instead of dried ingredients. ment of high-ratio cake flour (BP nos 1444173 The type of flour must be suitable for the (FMBRA) and 1499 986 (J. Lyons)) (cf. p.171) particular product, flours of high-ratio type gener- and cake flours may be similarly treated. ally being used. The fat must have the correct Typical characteristics of high-ratio flour milled plasticity and adequate stability to resist oxida- in the U.K. would be 768.4% protein, 2&25 FU tion. The addition of certain antioxidants to fat, starch damage, granularity such that 70% of the to improve stability, is allowed in Britain, the particles were below 32 pm in size and a minimum U.S.A. , and elsewhere. Those allowed in Britain of particles exceeding 90 pm in size. High-ratio under the Antioxidants in Food Regulations 1978 flour is particularly suitable for sponge-type goods. (S.1 1978 No. 105, as amended) for addition to anhydrous oils and fats, and certain dairy products other than butter, for use as ingredients are propyl, octyl or dodecyl gallates up to 100 mg/kg, Emulsifiers in cakes In cake making, emulsifiers such as glycerol or butylated hydroxyanisole (BHA) and/or monostearate (GMS) and mono- and di-glycerides butylated hydroxytoluene (BHT) up to 200 of fatty acids (E471) are used in soft fats at levels mg/kg (calculated on the fat). Those allowed in of up to 10% to produce high-ratio shortenings. the U.S.A. (with permitted levels based on fat or Certain emulsifiers such as GMS, polyglycerol oil content) are: resin guaiac (0.1%), tocopherols esters and lactic acid esters of mono-glycerides (0.03%), lecithin (0.01%)) citric acid (0.01%), (E472b) possess remarkable foam-promoting pyrogallate (0.01%), propylgallate (0.02%) and properties so that when added to sponge batters BHA and/or BHT (0.02%). FLOUR QUALITY 179 wheat has been denatured it is not suitable for breadmaking. The flour may, for many purposes, be regarded as impure starch, and is often used to replace starch in certain types of adhesives, and as a filler for meat products. The bacteriological status of flour for soups is important and requires not > 125 total thermo- philic spores per 10 g, not >50 flat sour spores per 10 g, not >5 sulphide spoilage organisms per 10 g, thermophilic anaerobic spores in not >3 tubes out of 6. Quellmehl Quellmehl or heat-treated starch, is defined as maize flour or wheat flour of which the starch has undergone hydrothermic (vzz. steam) treat- ment resulting in pregelatinization of the starch thereby increasing its swelling capacity by at least 50%. Flour for sausage rusk A low protein flour milled from weak wheat, such as U.K.-grown Riband, or a low protein air- classified fraction is required. Desirable charac- teristics are low maltose figure (not > 1.4 by Blish and Sandstedt method), low alpha-amylase activity (high Falling Number) and high absorbency. Batter flour A low protein flour milled from a grist com- prising 90% weak British wheat plus 10% strong wheat is suitable. Alpha-amylase activity should be low. Too high a viscosity in the batter caused by excessive starch damage is to be avoided, and therefore the proportion of hard wheat in the grist should be restricted. Household flour Household flour is used for making puddings, cakes, pastry, etc. In the U.K. it is milled from a grist consisting predominantly of weak wheats of low protein, such as British or Western European, with admixture of up to 20% of strong wheat to promote flowability and good mixing. Exclusion In preparing the premixes, the dry ingredients are measured out by automatic measures and conveyed, often pneumatically, to a mixing bin, mixed, and then entoleted (cf. p. 111) to ensure freedom from insect infestation. The fat is then added, and the mixture packaged. If fruit is included in the formula, it is generally contained in a separate cellophane-wrapped package enclosed in the carton. Flour for fermented goods For buns, etc. a breadmaking flour is required. Fermentation time is short; the fat and the sugar in the formula bring about shortening of the gluten. Flour for pastry A weak, medium strength flour is needed for the production of sweet and savoury short pastes. Flour strength for puff pastry will vary according to the processing methods, with rapid processing methods requiring weaker flours than those used in traditional methods of production. In general, flours for puff pastry should have low resistance to deformation (e.g. low Brabender resistance values) but reasonable extensibility. Flour from steamed wheat Flour milled from steamed wheat ('stabilized' flour, in which enzymes have been inactivated) is produced for use in manufacture of soups (Ch. 7), gravies, crumpets, liquorice and as a thickening agent. For these purposes, the flour should form a thick paste when it is heated with water, and the paste should retain its consistency for some time when heated at 9Oo-95"C. The alpha-amylase activity of normal (non-steam-treated) flour is usually high enough to degrade swollen starch granules during the cooking process, resulting in loss of water-binding capacity and formation of thin pastes of low apparent viscosity. The greater water-absorbing capacity of the flour from steamed wheat could also make it a suitable ingredient for canned pet-foods. As the gluten in the flour from steam-treated 180 TECHNOLOGY OF CEREALS of sprouted wheat from the grist is important (cf. acid pyrophosphate (SAPP) diluted with starch Ch. 4), as high alpha-amylase activity leads to the and used in the ratio of 2: 1 with sodium hydrogen production of dextrins and gummy substances carbonate at a rate of 4.7% on flour weight. during cooking, and to sticky and unattractive lnstantized or agglomerated flour baked goods. This a form of free-running flour, readily Self-raising flour dispersible in water, made by ‘clustering’ flour This is a household flour to which raising particles in an ‘Instantizer’. Uses include the agents have been added. Choice of sound wheat making of sauces and gravies and for thickening is important because evolution of gas during and general culinary purposes. In the instantizing baking is rapid and the dough must be sufficiently process, the flour as normally milled is damped distensible, and yet strong enough to retain the with steam, tumbled in a warm air stream to cause gas. The moisture content of the flour should not the particles to agglomerate, then dried, sieved, exceed 13.5% in order to avoid premature reaction cooled and packed. The U.S. standard for agglom- of the aerating chemicals and consequent loss of erated flour requires all the flour to pass through aerating power. a sieve of 840 pm aperture width and not more Distension of the dough is caused by carbon than 20% to pass through a sieve of 70 pm dioxide which is evolved by the reaction between aperture width. Free-flowing flour is also produced the raising agents (U.S.: leavening agents), one by air classification (cf. Ch. 6). alkaline and one acidic, in the presence of water. The usual agents used for domestic self-raising Flour for export flour in the U.K. are 500, sodium hydrogen carbonate (‘bicarbonate’) (NaHC03) and acid Besides the specific requirements according to calcium phosphate, (ACP, E341 calcium tetra- the purpose for which the flour is to be used, hydrogen diorthophosphate) (CaH,(PO&), and flour for export must have low moisture content their use was described by J. C. Walker in BP to prevent development of mould, taint or infesta- No 2973 in 1865. The usual rate of usage is 1.16% tion during its transportation. As a safeguard, the bicarbonate plus 1.61% of 80% grade ACP flour should be entoleted. In addition, export on flour weight. A slight excess of the acidic flour must conform to any special requirements component is desirable, as excess of bicarbonate of the importing country, e.g. regarding the gives rise to an unpleasant odour and a brownish presence or absence of nutrients and improvers, yellow discolouration. The Bread and Flour for which the regulations of most other countries Regulations 1984 permit the following raising differ from those of the U.K. (cf. Ch. 14). agents in the U.K.: 500, sodium hydrogen In January 1988 the (U.S.) Food and Drug carbonate, E341 calcium tetrahydrogen diortho- Administration (FDA) announced guidelines for phosphate (monocalcium phosphate (ACP)), E450 contamination levels at which flour is seizable. disodium dihydrogen diphosphate (sodium acid These levels are 75 insect fragments or more per pyrophosphate (SAPP)), 541 acidic sodium 50 g flour and an average of one rodent hair or aluminium phosphate (SAP), 570 D-glucono-1,5- more per 50 g flour. lactone and E336 mono potassium+( +)-tartrate (cream of tartar). Flours from cereals other than wheat ACP used at a rate of 1.61% on flour weight adds about 250 mg Ca per 100 g flour; hence, Besides wheat, all other cereals yield flour when self-raising flour does not require chalk to be subjected to milling processes as outlined in Ch. added to it (cf. Ch. 14). Phosphate-starch mixtures 6. The uses for these flours, both commercially are known as cream powders, a commonly used and domestically, are many and varied, as the commercial example of which consists of sodium following summary indicates. FLOUR QUALITY 181 The former finds uses in the food industry, while the latter is reported to make a unique beer. The major food uses for malt products and cereal syrups are in bread, biscuits, crackers, crisp- bread, breakfast cereals, infant and invalid foods, malted food drinks, pickles and sauces, sugar confectionery and vinegar. Oat flour Rye flour Rye flour of various extraction rates is used extensively in Eastern Europe for making a range of breads - both soft breads and crispbreads - using conventional straight dough or sour dough processes. Rye flour is also used as a filler for sauces, soups and custard powder, and in pancake flour in the U.S.A., and for making gingerbread in France. A mixture of 10% of rye flour with 90% crackers in the U.S.A. The rye flour is said to expensive than wheat flour. Rye flour can be fractionated by air-classification; a flour of 8.5% protein content yielded high and low protein fractions of 14.4% and 7.3% protein contents match and plastics industries. This is made by grinding oatmeal on stones flour is also obtained as a by-product of groat and for ready-to-eat breakfast cereals, e.g. shredded products made by a continuous extrusion cooking process (Ch. 11) and an extruded gun-puffed product (Ch. 11). concentrate by the air-classification (Ch. 6) of oat flour has been described (Cluskey et al., 1973). (N x 6.25, d.b.) was obtained which comprised 2-5% of the flour by weight. The compound granules of oat starch (Ch. 2) tend to disinte- grate upon fine grinding, releasing the individual granules, which measure 2-10 pm. Separation of an almost pure protein fraction would therefore require the use of an extremely fine Cut size __ less than 2 pm. Of wheat flour is used for making biscuits and and sifting OUt the fine material (cf. Ch. 6). Oat improve the quality Of the products and is less cutting. Uses for oat flour include infant foods respective1y* Rye flour is a1so used in the glue, A process for the separation of a protein Rye flour can also be used for making gun- puffed and shredded ready-to-eat breakfast cereals' An ultra-fme fraction with 85-88% protein content Triticale flour The use of triticale flour in breadmaking is mentioned in Ch. 8, and its use in making chapattis is referred to in Ch. 13. Other bakery products made with triticale flour include pancakes and waffles. Barle y flour Rice flour Barley flour is used in the manufacture of flat bread, for infant foods and for food specialities. It is also a component of composite flours used for making yeast-raised bread (cf. Ch. 