151. Use for Bread Making.—Wheat is particularly adapted to bread-making purposes because of the physical properties of the gliadin, one of its proteids. It is the gliadin which, when wet, binds together the flour particles, enabling the gas generated during bread making to be retained, and the loaf to expand and become porous. Wheat varies in chemical composition between wide limits; it may contain as high as 16 per cent of protein, or as low as 8 per cent; average wheat has from 12 to 14 per cent; and with these differences in composition, the bread-making value varies.

152. Winter and Spring Wheat Flours.—There are two general classes of wheat: spring wheat and winter wheat. The winter varieties are seeded in the fall, and the spring varieties, which are grown mainly in the Northwestern states, Minnesota, and North and South Dakota, and the Canadian Northwest, are seeded in the spring and mature in the late summer. Winter wheat is confined to more southern latitudes and regions of less severe winter, and matures in the early summer. There are many varieties of both spring and winter wheat, although wheats are popularly characterized only as hard or soft, depending upon the physical properties. The winter wheats are, as a rule, more soft and starchy than the spring wheats, which are usually corneous or flinty to different degrees. There is a general tendency for wheats to become either starchy or glutinous, owing to inherited individuality of the seed and to environment. There are often found in the same field wheat plants yielding hard glutinous kernels, and other plants producing starchy kernels containing 5 per cent less proteids. Wheats of low protein content do not make high-grade flour; neither do wheats of the maximum protein content necessarily make the best flour. For a more extended discussion of wheat proteids, the student is referred to Chapter XI.

153. Composition of Wheat and Flour.—In addition to 12 to 14 per cent proteids, wheat contains 72 to 76 per cent of starch and small amounts of other carbohydrates, as sucrose, dextrose, and invert sugar. The ash or mineral matter ranges from 1.7 to 2.3 per cent. There is also about 2 per cent fiber, 2.25 per cent ether extract or crude fat, and about 0.2 per cent organic acids.

Summary:

Composition of Wheat Flour

154. Roller Process of Flour Milling.—Flours vary in composition, food value, and bread-making qualities with the character of the wheat and the process of milling employed. Prior to 1870 practically all wheat flour was prepared by grinding the wheat between millstones; but with the introduction of the roller process, steel rolls were substituted for millstones.^[60] By the former process a smaller amount of flour was secured from the wheat, but with the present improved systems about 75 per cent of the weight of the grain is recovered as merchantable flour and 25 per cent as wheat offals, bran, and shorts^[61].

The wheat is first screened and cleaned, then passed on to the corrugated rolls, or the first break, where it is partially flattened and slightly crushed and a small amount of flour, known as the break flour, is separated by means of sieves, while the main portion is conveyed through elevators to the second break, where the kernels are more completely flattened and the granular flour particles are partially separated from the bran. The material passes over several pairs of rolls or breaks, each succeeding pair being set a little nearer together. This is called the gradual reduction process, because the wheat is not made into flour in one operation. More complete removal of the bran and other impurities from the middlings is effected by means of sieves, aspirators, and other devices, and the purified middlings are then passed on to smooth rolls, where the granulation is completed. The flour finally passes through silk bolting cloths, containing upwards of 12,000 meshes per square inch. The dust and fine dÉbris particles are removed at various points in the process. The granulation of the middlings is done after the impurities are removed, the object being first to separate as perfectly as possible the middlings from the branny portions of the kernel. If the wheat were first ground into a fine meal, it would be impossible to secure complete separation of the flour from the offal portions of the kernel.

Flour milling is entirely a mechanical process; the flour stock passes from roll to roll by means of elevators. According to the number of reductions which the middlings and stock undergo, the milling is designated as a long or a short reduction system; the term 4, 6, 8, or 10 break process means that the stock has been subjected to that number of reductions. With an 8-break system of milling, the process is more gradual than with a 4-break, and greater opportunity is afforded for complete removal of the bran. In some large flour mills, the wheat is separated into forty or more different products, or streams, as they are called, so as to secure a better granulation and more complete removal of the offals, after which many of these streams are brought together to form the finished flour. What is known as patent flour is derived from the reduction of the middlings, while the break flours are recovered before the offals are completely removed; hence they are not of so high a grade. No absolute definition can be given, however, of the term "patent flour," as usage varies the meaning in different parts of the country.

155. Grades of Flour.—Flour is the purified, refined, and bolted product obtained by reduction and granulation of wheat during and after the removal of the branny portions of the wheat kernel. It is defined by proclamation of the Secretary of Agriculture, under authority of an act of Congress, as: "Flour is the fine, sound product made by bolting wheat meal, and contains not more than thirteen and one half (13.5) per cent of moisture, not less than one and twenty-five hundredths (1.25) per cent of nitrogen, not more than one (1) per cent of ash, and not more than fifty hundredths (0.50) per cent of fiber."

