12 Wet Milling: Starch and gluten Purpose of wet milling gluten comprise the steps of extracting the crude Wet milling of cereal grains differs fundament. starch and crude protein, purifying, concentrating ally from dry milling in being a maceration and drying the two products. In order to obtain process in which physical and chemical changes gluten in a relatively pure form(in addition to occur in the nature of the basic constituents starch)it is necessary to separate the gluten from the bran and germ This may be done by first starch, protein and cell wall material-in order milling the wheat by conventional dry processes to bring about a complete dissociation of the endosperm cell contents with the release of the and using the white four as the starting material starch granules from the protein network in for the wet process which they are enclosed In dry milling, the Until the development of recent method endosperm is merely fragmented into cells or cell processes starting with flour were mostly variants fragments with no deliberate separation of starch on three long-established methods from protein (except in protein displacement Martin process: dough is kneaded under water milling by extension of dry milling; cf. p. 132). Although the grains of all cereals contain Batter process: a flour-water batter is dispersed starch, those most widely processed by wet milling in more water so that the gluten breaks down are wheat and maize. Other cereals which are less into small curds. The gluten Is separated frequently wet milled are rice, sorghum and the starch milk by screening millet, while experimental work has been carried Alkali process: four is suspended in an alkaline out to separate starch and protein from triticale solution(e. g 0.03 N sodium hydroxide)in which the protein disperses. Starch is removed by tabling and rye and centrifuging, and the protein precipitated by acidifying to pH 5.5. The protein product is in heat a denatured condition i.e. non-vital A number of modern processes start with flour: .. Means for separating starch from wheat by wet the Canadian process(1966)resembles the alkali milling processes have been known from classical process, but suspends the four in 0.2 M ammonium times. Marcus Porcius Cato (234-149 B.C. hydroxide; the Far-Mar-Co process(U.S. Pat described a process in which cleaned wheat was No. 3, 979, 375)is similar to the martin process, steeped for 10 days in twice its weight of water, but the dough moves through a tube in which the water poured off, the soaked wheat slurried, it is washed and mixed the Alfa-Laval/Raisio enclosed in a cloth, and the starch milk pressed process( Starke, 1978, 30: 8)resembles the batter out. The residue of gluten, bran and germ would process, but uses centrifuging, decantation and have been discarded or used as animal feed hydrocyclones for separating the starch from the All wet processes for manufacture of starch and gluten; the Koninklijke Scholten-Honig process 259
I2 Wet Milling: Starch and Gluten Purpose of wet milling Wet milling of cereal grains differs fundamentally from dry milling in being a maceration process in which physical and chemical changes occur in the nature of the basic constituents - starch, protein and cell wall material - in order to bring about a complete dissociation of the endosperm cell contents with the release of the starch granules from the protein network in which they are enclosed. In dry milling, the endosperm is merely fragmented into cells or cell fragments with no deliberate separation of starch from protein (except in protein displacement milling by air-classification, which is a special extension of dry milling; cf. p. 132). Although the grains of all cereals contain starch, those most widely processed by wet milling are wheat and maize. Other cereals which are less frequently wet milled are rice, sorghum and millet, while experimental work has been carried out to separate starch and protein from triticale and rye. gluten comprise the steps of extracting the crude starch and crude protein, purifying, concentrating, and drying the two products. In order to obtain gluten in a relatively pure form (in addition to starch) it is necessary to separate the gluten from the bran and germ. This may be done by first milling the wheat by conventional dry processes and using the white flour as the starting material for the wet process. Until the development of recent methods, processes starting with flour were mostly variants on three long-established methods: Martin process: dough is kneaded under water sprays. The gluten agglomerates, and the starch is washed out. Batter process: a flour-water batter is dispersed in more water so that the gluten breaks down into small curds. The gluten is separated from the starch milk by screening. Alkali process: flour is suspended in