8). Pregelatinized barley flour, which has high absorbent properties, provides a good binder and thickener. Barley breading is made by combining pregelatinized barley flour with barley crunch. Malted barley flour is made from barley malt (cf. Ch. 9). Malt flour is used as a high diastatic supplement for bread flours which are low in natural diastatic activity, as a flavour supplement in malt loaves, and for various other food products. Malted barley flour can be air-classified (cf. Ch. 6) to yield protein-rich and protein-poor fractions. This is used in refrigerated biscuit manufacture to prevent sticking; in baby foods, as a thickener; in waffle and pancake mixes, as a water absorbent. The use of rice flour, in blends with wheat flour, to make bread of acceptable quality, is mentioned in Ch. 8, and also its use, as a component of composite flours, for breadmaking. Rice flour can also be used for making pasta products. Maize f,our This is used to make bread, muffins, dough- nuts, pancake mixes, infant foods, biscuits, wafers, breakfast cereals, breadings, and as a filler, binder and carrier in meat products. 182 TECHNOLOGY OF CEREALS Dry milled maize flour is not to be confused through collaborative testing, by various standard- with ‘corn flour’, the term used in the U.K. izing organizations. Most countries have national for maize starch obtained as a product of wet- Standards Organizations (e.g. British Standards milling. Institute, BSI), and international standards are The inclusion of maize flour in composite flour also produced by e.g. the International Association used for breadmaking, and its use, alone, to make of Cereal Science and Technology (ICC), Inter- bread of a sort in Latin America, are mentioned national Standards Organization (ISO) and in Ch. 8. The use of maize flour, in blends with American Association of Cereal Chemists (AACC). wheat semolina, to make pasta products is men- Tests may be applicable to whole grains or tioned in Ch. 10 and for making extrusion-cooked derived products, in the case of whole grains it ready-to-eat breakfast cereals in Ch. 11. may be necessary to grind them to achieve an Industrial uses for maize flour are noted in appropriate particle size distribution. Ch. 15. For valid comparisons to be made it is necessary to observe proper sampling procedures (ICC 130, AACC 64) and to normalize results of most tests to a constant moisture basis. Either a dry matter basis or a 14% moisture basis is usually adopted. As test procedures become more stringent, protocols increasingly demand that test samples contain a consistent dry weight of sample, requiring an adjustment of the actual mass taken to compen- sate for moisture variation, rather than subsequent correction. Moisture content must thus be deter- mined by an acceptable method, such as deter- mination of weight-loss when the ground product is heated at 100°C for 5 h in vacuo or at 130°C for 1 h (flour) or 1.5 h (ground wheat) at atmospheric pressure. (ICC lOl/l). These methods are suitable for moisture contents up to 17%. Oven methods are primary methods as they deter- mine directly the required parameter; secondary propem which varies as a function of the requhed parameter, and thus require calibration against a standard. Secondary methods are frequently more rapid but less accurate than oven methods; hey include electfical conductivi~ and N~~~ infra- Sorghum and millet flours Sorghum flour is used as a component of composite flour for mhg bread in those corntries in which sorghum is an indigenous crop (cf. Ch. 8). The use of flour or wholemeal from sorghum and SOme of the millets to make porridge, Toti, chapatti, tortilla and other products is described in Ch. 13. Sorghum flour finds industrial uses, e.g. as core-binder, resins, adhesives, and in oil-well drilling (cf. Ch. 15). Composite flours lished by the Food and Agriculture Organization in 1964 to find new ways Of using flours Other than wheat - particularly maize, mi11et and sorghum - in bakery and pasta products, with the objective of stimulating local agricultural The Composite F1our Programme was estab- methods may also be used, they measure a production^ and saving foreign exchange, in those countries heavily dependent on wheat imports red Reflectance Spectroscopy (NIRS) methods (IS0 202, covers moisture and protein determina- (Kent, 1985). tions). NIRS determinations are based on absorp- tion of NIR energy at specific wavelengths by OH bonds in water molecules. The same is true of protein determinations where the peptide bonds between amino acids define the critical wave- lengths. Considerable mathematical processing of signals and measurements at reference wave- lengths are necessary to ensure accurate indications of the required parameters. Quality control and flour testing Testing protocols, and acceptable degrees of reproducibility (agreement between laboratories) and repeatability (agreement between replicate determinations by the same operator using the same equipment), have been established, usually FLOUR QUALITY 183 Parameters dependent on the nature of the grains milled Sedimentation tests These provide a useful indication of the suit- ability of a flour (it is more usually performed on Protein content a ground wheat) for breadmaking. The Zeleny Protein content of whole grains, meals and test (Pinkney et al., 1957) (AACC 56-60, ICC flours may be calculated from nitrogen contents 116) has been adopted in a number of countries determined by the Kjeldahl method (AACC 46) for protein evaluation. It depends on the superior in which organic matter is digested with hot swelling and flocculating properties, in a dilute concentrated sulphuric acid in the presence of a lactic acid solution, of the insoluble proteins of catalyst. Ammonia, liberated by addition of an wheats with good breadmaking characteristics excess of alkali to the reaction product, is separ- (Frazier, 