Fig. 40.—Grinding Floor of Flour Mill, Russell-Miller Milling Co., Minneapolis, Minn.

Generally speaking, flour may be divided into two classes, high grade and low grade. To the first class belong the first and second patents and, according to some authorities, a portion of the straight grade, or standard patent flour, and to the second class belong the second clear and "red dog." About 72 per cent of the cleaned wheat as milled is recovered in the higher grades of flour, and about 2 or 3 per cent as low grades, a large portion of which is sold as animal food. The high grades are characterized by a lighter color, more elastic gluten, better granulation, and a smaller number of dÉbris particles. Although the lower grade flours contain a somewhat higher percentage of protein, they are not as valuable for bread-making purposes because the gluten is not as elastic, and consequently they do not make as good bread. If the impurities from the low grades could be further eliminated, it is believed that less difference would exist between high and low grade flours.

Various trade names are used to designate flours, as a 95 per cent patent, meaning that 95 per cent of the total flour is included in the patent; or an 85 per cent patent, when 85 per cent of all the flour is included in that particular patent. If all the flour streams were purified and blended, and only one grade of flour made, it would be called a 100 per cent patent. An 85 per cent patent is a higher grade flour than a 95 per cent patent.

156. Composition of Flour.—The composition of the different grades of flour made from the same wheat is given in the following table:^[62]

Composition, Acidity, and Heats of Combustion of Flours And Other Milled Products of Wheat

In the table it will be noted that there is a gradual increase in protein content from first patent to "red dog," the largest amount being in the "red dog" flour. Although "red dog" contains the most protein, it is by far the poorest flour in bread-making qualities, and in the milling of wheat often it is not separated from the offals, but is sold as an animal food. It will also be seen that there is a gradual increase in the ash content from the highest to the lowest grades of flour, the increase being practically proportional to the grade,—the most ash being in the lowest grade. The grade to which a flour belongs can be determined more accurately from the ash content than from any other constituent. Patent grades of flour rarely contain more than 0.55 per cent of ash,—the better grades less than 0.5 per cent. The more completely the bran and offals are removed during the process of milling, the lower the per cent of ash. The ash content, however, cannot be taken as an absolute guide in all cases, as noticeable variations occur in the amount of mineral matter or ash in different wheats; starchy wheats that have reached full maturity often contain less than hard wheats grown upon rich soil where the growing season has been short, and from such wheats a soft, straight flour may have as low a per cent of ash as a hard first patent flour. When only straight or standard patent flour is manufactured by a mill, all of the flour is included which would otherwise be designated first and second patents and first clear.

157. Graham and Entire Wheat Flours.—When the germ and a portion of the bran are retained in the flour, and the particles are not completely reduced, the product is called "entire wheat flour." The name does not accurately describe the product, as it includes all of the flour and only a portion of the bran, and not the entire wheat kernel. Graham flour is coarsely granulated wheat meal. No sieves or bolting cloths are employed in its manufacture, and many coarse, unpulverized particles are present in the product^[62].

158. Composition of Wheat Offals.—Bran and shorts are characterized by a high percentage of fiber, or cellulose. The ash, fat, and protein content of bran are all larger than of flour. The protein, however, is not in the form of gluten, but is largely albumin and globulins,^[16] which are mainly in the aleurone layer of the wheat kernel, and are inclosed in branny capsules, and consequently are in a form not readily digested by man.

Fig. 42.—Flour and Gluten.

1, flour; 2, dough; 3, moist gluten; 4, dry gluten.

The germ is generally included in the shorts, although occasionally it is removed for special commercial purposes. It is sometimes sterilized and used in breakfast food products. The germ is rich in oil and is excluded from the flour mainly because it has a tendency to become rancid and to impart to the flour poor keeping qualities. Wheat oil has cathartic properties, and it is believed the physiological action of whole wheat and graham bread is in part due to the oil. The germ is also rich in protein, mainly in the form of globulins and proteoses. A dough cannot be made of pure germ, because it contains so little of the gliadin and glutenin.

159. Aging and Curing of Flour.—Flours well milled and made from high-grade, cleaned wheat generally improve in bread-making value when stored in clean, ventilated warehouses for periods of three to six months^[9]. High-grade flour becomes drier and whiter and produces bread of slightly better quality when properly cured by storage. If the flour is in any way unsound, it deteriorates during storage, due to the action of ferment bodies. Wheat also, when properly cleaned and stored, improves in milling and bread-making value. Certain enzymic changes appear to take place which are beneficial. Wheats differ materially from year to year in bread-making value, and those produced in seasons when all the conditions for crop growth are normal do not seem to be so much improved by storing and aging, either of the wheat or the flour, as when the growing season has been unfavorable. When wheat is stored, specific changes occur in both the germ and the cells of the kernel; these changes are akin to the ripening process, and appear to be greater if, for any reason, the wheat has failed to fully mature or is abnormal in composition.

