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of wheat is the same for all latitudes, and that if these vary, the period of growth will vary in inverse proportion. In support of this position Cooke* collected the statistics given below.
Cooke found the number of heat units required to be approximately the same for different countries, i. e., about 8,500. Experiments conducted at Fargo, N. D., to verify this failed of their purpose, and gave approximately 6,500 heat units. The period of growth was about 100 days. Recent observations have shown that the number of heat units decreases when the growing period shortens. In general, the growing period is shortest in the coldest climate.
The Weight of Different Materials entering into an acre of the wheat crop is shown in the table given below. All weights are in pounds. The grain and straw are given as air dry material, which contains about 15 per cent of water.
WEIGHT OF MATERIALS IN AN ACRE OF WHEAT.
Grain of 6.600
Straw of 6 600
Total of potash phos-
8.55 14.10 27.60
72.42 31.62 12.75 28.05
1 Yearbook U. S. Dept. Agr., 1894, p. 174.
Chemistry.—The five outer layers of the wheat grain are composed chiefly of cellulose, a woody, fibrous substance. The endosperm, the food part of the grain, contains large quantities of starch, a nitrogenous substance known as gluten, a little sugar, and the cellulose of its cell walls. The gluten content is greatest at the hard exterior of the endosperm. The softer center makes better flour, however, for it remains freer from the bran in the grinding. The germ is composed of cellulose, nitrogenous substances, and about 10
per cent of fat. The following table gives in per cents of the entire weight the comparison of different kinds and commercial grades of wheat, and of wheat straw and chaff.
COMPARISONS OF GRADES OF WHEAT, WHEAT STRAW AND CHAFF.
310 Amer wheats, min!
8.1 17.2 11.9 17.2 17.9 18.3 20.7 20.3 17.3 16.6 18.9 13.0 12.8 13.5 13.2 10.7 2.6 2.9 5.0 3.4 2.0
1.3 3.9 2.1 2.4 2.5 2.3 2.4 2.1 2.8 2.3 2.7 1.5 2.5 1.2 2.8 2.5 1.6 0.8 1.8 1.3 1.5 1.4 5.9 5.9 4.5 4.5
9.3 16.5 14.4 10.9 12.5 10.5 9.5 6.4 6.5 17.9
9.6 14.3 14.3 10.9 10.4 11.5 11.8
2.2 2.4 2.2 1.9 2.0 2.2 2.0 1.4 1.7 1.7 3.6 10.5 3.0 7.0 4.2 5.5 12.0 5.3 4.1 5.4 4.6
4.5 12.3 14.4 16.1 14.9
3.4 3.2 3.2 2.3 2.5 2.5 2.5 3.0 2.0 2.7 2.6 10.8 37.9 34.3 42.7 38.1 48.0 36.0 10.8 6.1 8.0 7.4
1 U. S. Dept. Agr., Office Exp. Sta., Exp. Sta. Bul. 11, pp. 106-118. : N. D. Bul. 8, p. 6. Average results from many analyses.
3 Rept. N. D. Exp. Sta., 1903, p. 26. Data from N. D. wheat crop of 1901.
* Johnson, How Crops Grow, pp. 386-387.
5 Rept. Canada Exp. Farms, 1900, p. 182. 1899 crop grown in the N. W. Terrs.
& Church, Food Grains of India, p. 95.
? An average from Dak. Stations, U. S. Dept. Agr., Farm Bul. 139, p. 11.
& Rept. N. D. Exp. Sta.. 1904. p. 33
The substances of which wheat flour is composed may be divided into three classes: (1) Nitrogenous, which include mainly gluten, fibrin, albumen, casein, cerealin, and modifications of some of these; (2) non-nitrogenous, embracing sugar and dextrin, but chiefly starch, fat and cellulose; and (3) the minerals, for the largest part alkaline phosphates and silicates, especially phosphate and silicate of potash.