1971). In the U.K. a better guide to ated by distillation and estimated by titration. A breadmaking properties has consistently been convenient apparatus is the Tecator Kjeltec 1030 obtained using the SDS sedimentation test (Axford Auto System (IS0 1871). In white wheat flour, et al., 1979) rather than the Zeleny test. The SDS protein content is estimated by multiplying N2 test has been standardized as BS 4317, part 19, content by 5.7, and in many references this factor and it has been adopted for evaluation of T. durum is used for other wheat products and other cereals. quality as ICC 5670 and AACC 15 1. It consists However FAONlrHO (1973) recommend factors of an initial suspension and shaking of ground appropriate to individual foodstuffs. Those relating material in water, to which sodium dodecyl to cereals are given in Table 7.7. sulphate is later added. Following a series of carefully timed inversions of the cylinder con- taining the suspension, it is allowed to stand for 20 min after which the height of sediment is read. The test is performed under controlled temperature conditions. TABLE 7.7 Factors Used forConvertingKjeldah1 Nitrogen toprotein Values Wheat fraction Factor Cereal Factor Wholemeal flour 5.83 Maize 6.25 Flours, except wholemeal 5.70 Rice 5.95 Pasta 5.70 Barley, oats, rye 5.83 Enzyme tests Bran 6.31 One of the most important enzymes influencing flour quality is alpha-amylase. Its activity may be For routine estimations of protein (and moisture) determined directly, using the method of Farrand content NIRS methods are now very reliable for (1964) or McCleary and Sheehan (1987), or whole grains as well as their derivatives. Deter- indirectly, as a result of its solubilizing effect on minations are carried out at intake and on-line starch, leading to a reduction in paste viscosity. during processing, in many cereals plants through- The most widely adopted method uses the Falling out the world. Number apparatus to detect starch liquefaction For determining the amount of wheat protein in a heated aqueous suspension of flour or (more contributing to gluten, the Glutomatic instru- usually) ground grain (ICC Standard Method ment (Falling Number Co) and method may be 107, AACC 56-81B). As enzyme activity can used. A dough is prepared from a sample of flour vary dramatically among individual grains it is or ground wheat, and a solution of sodium essential to grind a large sample of grain (at least chloride. Wet gluten is isolated by washing this 300 g) in preparing a representative meal, and to dough with a solution of buffered sodium chloride mix it thoroughly before taking the test sample and, after removal of excess water, weighed, or (7 g at 15% m/c) from it. Wholemeals also require dried and weighed according to whether wet or regrinding and thorough mixing, and flours have dry gluten content is required (ICC 137, AACC to be free of lumps. Following the preparation of 56-81B). a suspension in a special tube, this is introduced 184 TECHNOLOGY OF CEREALS into the apparatus and the test proceeds auto- matically. The suspension is heated and stirred at a programmed rate for 60 sec, after which a plunger is allowed to fall through it. The Falling foam-type cake tests also appear under Number is the number of seconds from the start of heating to the coming to rest of the plunger. A similar principle underlies stirring tests with the Rapid Visco-Analyser . Used on grain or grain products to measure alpha-amylase, both insments probably also respond to hydrolysis of other viscous components such as proteins and ceu-wall components, but the effects of these are usually comparatively small. Heat damage test for gluten The effect of overheating on gluten is measured directly by a method introduced by Hay and Every (1990). Described as the glutenin turbidity test, the procedure measures the loss in solubility of the fraction of glutenins normally soluble in acetic acid. Dilute acetic acid extracts are precipitated by addition of alkaline ethanol and the precipitate is quantified by spectrophotometric measurement of turbidity allowing the degree of damage to be assessed by comparison with standards. Good correlations have been found between loss of turbidity and reductions in baking quality. Pigmen tation The yellow colour of durum semolinas is highly valued. Under ICC 152 the carotenoid pigments are extracted at room temperature with Water- saturated butanol for Photometric evaluation of Optical density Of the Clear filtrate against a p-carotene standard. End-use tests version of the same. Several bread baking tc appear under AACC 10 and ICC 131, rye flc is tested by AACC 10-70. Biscuit (cookie) E 10-heading. Pasta semolinas are also subjectec approved small scale tests (AACC 66-41 and -4 Machinability test In adopting a test for bread wheats eligible Intervention Price SUPPOrt, the EC has not St dardized a breadmaking test but instead ' defined flour Of breadmaking quality as flc which produces dough which does not 'stick the blades or the bowl of the mixer in which dough is mixed, nor to the moulding apparat Extraneous matter test ('filth test') The rodent hair and insect fragment COUn, flour is determined by digesting the flour ~ acid and adding the cooled digest to petrol i separating funnel. The hair and insect fragme are trapped at the petroVwater interface, and, be collected and identified microscopically. Tests for characteristics dePendent mainlY on Processing conditions Ash test BS 4317 Part 10 The ash test (incineration of the material i furnace at a specified temperature and un prescribed conditions, and the weighing of resultant ash) is widely used as a measure &g refinement because pure starchy endospc yields relatively little ash, whereas bran, aleurc and germ yield much more. The ash test can carried out very precisely, but, as the endospe1 of different wheats vary in mineral content, a gi. ash