The flour yield of wheat is in general proportional to the weight per bushel of the grain, well-filled, heavy grain producing more flour than light grain.^[61] The quality of the flour, however, is not necessarily proportional to the weight of the grain. It is often necessary to blend different grades and types of wheat in order to secure good flour.

160. Macaroni Flour is made from durum wheat, according to Saunders a variety of hard, spring wheat. It is best grown in regions of restricted rainfall. Durum and other varieties of hard spring wheat grown under similar conditions, differ but little in general chemical composition, except that the gluten of durum appears to have a different percentage of gliadin and glutenin, and the flour has a more decided yellow color. Durum wheats are not generally considered as valuable for bread making as other hard wheat. They differ widely in bread-making value, some being very poor, while others produce bread of fair quality.^[68]

161. Color.—The highest grades of flour are white in color, or of a slight creamy tinge. Dark-colored, slaty, and gray flours are of inferior quality, indicating a poor grade of wheat, poor milling, or a poor quality of gluten. Flours, after being on the market for a time, bleach a little and improve to a slight degree in color. Color is one of the characteristics by which the commercial value of flour is determined; the whiter the flour, the better the grade, provided other properties are equal^[9]. The color, however, should be a pure or cream white. Some flours have what is called a dead white color, and, while not objectionable as far as color is concerned, they are not as valuable for bread-making and general commercial purposes. One of the principal trade requirements of a flour is that it possess a certain degree of whiteness and none of the objectionable shades mentioned.

To determine the color of a flour, it is compared with a standard. If it is a winter wheat flour, one of the best high-grade winter patents to be found on the market is selected, and the sample in question is compared with this; if it is a spring wheat patent flour, one of the best spring wheat patent grades is taken as the standard. In making the comparison, the flours should be placed side by side on a glass plate and smoothed with the flour trier, the comparison being made preferably by a north window. Much experience and practice are necessary in order to determine with accuracy the color value of a flour.

162. Granulation.—The best patent grades of flour contain an appreciable amount of granular middlings, which have a characteristic "feel" similar to fine, sharp sand. A flour which has no granular feeling is not usually considered of the highest grade, but is generally a soft wheat flour of poor gluten. However, a flour should not be too coarsely granulated. The percentage amounts of the different grades of stock in a flour can be approximately determined by means of sieves and different sized bolting cloths. To test a flour, ten grams are placed in a sieve containing a No. 10 bolting cloth; with a camel's-hair brush and proper manipulation, the flour is sieved, and that which passes through is weighed. The percentage amount remaining on the No. 10 cloth is coarser middlings. Nearly all high-grade flours leave no residue on the No. 10 cloth. The sifted flour from the No. 10 cloth is also passed through Nos. 11, 12, 13, and 14 cloths^[63]. In this way the approximate granulation of any grade of flour may be determined, and the granulation of an unknown sample be compared with that of a standard flour. In determining the granulation of a flour, if there are any coarse or discolored particles of bran or dust, they should be noted, as it is an indication of poor milling. When the flour is smoothed with a trier, there should be no channels formed on the surface of the flour, due to fibrous impurities caught under the edge of the trier. A hand magnifying glass is useful for detecting the presence of abnormal amounts of dirt or fibrous matter in the flour.

163. Capacity of Flour to absorb Water.—The capacity of a flour to absorb water is determined by adding water from a burette to a weighed amount of flour until a dough of standard consistency is obtained. Low absorption is due to low gluten content. A good flour should absorb from 60 to 65 per cent of its weight of water. In making the test, it is advisable to determine the absorption of a flour of known baking value at the same time that an unknown flour is being tested. Flours of low absorption do not make breads of the best quality; also there are a smaller number of loaves per barrel, and the bread dries out more readily.

164. Physical Properties of Gluten.—The percentages of wet and dry gluten in a flour are determined as outlined in Experiment No. 27. Flours of good character should show at least 30 per cent moist gluten and from 10 to 12 per cent dry gluten. The quality of a flour is not necessarily proportional to its gluten content, although a flour with less than 10½ per cent of dry gluten will not make the best quality of bread, and flours with excessive amounts are sometimes poor bread makers. The color of the gluten is also important; it should be white or creamy. The statements made in regard to color of flour apply also to color of the gluten. A dark, stringy, or putty-like gluten is of little value for bread-making purposes.^[64] In making the gluten test, it is advisable to compare the gluten with that from a flour of known bread-making value. Soft wheat flours have a gluten of different character from hard wheat flours.