an alkaline solution (e.g. 0.03 N sodium hydroxide) in which the protein disperses. Starch is removed by tabling and centrifuging, and the protein precipitated by acidifying to pH 5.5. The protein product is in a denatured condition, i.e. non-vital. A number of modern processes start with flour: Wheat Means for separating starch from wheat by wet the Canadian process (1966) resembles the alkali milling processes have been known from classical process, but suspends the flour in 0.2 M ammonium times. Marcus Porcius Cat0 (234-149 B.C.) hydroxide; the Far-Mar-Co process (U.S. Pat. described a process in which cleaned wheat was No. 3,979,375) is similar to the Martin process, steeped for 10 days in twice its weight of water, but the dough moves through a tube in which the water poured off, the soaked wheat slurried, it is washed and mixed; the Alfa-Laval/Raisio enclosed in a cloth, and the starch milk pressed process (Starke, 1978, 30:8) resembles the batter out. The residue of gluten, bran and germ would process, but uses centrifuging, decantation and have been discarded or used as animal feed. hydrocyclones for separating the starch from the All wet processes for manufacture of starch and gluten; the Koninklijke Scholten-Honig process 259
(BP 1, 596, 742)also resembles the batter process is met by imports of gluten, chiefly from the and uses hydrocyclones. A process by Walon European continent. Imports of gluten in 1988/ U.S. Pat. No. 4, 217, 414)uses bacterial alpha- 89 amounted to 37,000 t, giving a total availability amylase to solubilize the starch; the gluten is not of about 57,000 t. World production of vital Some modern processes start with wheat but 1988), of which 130,000 t were produceda, denatured and can be separated as 'vital gluten,. gluten in 1986 is reported as 253, 000 t(Gode iffer from Cato's method in using a steep liquor western Europe and 54, 000 t in the u.s.A., containing 0.03-0.7% of sulphur dioxide to inhibit Canada, Mexico and Argentina development of micro-organisms. After draining off the steep liquor, the wet grain is coarsely milled and slurried with water. The bran and Uses for vital wheat gluten germ are separated by screening, and the heavy Vital gluten is used as a protein supplement tarch granules separated from the light gluten curd by sedimentation and centrifuging at levels of 0.5-3.0% to improve the texture In the Pillsbury process(Br. Pat. No. 1, 357, 669 and raise the protein content of bread, par grain is steeped in an acid medium with applica- ticularly 'slimming' bread, crispbread and tion of vacuum or carbon dioxide to remove the speciality breads such as vienna bread and air pocket at the base of the crease where micro- hamburger rolls organisms might develop. In the Far-Mar-Co to fortify weak flours, and to permit the use process(U.S. Pat. No. 4, 201, 708)wheat is soaked by millers of a wheat grist of lowered strong in water and faked. The flakes are disintegrated weak wheat ratio (particularly in the EC and the resulting bran-germ and endosperm countries) by raising the protein content of particles are hydrated and form a dough-like mass the milled four: which is tumbled and manipulated in water to - in starch-reduced high protein breads(cf.p separate and recover vital gluten, starch and bran 209), in which the gluten acts both as a source germ components of protein and as a texturizing agent; In all processes, the starch and gluten are dried n high-fibre breads (cf. p. 209)now being using, in the case of gluten, methods such as made in the U.s. A, to maintain texture and freeze-drying which do not denature the gluten 'Vital'gluten, or undenatured gluten, is gluten Vital gluten is also used as a binder and to raise separated from wheat by processes which permit the protein level in meat products, e.g. sausages, the retention of the characteristics of natural breakfast foods, pet foods, dietary foods and gluten, viz. the ability to absorb water and form textured vegetable products(t v.p. an extensible, elastic mass. Commercial glutens are produced in the U. K, Europe, Australia and Canada(McDermott, 1985). In the U. K, some Vital gluten in bread 260,000-270,000 tonnes of wheat were used in In the U. K, domestic bread consumption in 1988/89 for the manufacture of starch and vital 1988 averaged 30.28 oz/person/week. With a gluten, chiefly by the dough(Martin) or batter population of about 57 million, the total domestic processes, which start with four. So far as is bread consumption would have been about 2.5 known, processes such as the pillsbury and Far- million tonnes per year, or about 2.75 million Mar-Co processes that start with wheat grain are tonnes total consumption, allowing for about 10% not currently being used in the U. K consumed non-domestically. with about 45,000 With a yield of about 0.075 t of gluten from t of vital gluten used in bread in the U. K.in each tonne of wheat, the quantity of gluten 1988, the average level of use would have bee produced in the U. K. in 1988/89 would have been about 1.6%. The usual rates of addition are 1.5% some 20,000 t. The demand for vital gluten in for white bread and 4.5% for wholemeal bread the U. K. considerably exceeds this figure, and In the u.s. a. about 70% of all vital wheat