value can correspond to different levels bran content. The test is not suitable for indicat the content ofnon-stuchy-endosprm compone in flours to which chalk has been added. In spite of much research no single test has Yet been devized which Can reliably predict the breadmaking properties of an unknown wheat or flour. Hence for this application, and for many other applications of cereals, the most reliable means of evaluating a sample is to subject it to the intended end-use itself, or to a scaled down Grade Colour The Grade Colour test, performed, for exam] with the Kent-Jones and Martin Colour Grac FLOUR QUALITY 185 can be used to estimate the degree of contamina- Donelson and Yamazaki (1962) and Barnes (1978) tion of white flour with bran particles. In the test, rely on assaying reducing sugars (mainly maltose) the intensity of light in the 530 nm region, produced by the action of alpha-amylase derived reflected from a standardized flourlwater paste, from malt flour. Another method (Gibson et ai., in a glass cell, is compared with that reflected 1992) employs amyloglucosidase to further hydro- from a paste of a reference flour. The grade colour lyze oligosaccharides to glucose, which is then was said to be unaffected by variation in content determined by the effect of a derivative on a of flour pigment (xanthophyll) (cf. p. 171). It has chromogen. now been demonstrated however, that this is not Damaged starch granules may be recognized so (Barnes, 1978), thus diminishing the value of microscopically by a red coloration with Congo the test as a means of quantifying bran content. Red (colour index: 22120) stain (cf. Ch. 6), and have been described, from their microscopical Tristim ulus methods appearance, as ‘ghosts’ by Jones (1940). Un- damaged granules do not stain with Congo Red. Use of an instrument designed to simulate the A method of damaged starch determination, in visual response of the human eye has found favour which damaged and undamaged granules are in some applications, as an alternative to the measured separately taking advantage of their Grade Colour system. The instrument depends different staining reactions with a fluorescent dye, upon complex mathematical transforms to produce has been developed, using image analysis for values in three arbitrary spectral ranges, X, Y and making the measurements. Z, which cannot be produced by any real lights (Hunter and Harold, 1987). Users can derive a Whiteness index to suit their needs, by selecting Particle size analysis from these values. Like the Grade Colour system Test sieving by hand or sieve shakers tends to it responds to factors other than bran content - be unreproducible on flour, but the Alpine air- probably particle-size - and it thus has a limited jet sieve, in which negative pressure below the usefulness (Evers, 1993). sieve assists particles through the mesh, and clears the mesh with reversed air-jets, gives more reproducible analyses. Sedimentation methods Damaged starch The amount of starch that is mechanically depend upon the faster settling rates of larger damaged influences a flour’s ability to absorb particles, in a non-aqueous solvent; the Andreassen water. The content of damaged starch in flour is pipette is an example of a simple device using estimated by methods which measure either the this principle (ICC 127), another is the Simon digestibility or the extractability of the starch. Sedimentation Funnel. Sedimentation methods Digestibility-based methods measure the amount are not much used today in flour quality control, of hydrolysis effected by added amylase enzymes; having been superseded by more reproducible extractability-based methods measure the amount methods. The Coulter counter is a device which of amylose present in an aqueous extract by its rapidly measures the volume of thousands of reaction with iodine in potassium iodide. The individual particles as they pass through an iodine/amylose complex may be assayed colori- orifice. Each particle is measured by the change metrically (e.g. McDermott, 1980), ampero- in electrical resistance that it causes by displacing metrically or potentiometrically (e.g. Chopin SD 4 its own volume of the electrolytic solution (non- method). Only the damaged granules are suscept- aqueous in the case of flour) in which the particles ible to amylase at temperatures below gelatiniza- are suspended. Reproducibility is very good with tion temperature and appreciable leaching of this method (Evers, 1982) which is suitable for amylose occurs only from damaged granules flours and starches but not wholemeals. Laser under the test conditions. diffraction-based instruments provide a means of Methods such as those of Farrand (1964), making rapid comparisons among flours. There 186 TECHNOLOGY OF CEREALS are many instruments of this type available, some capable of operating on dry samples. The distributions that they indicate may not agree well among different instruments or with those of the other methods described. Physical tests on doughs and slurries The physical characteristics of doughs and slurries are important in relation to the uses of flours. Pseudo-rheological characteristics are investigated mainly with the following: The Brabender Farinograph (D' Appolonia and Kunerth, 1984) measures and records the resist- ance of a dough to mixing as it is formed from flour and water, developed and broken down. This resistance is called consistency. The maximum consistency of the dough is adjusted to a fixed value by altering the quantity of water added. This quantity, the water absorption (cf Ch. 8), may be used to determine a complete mixing curve, the various features of which are a guide to the strength of the flour (AACC 54-21, ICC 115). Preston, 1991) (ICC 114, AACC 54-10) records the resistance of dough to stretching and the distance the dough stretches before breaking. A flour-salt-water dough is prepared