properties the gliadin of wheat. There is, however, in the rye no protein compound corresponding to the glutenin of wheat, and, therefore, rye flour does not form a gluten similar in quality to that of wheat, although it comes more nearly doing so than any other cereal. The gliadin of rye is soluble in alcohol, the leucosin of rye is soluble in water, and the edestin is soluble in a salt solution.

In a typical sample of American rye there will be found about 5.16 percent of gliadin, 2.27 percent of edestin and proteose, 0.55 percent of leucosin, and 3.14 percent of protein soluble in salt solution.

Adulteration of Rye Flour.-Rye flour is frequently adulterated by the admixture of flours of other cereals. Real rye flour is distinguished by the character of the starch granules, as shown in Fig. 31.

Rye starch grains are lenticular in form, and the largest grains are of about 50 microns diameter. They average somewhat larger than wheat starch grains and are characterized by many of the large grains having a fissure in the form of a slit, cross, or star, which is rare in wheat and barley. The rings and hilum are indistinctly seen in some of the grains.

Rye Bread. This bread may be made leavened or unleavened, since the analogy in the property of its protein to that of wheat renders the leavening of rye bread somewhat more easy of accomplishment than that of the other cereals, with the exception of wheat.

Rye bread made of pure rye flour has a dark color, sometimes almost black. It is often baked long in advance of the time of eating and keeps well, is highly nutritious, and is the staple bread of many European countries.

A partial rye flour bread is made by mixing rye flour with other flours, such as wheat, barley, Indian corn, etc., and this is the kind which is commonly used in this country and in many portions of Europe where the light-colored breads are preferred to the dark.

The large consumption of bread made from rye and Indian corn indicates that even if the supply of wheat should become limited there is no reason to fear a famine of bread. It would be easy to substitute bread made wholly or in part of Indian corn and rye for that made wholly of wheat and thus to supply practically any demand for bread which the increasing population of the earth may make.

WHEAT (GENUS Triticum).

In respect of human nutrition wheat is the most important of the cereals. It is grown in the temperate regions of almost every country, but does not flourish in tropical or subtropical countries.

In the United States the wheat is divided in respect of the period of its growth into two great classes, namely, winter or fall planted wheat and spring or spring planted wheat. Winter wheat is usually planted from September to November and spring wheat from the last of March to the last of April.

In this country wheat is not cultivated, that is, there is no cultivation of the soil after seeding. The soil is, however, plowed and harrowed before planting. In the winter wheat regions the harvesting is in the month of June, though in the southern localities it comes somewhat earlier and in the more northern localities may extend into July. In the spring wheat regions the harvesting is from the last of July to the middle or end of August. The statistics of wheat grown in the United States during 1906 are as follows:

All the different varieties of wheat which are now known are cultivated. The simplest form, namely, the one grain wheat is the only one which grows wild, and the origin of the other varieties of wheat is unknown.

Botanists recognize three species, namely Species 1, one grain wheat (Triticum monococcum Lam.); species 2, Polish wheat (Triticum polonicum L.); species 3, common wheat (Triticum sativum Lam.). All of these species are distinct, especially the third one, of which the most valuable variety is the common wheat, Triticum vulgare Vill.

The quality and properties of wheat depend more upon the environment in which it is grown than upon the species to which it belongs. There is perhaps no other field crop in which the environment, namely, condition of the soil, temperature, precipitation, etc., makes a greater difference than in wheat. In general, the environment and the species together produce two kinds of wheat as far as milling and bread making are concerned, namely, the soft or starchy wheat and the hard or glutinous wheat. In the first variety there is a larger percentage of starch in relation to the content or protein matter than in the second. Taking the wheat as a whole its average composition is shown in the following table:

In regard to protein American wheat, as a rule, is quite equal to that of foreign origin. This is an important characteristic when it is remembered that both the milling and food value of a wheat depend largely upon the nitrogenous matter which is present. It must not be forgotten, however, that merely a good percentage of protein is not of itself a sure indication of the milling value

of a wheat. The ratio of gluten to the other protein constituents in a wheat is not always constant, but it is the gluten content of a flour on which the bread making qualities chiefly depend.