260 TECHNOLOGY OF CEREALS (BP 1,596,742) also resembles the batter process and uses hydrocyclones. A process by Walon (U.S. Pat. No. 4,217,414) uses bacterial alphaamylase to solubilize the starch; the gluten is not denatured and can be separated as ‘vital gluten’. Some modern processes start with wheat but differ from Cato’s method in using a steep-liquor containing 0.03-0.7°/~ of sulphur dioxide to inhibit development of micro-organisms . After draining off the steep liquor, the wet grain is coarsely milled and slurried with water. The bran and germ are separated by screening, and the heavy starch granules separated from the light gluten curd by sedimentation and centrifuging. In the Pitlsbury process (Br. Pat. No. 1,357,669) grain is steeped in an acid medium with application of vacuum or carbon dioxide to remove the air pocket at the base of the crease where microorganisms might develop. In the Far-Mar-Co process (U.S. Pat. No. 4,201,708) wheat is soaked in water and flaked. The flakes are disintegrated and the resulting bran-germ and endosperm particles are hydrated and form a dough-like mass which is tumbled and manipulated in water to separate and recover vital gluten, starch and brangerm components. In all processes, the starch and gluten are dried using, in the case of gluten, methods such as freeze-drying which do not denature the gluten. ‘Vital’ gluten, or undenatured gluten, is gluten separated from wheat by processes which permit the retention of the characteristics of natural gluten, viz. the ability to absorb water and form an extensible, elastic mass. Commercial glutens are produced in the U.K., Europe, Australia and Canada (McDermott, 1985). In the U.K., some 260,000-270,000 tonnes of wheat were used in 1988/89 for the manufacture of starch and vital gluten, chiefly by the dough (Martin) or batter processes, which start with flour. So far as is known, processes such as the Pillsbury and FarMar-Co processes that start with wheat grain are not currently being used in the U.K. With a yield of about 0.075 t of gluten from each tonne of wheat, the quantity of gluten producedin the U.K. in 1988/89 would have been some 20,000 t. The demand for vital gluten in the U.K. considerably exceeds this figure, and is met by imports of gluten, chiefly from the European continent. Imports of gluten in 1988/ 89 amounted to 37,000 t, givinga totalavailability of about 57,000 t. World production of vital gluten in 1986 is reported as 253,000 t (Godon, 1988), of which 130,000 t were produced in western Europe and 54,000 t in the U.S.A., Canada, Mexico and Argentina. uses for vital wheat gluten Vital gluten is used as a protein supplement: - at levels of 0.5-3.0% to improve the texture and raise the protein content of bread, particularly ‘slimming’ bread, crispbread and speciality breads such as Vienna bread and hamburger rolls; - to fortify weak flours, and to permit the use by millers of a wheat grist of lowered strong/ weak wheat ratio (particularly in the EC countries) by raising the protein content of the milled flour; - in starch-reduced high protein breads (cf. p. 209), in which the gluten acts both as a source of protein and as a texturizing agent; - in high-fibre breads (cf. p. 209) now being made in the U.S.A., to maintain texture and volume. Vital gluten is also used as a binder and to raise the protein level in meat products, e.g. sausages, breakfast foods, pet foods, dietary foods and textured vegetable products (t.v.p.). ,,ital gluten ;,, bread In the U.K., domestic bread consumption in 1988 averaged 30.28 oz/person/week. With a population of about 57 million, the total domestic bread consumption would have been about 2.5 million tonnes per year, or about 2.75 million tonnes total consumption, allowing for about 10% consumed non-domestically. With about 45,000 t of vital gluten used in bread in the U.K. in 1988, the average level of use would have been about 1.6%. The usual rates of addition are 1.5% for white bread and 4.5% for wholemeal bread. In the U.S.A., about 70% of all vital wheat
WET MILLING: STARCH AND GLUTEN Cleaning stepit Germ Fibre Dr ying Wet screening extracti gnd grindin 「oxh Evaporating Crystallizing FIG. 12. 1. Maize wet-milling process.(Adapted from Anon. (1958)Food, 27: 291; Con in Indust th edn, Corn Industries Resarch Foundation Inc, New York, and S A. Matz(Ed (1970) Cereal Technology, Avi Publ. Co Inc. Westport, Conn. U.S.A.)
