Human Foods and Their Nutritive Value, Harry Snyder [free e books to read TXT] 📗
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Fig. 39.—Exterior of Flour Mill and Wheat Elevator.
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.
Fig. 41.—Silk Bolting
Cloth Used in Manufacture
of Flour, Magnified.
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]
(N × 5.7) Fat Carbohydrates Ash Acidity
calcualted as
Lactic Acid Heat of
Combustion
Per Gram
Determined % % % % % % Calories First patent flour 10.55 11.08 1.15 76.85 0.37 0.08 4032 Second patent flour 10.49 11.14 1.20 76.75 0.42 0.08 4006 Straight[A] or standard patent flour 10.54 11.99 1.61 75.36 0.50 0.09 4050 First clear grade flour 10.13 13.74 2.20 73.13 0.80 0.12 4097 Second clear grade flour 10.08 15.03 3.77 69.37 1.75 0.56 4267 "Red dog" flour 9.17 18.98 7.00 61.37 3.48 0.59 4485 Shorts 8.73 14.87 6.37 65.47 4.56 0.14 4414 Bran 9.99 14.02 4.39 65.54 6.06 0.23 4198 Entire-wheat flour 10.81 12.26 2.24 73.67 1.02 0.32 4032 Graham flour 8.61 12.65 2.44 74.58 1.72 0.18 4148 Wheat 8.50 12.65 2.36 74.69 1.80 0.18 4140
[A] Straight flour includes the first and second patents and first clear grade.
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
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