under standard conditions in the Brabender Farinograph and moulded on the Extensograph into a standard shape. After a fixed period the dough is stretched and a curve drawn, recording the extensibility of the dough and its resistance to stretching (see Fig. 7.1). The dough is removed and subjected to a further two stretches. The Extensograph has replaced the Extensometer in the Brabender instrument range but the older instrument is still widely used for testing biscuit flours. The Chopin Alveograph (AACC 54-30) uses air pressure to inflate a bubble of dough until it bursts; the instrument continuously records the air pressure and the time that elapses before the dough breaks. The Brabender Amylograph (ICC 126 for wheat and rye flours) continuously measures the resist- ance to stirring of a 10% suspension of flour in water while the temperature of the suspension is raised at a constant rate of l.S"C/min from 20"-95"C and then maintained at 95°C (Shuey and Tipples, 1980). It is of use in testing flour for soups, etc., for which purpose the viscosity of the product after gelatinization is an important The Brabender Extensograph (Rasper and characteristic (cf. Ch. 6), and for adjusting the malt addition to flours for breadmaking (cf. p. 62). The Rapid Visco Analyser (RVA), produced by Newport Scientific, in Australia, may be regarded as a derivative of the Amylograph. weak medium 500 - e v) C 3 .- L 0 E \ \ \ \ 1- $ C d strong % 500 w / 4 $ 9 \ cm 5 10 15 20 5 10 15 20 FIG 7.1 Extensometer curves of unyeasted doughs made from flours of different strengths as indicated. FLOUR QUALITY 187 Measurements of viscosity are made using small 32 kg when packed; the multiwall kraft paper samples, containing 34 g of starch, in periods bags are stacked, often several tiers high, on pal- which may be as short as 2 min. Use of disposable leting. The harshness of treatment to be expected containers and mixer paddles eliminates the need during filling and handling influences the number for careful washing of the parts between tests. As of plys in the walls of the chosen bags. Using with the Amylograph, the characteristics of starch single-spout packers approximately 300-350 bagsh pastes and the effects of enzymes on them can be can be filled. Using multi-spout packers, with up recorded on charts. They can also be transferred to 8 spouts, 600-800 bags/h are possible. in digital form, direct to a data-handling computer. The hazards to flour in storage include those The capacity for measuring the liquefying to wheat in storage, vzz. mould and bacterial effects of enzymes on viscous pastes enables the attack, and insect infestation (cf. Ch. 6) and RVA to be used for detecting the products of also oxidative rancidity (cf. Ch. 3) and eventual sprouted grains in cereal meals. deterioration of baking quality. True rheological instruments. In recent years Freedom from insect infestation during storage frustration with instrument-dependent units can be ensured only if the flour is free from insect obtained with some of the above methods, together life when put into store, and if the store itself is with the poor reproducibility from one instru- free from infestation. Good housekeeping in the ment to another of the same type, has led cereal mill and the milling of clean grain should ensure chemists to turn to true rheological measure- that the milled flour contains no live insects, ments. Suitable instruments for use with doughs, larvae or eggs, but as a precautionary measure slurries and gels, derived from flours, include flour is often passed through an entoleter before the Boklin VOR (viscometric, oscillation and being bagged off, or going to bulk bins. The relaxation), the Carri Med CSL Rheometer and entoleter (BP No 965267) is a machine consisting the Rheometrics RDA2. In addition to providing of a rotor rapidly rotating within a fixed housing. excellent reproducibility, these instruments, which The flour is fed in centrally and is flung with are also used on many non-food, and many non- considerable impact against the casing. At normal cereal food materials, allow comparisons to be speeds of operation (2900 rev/min for flour) the made across a wide range of substances. Although machine effectively destroys all forms of insect they are expensive, and may never feature life and of mites, including eggs (cf. Ch. 5). The prominently in routine testing, they will undoubt- insect fragments, however, are not removed from edly enable the development of tests that can be the flour by the entoleter. performed on simpler, dedicated instruments The optimum moisture content for the storage (Faridi and Faubion, 1990). of flour must be interpreted in relation to the length of storage envisaged, and to the prevailing ambient temperature and r.h., remembering that flour will gain or lose moisture to the surrounding Storage of flour It has been recommended that, for long periods atmosphere unless packed in hermetically sealed of conservation, flour should be stored in a closed containers. For use within a few weeks, flour can atmosphere (Bellenger and Godon, 1972). In be packed at 14% m.c., but at moisture contents these conditions, flour acidity increases owing higher than 13% mustiness, due to mould growth, to accumulation of linoleic and linolenic acids, may develop, even if the flour does not become which are slowly oxidized; reduction of disulphide visibly mouldy. At moisture contents lower than groups (-S-S-) is slow, and there is little increase 12%, the risk of fat oxidation and development in sulphydryl groups (-SH); solubility of gluten of rancidity increases. The reactions involved in protein decreases; as a result, changes in baking oxidative rancidity are catalyzed by heavy metal strength are only minor. ions, such as Cu*+. Flour is stored commercially in bags or in bulk The expected shelf life of plain (Le. non-self- bins. Bags of flour in the