These occur as food materials in several forms. Cornstarch is the starchy portion only removed from the grain of corn. Wheat starch is more largely used for laundry purposes than for food. Rice flour may be treated as starch in cooking. Arrowroot is a fine starch from the roots of a family of plants growing in the West Indies and other warm climates. It is used principally in cooking for invalids. Cassava, manioca, tapioca, and sago are starchy materials in granular form. The first three are made from the pith of the cassava plant, the sago from the sago palm. The pure starches are all easily digested and inexpensive. Corn starch is the most abundant and cheapest pure starch in this country.
To understand the behavior of materials like cornstarch, rice flour, and arrowroot in cooking, we need to know more of the starch grain. Cornstarch is composed of myriads of tiny granules somewhat like those pictured in Fig. 39, but smaller. The starch granules of different plants differ in size and even in shape, but they all have a covering lying in folds, the pure starch being within. The granule unfolds or bursts when exposed to heat. When these granules are floating in water, and, being heated, open at the same moment, the starch paste is smooth; otherwise, the starch lumps.