This section is from the book "Elements Of The Theory And Practice Of Cookery", by Mary E. Williams. Also available from Amazon: Elements Of The Theory And Practice Of Cookery; A Textbook Of Domestic Science For Use In Schools.
A. Make half a cup of flour into a very-stiff dough with a little water. Knead this several minutes on a very-fine strainer set in a bowl of water. Examine what is left in the strainer. How does it look? feel ? Spread some of it on a saucer to dry and examine it again. Heat some in the oven, notice how it swells. (See Plate VIII.)
B. Test the sediment in the water for starch in two ways.
Wheat-flour, when kneaded with water, yields a yellowish gray substance that when 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.
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. There is usually about twice as much gliadin as glutenin in good bread flour.
C. Test gluten for protein in two ways. (Pp. 86 and 151.)
The body of a wheat grain is largely starch and protein. The protein is mostly gluten. This central mass is called the endosperm. At one end of the grain is the germ. This is rich in fat and in tissue-building material both nitrogenous and mineral.
Around the outside of the grain is a layer, in some places a double layer, of large, square cells. These contain nitrogenous material (aleurone). This layer is generally removed in milling. Outside of it are five coats of bran which contain mineral matter, including phosphates. All these food stuffs are stored in cells with walls of cellulose, but there is more cellulose in the bran than anywhere else.
Fig. 8. - Cross-section of a wheat-grain, enlarged.
a and c = bran-coats; d = layer of aleurone cells; e = cells containing starch and gluten.