U.K. contain 50 or raising) white flour packed in paper bags and 188 TECHNOLOGY OF CEREALS stored in cool, dry conditions and protected from infestation is 2-3 years. The rate of increase in acidity increases with temperature rise and with fall in flour grade (i.e. as the ash residue increases). Hence, the shelf-life of brown and wholemeal flours is shorter than that of white flour. Stored at 17°C (62"F), the shelf-life of brown flour of 85% extraction rate and of wholemeal (100% extraction rate) is closely related to the moisture content and temperature. Brown flour, for instance, should keep 9 months at 14% m.c., 4-6 months at 14.5% m.c., 2-3 months at 15.5% m.c. For wholemeal stored under the most favour- able conditions, a shelf life of 3 months may be expected, or of 12 months if the product has been entoleted. Flour blending Blending of finished flours is widely practised on the continent of Europe and it is becoming increasingly popular in the U.K. It can ensure greater uniformity in a product and it can provide flexibility in response to requirements for flours of unusual specification, through the blending of separately stored flours of various types. Blending can be performed as a batch process or on a volumetric basis. The simpler volumetric method depends upon flours being discharged from two or more bins into a common conveyor, their discharge rates being controlled to provide the respective proportions required. The more accurate batch method involves the use of weighers to deposit required weights of products from each of the selected bins into a batch mixer. An additional advantage of the batch system is that improvers can be added at the same time as the flours are mixed. The mixers used may be of the ribbon type where the blend is continually tumbled, or the air mixer type in which the blend is agitated by air injected into a holding bin. Bulk storage and delivery of flour The storage of flour in bulk bins, and delivery in bulk containers, has advantages over storage and delivery in bags. Although constructional costs of bulk storage facilities are high, the running costs are low because manhandling is much reduced, and warehouse space is better utilized. The capacity of bins for storing flour in bulk is 70-100 t. Packing pressure inside the bin increases with bin area, not with bin height; a bin area of 5.6 m2 is satisfactory. Normally bins are constructed of concrete or metal. Wooden bins are liable to become infested. The choice of construction material is a personal one but steel is currently most popular as metal bins are cheaper (unless capacity is over 20,000 tonnes), they do not crack, they are easily installed and relocated, and they are immediately usable on completion of construction (Anon., 1989). The inner surfaces must be smooth to allow stock to slide down the walls. Steel bin walls are usually coated with shellac varnish and lower parts may be painted with a low-friction polyurethane paint. Concrete surfaces are ground and coated with several coats of sodium silicate wash to provide a seal. The shape of bins is again a matter of choice. Circular bins are cheaper as lighter gauge steel may be used, however, there is more space wasted between cylindrical bins than between rectangular bins. A problem that can arise, when flour is discharged from the base of the bin, is bridging of stock: this can be avoided by good hopper design and efficient dischargers. Bins may be filled and emptied pneumatically; fluidizing dischargers use 0.8-1.1 m3/min of low-pressure air (20-70 kN/m2) to fluidize the flour, causing it to behave as a liquid and to flow down a reduced gradient to the outlet. Mechanical (worm or screw type), and vibratory dischargers may also be used to assist discharge of flour from bins. When flour and air are present in appropriate proportions there is a risk of dust explosions if a source of ignition is also present. In all flour conveying and handling situations, it is essential to avoid sources of ignition arising. Additional precautions include the incorporation of explosion relief panels into bin tops. Similar panels are recommended in the areas of buildings surrounding the bins. Flour was first delivered in bulk in the 1950s and by 1987, 65% of flour delivered in the U.K. was in bulk (Anon., 1989). Bulk wagons for transport can be filled at the FLOUR QUALITY 189 FARRAND, E. A. (1964) Modern bread processes in the United Kingdom with special reference to a-amylase and starch damage. Cereal Chem. 41: 98-1 11. FRAZIER, P. (1971) A Physico-chemical Investigation into the Mechanism of the Zeleny Test. PhD thesis. GIBSON, T. s.9 ALQUALLA, H, and MCCLEARY, B. v. (1992) An improved enzymic method for the measurement of starch damage in wheat flour. 3. Cereal Sci. 15: 15-27. GUY, R. (1993) Ingredients. In: The Technology of Extrusion Cooking. N. FRAME. (Ed.) Blackie, Glasgow. HAY, R. L. and EVERY, D. (1990) A simple glutenin turbidity test for the determination of heat damage in gluten. J. Sci. Food Agric. 53: 261-270. HOLLAND, B, WELCH, A. A., UNWN, I. D., Buss, D. H., PAUL, A. A. and SOUTHGATE, D. A. T. (1991) McCance and Wddmson’s The Composition of Foods, 5th edn, The Roy. SOC of Chem. Cambridge. HUNTER, R. S. and HAROLD, R. W. (1987) The Measurement ofAppearance. 