WATER.—Wheat ordinarily contains from 10 to 15 per cent of moisture. Changes in the moisture content of the air cause corresponding variations in wheat, and consequently in its weight. Usually such fluctuations in weight do not exceed 6 per cent, but they may be as much as 25 per cent, and an increase of 9 per cent in 24 hours has been observed. When wheat is shipped, especially if it is transported long distances, this may be a matter of great commercial importance. Wheat transported from the dry atmosphere of the inland of California to ordinary temperate regions will invariably gain from 5 to 15 per cent in weight. In a voyage from San Francisco to Liverpool, the increase in weight due to the moisture absorbed en route may be sufficient to pay all expense of transportation. Every portion of the wheat grain is so susceptible to influence from hydroscopic conditions that all of the products of wheat exhibit similar oscillations in weight. Two days equalized the moisture content in samples of flour varying from less than 8 to over 13 per cent.'
Ash.—Lawes and Gilbert observed the composition of the ash of wheat grown on unmanured ground during 20 years. The average results are given in the table below.'
Straw Ferric oxide
33.345 15.355 Soda
0.265 Phosphoric anhydride (P'O)
3.10 Sulphuric anhydride (S0')
100.015 100.485 1 Hunt, Cereals in Amer. (1904), p. 38: Mich. Bul. 191, p. 159-164. 2 Hunt, ('ereals in Amer. (1904) p. 39.
.... 100.00 100.00 There is great uniformity in the ash constituents of the grain of wheat when it is not subject to irregularities in ripening, and there is but slight deviation under normal variations in soil composition.
PROTEIN.-Osborne and Voorhees' recognized and investigated five proteids. Approximately they form the following per cent of the grain: A globulin, 0.65; an albumin, 0.35; a proteose, 0.30; gliadin, 4.25; and glutenin, 4.25. Gluten is composed of several nitrogenous compounds, chiefly gliadin and glutenin. Wheat bread owes its excellence to the peculiar properties of gluten, which makes it lighter and more digestible than bread made from the other cereals. The amount and quality of gluten determine the baking qualities of a flour. It is now claimed that 55 to 65 per cent of the total gluten should be in the form of gliadin. Hard wheats have a higher gluten content than soft wheats, and consequently yield better flour. Gluten generally forms from 12 to 14 per cent of the wheat grain. Dough washed with water will retain only the crude gluten. A short growing period or a season unfavorable to full maturity of the grain increases the amount of protein. The nitrogenous compounds are the most desirable part of the nourishment found in wheat, but they tend to give a yellowish tint to the bread, “against which fashion rebels,” for the vunnatural demand of the times” is for a starchy, snow white flour.
NITROGEN FREE EXTRACT.-This forms the larger portion of both grain and flour, and is composed very largely of starch, the amount of which is easily influenced by the irregularity of
Composition Influenced by Seasons and Fertilizers.—A favorable season seems to give a high weight per bushel, a large percentage of starch, and a low ash and nitrogen content. The following table gives the results of the observations of Lawes and Gilbert at Rothamsted.
1 Amer. Chem. Jour., 15:392-471. ? Hunt, Cereals in Amer. (1904), p. 43.
Composition as Affected by Light.-Light is essential for the formation of proteids. The following table shows the effect of differently colored glasses upon the nitrogen and albumen content of wheat.
Climate, soil and culture are also all factors that affect the chemical composition of wheat. They are treated more fully in subsequent chapters.
The Composition of Different Commercial Grades of wheat shows that the amounts of protein and ash decrease as the grade of wheat becomes higher, while the nitrogen free extract increases. Differences in protein, gluten or gliadin content do not seem to be an adequate basis, however, for the commercial grading of wheat. The grading seems to be based rather on the relative yield of first quality flour. The greater the weight of the kernel and the weight per bushel, the higher is the grade of the wheat.
Historically there has been little change in the chemical composition of wheat. It seems likely that the wheat of ancient Egypt did not differ more in composition from modern wheat of the same variety than one sample of modern wheat frequently differs from another.
1 Sci. Amer., 93 (1905): 508.