Cleaning Steeping Evaporating concentrates I 1 1 1 Moisture Grinding expelling Moisture expelling * Drying Filtering I I 011 extracting * Germ cake Feed drying and grinding Bleaching 1 Oil - Deodorizing Gluten feed Gluten meal
TECHNOLOGY OF CEREALS luten is used in the manufacture of bread, and more slowly to 43-45%. The steeping softens olls, buns and other yeast-raised products. The the kernel and assists separation of the hull, germ remainder finds uses in breakfast cereals(.g. and fibre from each other. The sulphur dioxide Kellogg s Special K), breadings, batter mixes and in the steep may disrupt the -ss- bonds in pasta products(Magnuson, 1985) the matrix protein (glutelin), facilitating starch protein separation. Gluten flour After steeping, the steep water is drained off Gluten flour is a blend of vital wheat gluten is protein. The protein in the steep water is with wheat flour, standardized to 40% protein recovered by vacuum evaporation, allowed to content in the u.s.a settle out of the water in tanks and dried as 'gluten feed' for animal feeding The water recovered is re-used as steep water or, after aize concentration, as a medium for the culture of Maize is wet-milled to obtain starch, oil, cattle organisms from which antibiotics are obtainee feed(gluten feed, gluten meal, germ cake)and the hydrolysis products of starch, viz. liquid and solid glucose and syrup De-germing The maize, after steeping, is coarsely ground in de-germing mills with the objective of freeing the germ from the remainder of the grain without The sequence of operations in wet milling of breaking or crushing the germ. The machine maize is shown in Fig. 12.1 generally used for this purpose is a Fuss mill,a For safe storage, maize must be dried because bronze-lined chamber housing two upright metal the moisture content at harvest is generally higher plates studded with metal teeth. One plate rotates than the desirable m.c. for storage. Drying at 900 rev/min, the other is stationary. Water and temperature should not exceed 54@C; at higher maize are fed into the machine, which cracks temperatures changes occur in the protein where- open the grain and releases the germ by addition by it swells less during steeping, and tends to of a starch-water suspension, the density of the hold the starch more tenaciously, than in grain ground material is adjusted to 8-10.5 Be*(1. 06- not dried or dried at lower temperatures. In 1.08 sp gr. at this sp. gr. the germs foat while addition, if dried at temperatures above 54C the the grits and hulls settle germ becomes rubbery and tends to sink in the ground maize slurry(whereas the process of germ separation depends on the floating of the germ), Germ separation and the starch tends to retain a high oil content The ground material flows down separating troughs in which the hulls and grits settle, while Steeping the germ overflows. More modern plants use hydrocyclones which require less space and are The cleaned maize is steeped at a temperature less costly to maintain than flotation equipment of about 50oC for 28-48 h in water containing Moreover, the germ separated on hydrocyclones 0. 1-0. 2% of sulphur dioxide. Steeping is carried is cleaner than that separated by flotation out in a series of tanks through which the steep The germ is washed and freed of starch on water is pumped counter-current. The moisture reels, de-watered in squeeze presses and dried on ontent of the grain increases rapidly to 35-40%, rotary steam driers. The dry germ is cooked by Baume Scale: a hydrometer scale on which 0 represents the sp, gr. of water at 12. 5.C and 10 the sp. gr. of a 10% solution of NaCl at 12.5 C, It is also known as the lunge
262 TECHNOLOGY OF CEREALS gluten is used in the manufacture of bread, and more slowly to 4345%. The steeping softens rolls, buns and other yeast-raised products. The the kernel and assists separation of the hull, germ remainder finds uses in breakfast cereals (e.g. and fibre from each other. The sulphur dioxide Kellogg's Special K), breadings, batter mixes and in the steep may disrupt the -SS- bonds in pasta products (Magnuson, 1985). the matrix protein (glutelin), facilitating starch/ protein separation. After steeping, the steep water is drained off. It contains about 6% of solids, of which 3545% Gluten flour Gluten flour is a blend of vital wheat gluten is protein. The protein in the steep water is with wheat flour, standardized to 40% protein recovered by vacuum evaporation, allowed to content in the U.S.A. settle out of the water in tanks, and dried as 'gluten feed' for animal feeding. The water recovered is re-used as steep water or, after Maize concentration, as a medium for the culture of Maize is wet-milled to obtain starch, oil, cattle organisms from which antibiotics are obtained. feed (gluten feed, gluten meal, germ cake) and the hydrolysis products of starch, viz. liquid and De-germing solid glucose and syrup. The maize, after steeping, is