Potatoes, for example, from which most of the starch of commerce is manufactured, after being pared, are grated to a pulp. This pulp is put upon a sieve and stirred about, while at the same time a little stream of water is made to flow upon it. A milky liquid runs through the sieve, but the fibrous portion of the potato, the vegetable tissue, remains behind. This liquid, after a short interval, deposits a white powder, which is the starch. By the simple process of tearing up the vegetable tissue, and removing the inclosed starch by washing, this substance may be procured from a great variety of plants.
Why do potatoes, beans, rice, and most of the common vegetables, swell up when boiled with water?
Because the starch absorbs water at the boiling temperature, which causes the cells to swell, thereby giving to the vegetable a rounded appearance.
What is the composition of wheat flour?
Starch is one of the principal constituents of wheat flour, as well as of all other kinds of meal. The other principal constituent is a gray, tough, viscous substance, called gluten.
To what does paste, made of wheat or rye flour, owe its adhesiveness?
In some measure to the starch, but principally to the gluten contained in it.
Can starch be converted into gum and sugar?
It can; fruits and plants effect this change naturally: we can also produce the change artificially by chemical processes.
Why are potatoes frozen and thawed sweet?