1. Potato starch or flour.
Potato starch is a white or faintly yellowish powder in which single, glistening granules can be seen by the naked eye. Under the microscope the granules appear mostly single with evident striae, usually with pointed ends containing the nucleus; they are also eccentric in structure. This starch rarely contains fragments of tissue. It is prepared by first treating finely divided pared potatoes with 1 percent dilute sulphuric acid, then washing, drying and grinding the starch.
2. Wheat starch.
Wheat starch can be obtained either from crushed wheat or from wheaten flour by treatment with water after the nitrogenous constituent, gluten, has been separated by kneading. It amounts to about 60-70 percent of the grain. Under the microscope the granules appear to differ considerably in size. They are distinguished from potato starch by the nearly central hilum, surrounded by faintly marked concentric striae, and again by the granules being more frequently adherent. Wheat flour rather than the starch is generally used in chocolate making.
3. Dextrin.
When starch is heated to between 200° and 210° C. it is converted chiefly into dextrin or starch gum with a little sugar. Dextrin is a white to yellowish and tasteless powder with a peculiar smell; it differs from starch in being readily soluble in water. It gives a reddish colour with an aqueous solution of iodine. Fehling’s solution is unaffected by dextrin in the cold, but on long continued heating it is reduced to red cuprous oxide.
4. Rice starch.
Rice starch is obtained from inferior kinds of rice and from rice waste by treatment with water. It appears under the microscope as small granules or oval bodies of various sizes. According to their position the granules always seem to be polygons,[142] formed by coalescence. It is thus easily distinguished from the previously mentioned starches.
5. Arrowroot.
Several kinds of starch, obtained from the tubers of various species of plants are commercially known under this name.