coarsely ground in de-germing mills with the objective of freeing the germ from the remainder of the grain without Operations The sequence of operations in wet milling of breaking or crushing the germ. The machine maize is shown in Fig. 12.1. generally used for this purpose is a Fuss mill, a For safe storage, maize must be dried because bronze-lined chamber housing two upright metal the moisture content at harvest is generally higher plates studded with metal teeth. One plate rotates than the desirable m.c. for storage. Drying at 900 rev/min, the other is stationary. Water and temperature should not exceed 54°C; at higher maize are fed into the machine, which cracks temperatures changes occur in the protein where- open the grain and releases the germ. By addition by it swells less during steeping, and tends to of a starch-water suspension, the density of the hold the starch more tenaciously, than in grain ground material is adjusted to 8-10.5" BC* (1.06- not dried, or dried at lower temperatures. In 1.08 sp.gr.): at this sp.gr. the germs float while addition, if dried at temperatures above 54°C the the grits and hulls settle. germ becomes rubbery and tends to sink in the ground maize slurry (whereas the process of germ Germ separation separation depends on the floating of the germ), and the starch tends to retain a high oil content. The ground material flows down separating troughs in which the hulls and grits settle, while the germ overflows. More modern plants use hydrocyclones which require less space and are Steeping The cleaned maize is steeped at a temperature less costly to maintain than flotation equipment. of about 50°C for 2848 h in water containing Moreover, the germ separated on hydrocyclones 0.1-0.2°/~ of sulphur dioxide. Steeping is carried is cleaner than that separated by flotation. out in a series of tanks through which the steep The germ is washed and freed of starch on water is pumped counter-current. The moisture reels, de-watered in squeeze presses and dried on content of the grain increases rapidly to 35-40%, rotary steam driers. The dry germ is cooked by * Baume Scale: a hydrometer scale on which 0" represents the sp. gr. of water at 12.5"C and 10" the sp. gr. of a 10% solution of NaCl at 12.5"C. It is also known as the Lunge Scale
ET MILLING: STARCH AND GLUTEN steam, and the oil extracted by hydraulic rotary or fash driers. Further fractionation to or by solvent extraction. The germ oil is so obtain the alcohol-soluble zein, which comprises filtered and stored The extracted germ about 50% of the maize gluten, by solvent extrac- used for cattle feed tion and precipitation may be carried out. Zein nds a use as a water-protective coating material for nuts and confectionery and as a binder for pharmaceuticals The de-germed underflow from the germ separ- A combined dry-wet milling process for refin ator is strained off from the liquor and finely ing maize has been described (U.S. Pat. N ground on impact mills, such as an entoleter, or 4, 181, 748; 1980) in which the maize is dry- milled attrition mills, such as the Bauer mill. After this to provide endosperm, germ, hull and cleaning process, the starch and protein of the endosperm fractions. The endosperm fraction is wet-milled are in a very finely divided state and remain inin two steps which respectively precede and suspension. The hulls and fibre, which are not follow an impact milling step. The principal reduced so much in particle size, can then be products are prime maize starch, corn oil and an separated from the protein and starch on reels animal feed product fitted with 18-20 mesh screens. Fine fibres which interfere with the subsequent separation of starch from protein, are removed on gyrating shaker Maize wet-milling in the U.s.A fitted with fine nylon cloth The processing of maize into wet-processed products has increased greatly in the U.S.A. in Separation of starch from protein recent years. In 1960/61, 3.94 Mt were processed rocessed products, but by 1984/85 the In the raw grain the starch granules are em- figure had increased to 20.7 Mt, representing bedded in a protein network which swells during 10.6% of the entire maize harvest in 1984 of 195 teeping stage and tends to form tiny globules Mt. Of this, 7.9 Mt were used to produce high of hydrated protein(Radley, 1951-1952). Disper- fructose corn syrup(HFCS),4.8 Mt for glucose sion of the protein, which frees the starch, is and dextrose, 3. 8 Mt for starch and 4.3 Mt for accelerated by the sulphur dioxide in the steep alcohol (Livesay, 1985). water The growth of the industry in the 1970s The effect of the sulphur dioxide, according to followed the development of a process to convert Cox et al.