2nd Edn. John Wiley & Sons, NY. U.S.A. JONES, C. R. (1940) The production of mechanidy damaged starch in milling as a governing factor in the diastatic activity of flour. Cereal Chem. 15: 133-169. KENT, N. L. (Technical Ed.) (1985) Technical compendium mill by gravity feed or by blowline, or, most efficiently, by fluidzed delivery from an outload bin direct1y above the vehic1e* By this method flow rates of 250-300 t/h can be achieved. Dis- charge of the vehicle is assisted by air pressure; some larger tankers have a fluidizing Pad in the base of each hopper. Compressors mounted either On the vehic1e Or at the customer’s premises b1ow the de1ivery direct to the storage bins at the bakery. Mini-bulk containers, holding up to about 2 t, may be Used in Some mil1S for transport and delivery of products - mainly bran and germ, but in some cases flour also. References AMERICAN ASSOCIATION OF CEREAL CHEMISTS INC. (1962) on composite flours. Economic Commission for Africa, Cereal Laboratory Methods, 7th edn, Amer. hoc. of Addis Ababa. Cereal Chemists Inc., St. Paul MN., U.S.A. MCCANCE, R. A. and WIDDOWSON, E. M. (1967) The ANON. (1989) Flour milling correspondence course. Product composition of Foods. Med. R~~ coun., spec. Rpt ser. Handling, StorageandDisnibutia. (Moduk 10). Incorporated 297. znd I~~., H.M.s.o., London. National Association of British and Irish Millers, London. MCCLEARY, B. V. and sHEEHAN, H. (1987) Measurement AXFORD, D. W., MCDERMOTT, E. E., and REDMAN, D. G. of cereal alpha-amylase: a new assay procedure. J. Cereal (1979) A note on the sodium dodecyl sulphate test for sei. 6: 237-251. breadmaking quality: comparison with Pelshefie and MCDERMOTT, E. E. (1980) The rapid, non-enzymic deter- Zeleny tests. Cereal Chem. 56: 582-584. mination of damaged starch in flour. 3. Sci Food Agric. BARNES, W. C. (1978) The rapid enzymic determination of 31: 405-413. starch damaged wheat. Staerke 30: 115-119. MELLANBY, E. (1946) Diet and canine hysteria. Brit. Med. BELLENGER, P. and GODON, B. (1972) Influence de l’aeration J. ii: 885. sur I’evolution de diverse caracteristiques biochimiques et MINISTRY OF AGRICULTURE, FISHERIES AND FOOD (1984) physicochimiques. Ann. Technol. Ap’c. 21: 145. The Bread and Flour Regulations 1984 Statutary Instruments BENTLEY, H. R., MCDERMOTT, E. E., MORAN, T., PACE, 1984, No. 1304, as amended by the Potassium Bromate 1. and WH1TEHEAD, 1. K* (1950) Toxic factor from (Prohibition asa Flourlmprover) Regulations 1990(SI 1990, ‘Agenized’ protein. Nature, Lond. 165: 150. No. 399) H.M.S.O., London. CHAMBERLAIN, N. and COLLINS, T. H. (1977) The PINKNEY, A. J., GREENAWAY, W. T. and ZELENY, L. (1957) ChorleYWood bread Process: The imPortance Of air as a Further developments in the sedimentation test for wheat dough ingredient. FMBRA Bull. 4 (Aug): 122. quality. Cereal Chem. 34: 16. CLUSKEY,J. E., WU, Y. V., WALL, J. s. and INGLEn, G. RANUM, p. (1992) Potassium bromate in bread baking. E. (1973) Oat protein concentrates from a wet-milling Cereals Foods World 37: 253-258. process: preparation. Cereal Chem. 50: 475. RASPER, V. F. and PRESTON K. R. (1991) The Extensograph D’APPoLoNIA, B. L. and KUNERTH, w. H. (1984) The Handbook. Amer. Assoc of Cereal Chemists Inc. St. Paul, Farinograph Handbook, 3rd edn, American Assoc of Cereal MN. U.S.A. Chemists Inc. St Paul, MN. U.S.A. SHUEY, W. C. and TIPPLES, K. H. (1980) The Amylograph DONELSON, J. R. and YAMAZAKI, w. T. (1962) Note On a Handbook. Amer. Assoc. of Cereal Chemists Inc. St Paul, rapid method for the estimation of damaged starch in soft MN. U.S.A. wheat flours. Cereal Chem. 39: 460-462. EVERS, A. D. (1982) Methods for particle-size analysis of EVERS, A. D. (1993) On-line quantification of bran particles in white flour. Food Sci Technol. Today 7, 23-26. FAONCTHO (1973) Energv and Protein Requirements. Report of a joint FAONHO Ad Hoc Expert Committee. FA0 Nutrition Meetings Report Series, No. 52, WHO Technical Report Series, No. 522. FARIDI, H, and FAUBION, J. M. (1990) Dough Rheology and Baked Product Texture, Van Norstrand Rheinhold. NY. flour: a collaborative test. Lab. Practice 31: 215-219. Further Reading ANON. (1980) Glossary of Terms for Cereals and Cereal Products. British Standards Institution, London. ANON. (1989) Glossary ofBaking Tern, American Institute of Baking. Manhattan, KS. U.S.A. ANON. (1990) Flour Treatments & Flour Products. Module 12 in Workbook Series, National Association of British and Irish Millers, London. DENGATE, H. N. (1984) Swelling, pasting and gelling of 190 TECHNOLOGY OF CEREALS wheat starch. Advances in Cereal Science and Technology. MARTIN, D. J. and STEWART, B. G. (1987) Dough stickiness 6: 49-82. in rye-derived wheats. Cereal Foods World. 32: 672-673. FARIDI, H. and RAWER, V. F. (1987) The Alveograph MISKELLY, D. M. and MOSS, H. J. (1985) Flour quality Handbook. Amer. Assoc. of Cereal Chemists Inc. St. Paul requirements for Chinese noodle manufacture. J. Cereal MN. U.S.A. Sci. 3: 379-387. FARRAND, E. A. (1972) Controlled levels of starch damage OSBORNE, B. G., FEARN, T. and HINDLE, P. H. (1993) in a commercial U.K. bread flour and effects on absorp- Practical Near Infrared Spectoscopy 2nd Edition. Longmans, tion, sedimentation value and loaf quality. Cereal Chem. Harlow, Essex. 49: 479. PAYNE, P. I., NIGHTINGALE, M. A. KRAITIGER, A. F. and GRAVELAND, A., BOSVELD, P., LITCHENDONK, W. J. and HOLT, L. M. (1987) The relationship between HMW MOONEN, J. H. E. (1984) Structure of glutenins and their glutenin subunit compostion and the breadmaking quality of breakdown during dough mixing by a complex oxidation- British-grown wheat varieties.J. Sci. Food Agric. 40: 51-65. reduction system. pp. 59-68 In: Gluten Proteins. A. POMERANZ, Y., BOLLING, H. and ZWINGELBERG, H. (1984) GRAVELAND and J. H. E. MOONEN (Eds), Inst. Cereals, Wheat hardness and baking properties of wheat flours. Flours and Bread, TNO Wageningen, The Netherlands. J. Cereal Sci. 2: 137-143. GREER, E. N. and STEWART, B. A. (1959) The water POMERANZ, Y. (1983) Single, universal, bread baking test absorption of wheat flour; relative effects of protein and -why not? pp. 685-690 In: Progress in Cereal Chemistry starch. J. Sci. Food Agric. 10: 248-252. and Technology, J. HOLAS and J. KRATOCHVIL (Eds.) MACRITCHIE, F. (1980) Physicochemical aspects of some Elsevier Science Publishers, N.Y. problems in wheat research. Advances in Cereal Science SCHNEEWEISS, R. (1982) Dictionary of Cereal Processing and Technology, 3: 271-326. and Cereal Chemistry. Elsevier Scientific Publishing Co. Amsterdam.