Gluten. The principal part of the protein in wheat is known as gluten. Gluten as such does not exist in the wheat but is formed when the pulverized wheat, that is, the wheat flour, is mixed with water by the union of two elements in the wheat, namely, gliadin, which is soluble in dilute alcohol and forms nearly half of the whole protein matter of the wheat kernel, and glutenin, a compound insoluble in water, dilute salt solutions, and dilute alcohol and which is quite as abundant as gliadin in the wheat kernel. In fact, the gliadin and the glutenin together make the whole of the protein, except a little over one per cent.

There are three other forms of protein, as pointed out by Osborne, in the wheat kernel, making altogether nearly 1 percent of total protein content. The average quantity of these compounds in the protein of wheat is as follows. Constituents:

Starch in the Wheat Kernel.-The most abundant constituent of the wheat kernel is the starch. The appearance of wheat starch is shown in the figure. Wheat starch grains ordinarily show the rings and hilum in a few cases only under the most favorable conditions, though there are sometimes cases where the striations are quite distinct. The granules of starch vary greatly in size, being from 5 to 10 microns in diameter. There are, in fact, two kinds of granules in wheat starch, one having the appearance under the microscope of irregularly rounded particles in sections like a circular disk, and the other of elongated particles with a distinct hilum, as shown in Fig. 32. The appearance of the granules under polarized light is shown in Fig. 33.

Wheat starch is not very commonly used for commercial purposes but is highly prized for some things, especially in the sizing of textile fabrics. The germ in wheat is particularly rich in oil and the bran or outside covering in protein. The common idea that the bran is composed mostly of silicious matter is wholly erroneous. On the contrary the bran is a highly nutritious food, and the objection to it for human food is mostly of a mechanical nature.

Adulterations.-Wheat grains are never adulterated but they may sometimes contain dirt and foreign seeds, due to the growth of some body in connection with the wheat itself.

Standards. Wheat, commercially, is sold under three standards, namely,

one, two, three. The difference is an arbitrary one and not founded upon any chemical data but wholly upon the physical appearance, degree of moisture, and freedom from extraneous admixtures.

Wheat Products.-The principal product of wheat is flour. The milling process for wheat is highly interesting both from a chemical and technical point of view, but cannot be described in full in this manual. The old-fashioned milling of wheat, namely, pressing between stones and separation of the flour by bolting has been almost entirely superseded by the modern milling with metal rollers.

Altogether nearly a hundred different products are made incident or final

to the milling of wheat. Only those products, however, which are used for human food interest us at the present time.

Chief Varieties of Flour.-The highest grade of wheat flour is known usually by the term "patent"; a lower grade is known as "bakers' flour" and a third as low grade flour. A barrel of flour weighs 196 pounds and requires about 258 pounds of wheat for its manufacture. The whole product from the 258.35 pounds of wheat is shown in the appended table.

In general it may be said that about 75 percent of the weight of the wheat. is obtained as merchantable flour of some kind, about 60 to 70 percent being

SPECIAL NAMES OF FLOUR.

243

good grade or straight flour. About 24 percent of the weight of the wheat is obtained as cattle food and about 1 percent is lost during the process of manufacture.

Special Names of Flour.-In addition to the classification above mentioned other names are used in many commercial senses for flour. These additional

FIG. 33.-WHEAT STARCH UNDER POLARIZED LIGHT. X 200.-(Courtesy of Bureau of Chemistry).

names are "family," "red dog," "blended," gluten, etc. Many flours are also named after the name of the mill or locality or bear simply fanciful

names.

Graham Flour. This term was originally applied to the coarse, unbolted flour which was made by grinding the whole wheat. The name, therefore,