(1944), is due to its reducing, not to starch into high-fructose corn syrup(HFCS). The its acidic, property. The sulphur dioxide also has sweetness of hfcs allows it to be used as a a sterlizing effect, preventing growth of micro- substitute for sucrose in soft drinks and other organisms in the steep processed foods The suspension of starch and protein from the wet screening is adjusted to a density of 6 Be Products of wet-milling filters, and the starch separated from the protein The wet-milling of maize yields about 66% of in continuous high-speed centrifuges such as the starch, 4% of oil, and 30% of animal feed Merco centrifugal separator comprising about 24% of gluten feed of 21% The starch is re-centrifuged in hydrocyclones protein content(made up of about 13% of fibre to remove residual protein and is then filtered 7% of steep water solubles and 4% of germ and dried to 10-12% m.c. in kilns or ovens, or residue), plus about 5.7% of gluten meal of 60% in tunnel or fash driers. The moisture content is protein content. The composition of products further reduced by vacuum drying to 5-7%m c. from the wet-milling of maize is shown in table in the u.s.A., or to 1-2%m c. in Britain. 12. 1(Wright, in Watson and Ramstad, 1987 The separated protein is filtered and dried in most of the starch is further processed to make
WET MILLING: STARCH AND GLUTEN 263 steam, and the oil extracted by hydraulic presses rotary or flash driers. Further fractionation to or by solvent extraction. The germ oil is screened, obtain the alcohol-soluble zein, which comprises filtered and stored. The extracted germ cake is about 50% of the maize gluten, by solvent extracused for cattle feed. tion and precipitation may be carried out. Zein finds a use as a water-protective coating material for nuts and confectionery and as a binder for pharmaceuticals. Milling The de-germed underflow from the germ separ- A combined dry-wet milling process for refinator is strained off from the liquor and finely ing maize has been described (U.S. Pat. No. ground on impact mills, such as an entoleter, or 4,181,748; 1980) in which the maize is dry-milled attrition mills, such as the Bauer mill. After this to provide endosperm, germ, hull and cleaning process, the starch and protein of the endosperm fractions. The endosperm fraction is wet-milled are in a very finely divided state and remain in in two steps which respectively precede and suspension. The hulls and fibre, which are not follow an impact milling step. The principal reduced so much in particle size, can then be products are prime maize starch, corn oil and an separated from the protein and starch on reels animal feed product. fitted with 18-20 mesh screens. Fine fibres, which Maize wet-milling in the U.S.A interfere with the subsequent separation of starch from protein, are removed on gyrating shakers fitted with he nylon cloth. The processing of maize into wet-processed products has increased greatly in the U.S.A. in recent years. In 1960/61,3.94 Mt were processed into wet-processed products, but by 1984/85 the Separation of starch from protein In the raw grain the starch granules are em- figure had increased to 20.7 Mt, representing bedded in a protein network which swells during 10.6% of the entire maize harvest in 1984 of 195 the steeping stage and tends to form tiny globules Mt. Of this, 7.9 Mt were used to produce highof hydrated protein (Radley, 195 1-1952). Disper- fructose corn syrup (HFCS), 4.8 Mt for glucose sion of the protein, which frees the starch, is and dextrose, 3.8 Mt for starch and 4.3 Mt for accelerated by the sulphur dioxide in the steep alcohol (Livesay, 1985). water. The growth of the industry in the 1970s The effect of the sulphur dioxide, according to followed the development of a process to convert Cox et al. (1944), is due to its reducing, not to starch into high-fructose corn syrup (HFCS). The its acidic, property. The sulphur dioxide also has sweetness of HFCS allows it to be used as a a sterlizing effect, preventing growth of micro- substitute for sucrose in soft drinks and other organisms in the steep. processed foods. The suspension of starch and protein from the Products of wet-milling wet screening is adjusted to a density of 6"BC (1.04 sp.gr) by de-watering over Grinco or string filters, and the starch separated from the protein The wet-milling of maize yields about 66% of in continuous high-speed centrifuges such as the starch, 4% of oil, and 30% of animal feed, Merco centrifugal separator. comprising about 24% of gluten feed of 21% The starch is re-centrifuged in hydrocyclones protein content (made up of about 13% of fibre, to remove residual protein and is then filtered 7% of steep water solubles and 4% of germ and dried to 10-12O/0 m.c. in kilns or ovens, or residue), plus about 5.7% of gluten meal of 60% in tunnel or flash driers. The moisture content is protein content. The composition of products further reduced by vacuum drying to 5-7% m.c. from the wet-milling of maize is shown in Table in the U.S.A., or to 1-2% m.c. in Britain. 12.1 (Wright, in Watson and Ramstad, 1987). The separated protein is filtered and dried in Most of the starch is further processed to make