165. Gluten as a Factor in Bread Making.—The bread-making value of a flour is dependent upon the character of the wheat and the method of milling. It is not necessarily dependent upon the amount of gluten, as the largest volume and best quality of bread are often made from flour of average rather than maximum gluten content. But flours with low gluten do not produce high-grade breads. When a flour contains more than 12 or 13 per cent of proteids, any increase does not necessarily mean added bread-making value. The quality of the gluten, equally with the amount, determines the value for bread-making purposes.

166. Unsoundness.—A flour with more than 14 per cent of moisture is liable to become unsound. High acidity also is an indication of unsoundness or of poor keeping qualities. The odor of a sample of flour should always be carefully noted, for any suggestion of fermentation sufficient to affect the odor renders the flour unsuited for making the best bread. Any abnormal odor in flour is objectionable, as it is due to contamination of some sort, and most frequently to fermentation changes. A musty odor is always an indication of unsoundness. Some flours which have but a slight suggestion of mustiness will, when baked into bread, have it more pronounced; on the other hand, some odors are removed during bread making. Flours may absorb odors because of being stored in contaminated places or being shipped in cars in which oil or other ill-smelling products with strong odors have previously been shipped. Unsoundness is often due to faulty methods in handling, as well as to poor wheat, or to lack of proper cleaning of the wheat or flour.

167. Comparative Baking Tests.—To determine the bread-making value of a flour, comparative baking tests, as outlined in Experiment No. 29, are made; the flour in question is thus compared as to bread-making value with a flour of known baking quality. In making the baking tests, the absorption of the flour, the way in which it responds in the doughing process, and the general properties of the dough, are noted. The details should be carried out with care, the comparison always being made with a similar flour of known baking value, and the bread should be baked at the same time and under the same conditions as the standard. The color of the bread, the size and weight of the loaf, and its texture and odor, are the principal characteristics to be noted.

Fig. 44.—Comparative Baking Tests.

The quality of flour for bread-making purposes is not strictly dependent upon any one factor, but appears to be the aggregate of a number of desirable characteristics. The commercial grade of a flour can be accurately determined from the color, granulation, absorption, gluten and ash content, and the quality of the bread. Technical flour testing requires much experience and a high degree of skill.

168. Bleaching.—In the process of manufacture, flours are often subjected to air containing traces of nitrogen peroxide gas, generated by electrical action and resulting in the union of the oxygen and nitrogen of the air. This whitens and improves the color of the flour. Bleached flours differ neither in chemical composition nor in nutritive value from unbleached flours, except that bleached flours contain a small amount (about one part to one million parts of flour) of nitrite reacting material, which is removed during the process of bread making. The amount of nitrites produced in flour during bleaching is less than is normally present in the saliva, or is found naturally in many vegetable foods, or in smoked or cured meats, or in bread made from unbleached flour and baked in a gas oven where nitrites are produced from combustion of the gas. The bleaching of flour cannot be regarded as in any way injurious to health or as adulteration, and a bleached flour which has good gluten and bread-making qualities is entirely satisfactory. It is not possible to successfully bleach low-grade flours so they will resemble the high grades, because the bran impurities of the low grades blacken during bleaching and become more prominent. Alway, of the Nebraska Experiment Station, has shown that there is no danger to apprehend from over-bleaching, for when excess of the bleaching reagent is used, flours become yellow in color^[65]. Similar results have been obtained at the Minnesota Experiment Station. As bleaching is not injurious to health, and as it is not possible through bleaching to change low grades so as to resemble the patent grades, bleaching resolves itself entirely into the question of what color of flour the consumer desires. Pending the settlement of the status of bleaching the practice has been largely discontinued.

169. Adulteration of Flour.—Flour is not easily adulterated, as the addition of any foreign material interferes with the expansion and bread-making qualities and hence is readily detected. The mixing of other cereals, as corn flour, with wheat flour has been attempted at various times when wheat commanded a high price, but this also is readily detected, by microscopic examination, as the corn starch and wheat starch grains are quite different in mechanical structure. Such flours are required to be labeled, in accord with the congressional act of 1898, when Congress passed, in advance of the general pure food bill, an act regulating the labeling and sale of mixed and adulterated flours. Various statements have been made in regard to the adulteration of flour with minerals, as chalk and barytes, but such adulteration does not appear to be at all general.

170. Nutritive Value of Flour.—From a nutritive point of view, wheat flour and wheat bread have a high value.^[66] A larger amount of nutrients can be secured for a given sum of money in the form of flour than of any other food material except corn meal. According to statistics, the average per capita consumption of wheat in the United States is about 4½ bushels, or, approximately, one barrel per year, and from recent investigations it would appear that the amount of flour used in the dietary is on the increase. According to the Bureau of Labor, flour costs the average laborer about one tenth as much as all other foods combined, although he secures from it a proportionally larger amount of nutritive material than from any other food.

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