Elements of the theory and practice of cookery

114 THEORY AND PRACTICE OF COOKERY moist is elastic and sticky like glue, and for this reason is called gluten. When dry it is horny and translucent. If moistened and heated, it expands to many times its original bulk. 206. Flour or gluten may be tested for nitrogenous sub- stances by mixing with it a few drops of nitric acid. How will the nitrogen show itself ? Strictly speaking, gluten does not exist in wheat or in dry wheat-flour. What we do find is a mixture of gliadin and glutenin, which, when kneaded with water, unite chemically to form gluten ; but since they are always found together, we may consider them together as gluten. 207. Composition of wheat. — Wheat owes its value as a tissue-builder to its gluten, which contains nitrogen. The body of the wheat grain is com- posed of starch and gluten ; the germ con- tains fat and tissue-building materials. Just beneath the bran coats are mineral salts. Fig. 11. — Cross-section of a wheat-grain, enlarged. valuable as a and c = bran-coats ; d = layer of alenrone cells ; e = cells boilC and UCrve containing starch and gluten. buildcrS ; the cell-walls consist of plant-fibre. Wheat also contains BREAD 115 208- — Microscopical examination of a wheat grain. — A. Pre- liminary.— Cut a wheat grain in two and draw the outline of its cut surface. B. Examine a mounted cross-section of a wheat grain. Ob- serve that it is the same shape as the cut surface of the grain you sliced in two. Look first at the mass of cells forming the body of the grain. These collectively are called the endosperm. They are full of starch and gluten. Are they larger or smaller than the starch cells in a potato? If the cross-section is taken from the near base of the grain, you may be able to find the germ or embryo, a little dark body near its centre. If so, notice how the cells of the endosperm seem to radiate from it. What is the use of the en- dosperm to the embryo? (§§ 146, 147.) Around the outside of the grain you will see a layer, in some places a double layer, of large, square cells. These contain tissue-building ma- terial (aleurone).^ This layer is generally removed ^ in milling. Outside of it are three coats of bran. C. Make a sketch from memory of the cross-section of the wheat grain. 1 These were formerly supposed to contain most of the gluten of the grain, hence they are incorrectly termed "gluten cells" in many books. Fig. 12. — Portion of a cross-section of a wheat grain greatly enlarged. b, and c = bran-coats ; (Z = layer of aleurone cells; e and / = cells containing- starch and gluten. 116 THEORY AND PRACTICE OF COOKERY The Manufacture of Flour 209. Cleaning. — If you ever visit a flour-mill you will first be shown the wheat as it is shovelled from cars into bins, mixed with other seeds, and with dirt, sticks, and nails. It is freed from these by being run through wire screens, scoured clean by revolving steel blades, and steamed slightly to soften its hard coats, before going to the rollers.