_Properties of starch._ Take a small quantity of the starch previously obtained from the flour and mix it with water until just milky. Place a drop of the starch water on a clean microscopic slide and put a cover glass over it and gently press it down. In placing the prepared slide under the microscope the starch cells are seen to be fairly round or slightly oval, of various sizes (Fig. 2). A little off the center a bitum is observed.
The “bitum” is a sort of nucleus or spot which is the center around which the concentric rings of starch are arranged.
If by chance some of the starch properties be resting on their narrow surface they will appear elongated. Each starch particle represents a cell. The interior of the cell contains the starch proper, and is surrounded by an external coating of very delicate fibrin or cellulose. In old samples of flour the starch shows cracks and fissures.
The starch of rye flour is but slightly different (Fig. 3), and is difficult to tell it apart from wheat starch. The particles of sound rye starch are a trifle larger.
The starch of potatoes (Fig. 4) has a peculiar pear-shaped formation with very distinct bitum and concentric rings.
The properties of the starches given should enable the baker or student with the aid of the microscope to detect any foreign starch which may have been added to flour as an adulterant.
Mix a little starch with water and divide the mixture equally in two beakers.
Heat one portion to the boiling point; the starch then forms with the water, a thick, gelatinous, somewhat semi-clear liquid. The boiling causes the interior of the cell to swell, thereby bursting the cellulose envelopes.
The structure of the starch cell has been completely disrupted. The starch becomes gelatinized.
In the other beaker after a little while the raw starch precipitates. It has completely separated itself in its original form from the water.
Upon stirring the contents of the beaker violently the starch grains do not lose their original character, but simply remain suspended for a time in the water.
When baking bread the gelatinization of the starch does not take place, because the albuminoids of the flour regulated by the heat envelopes the liberated starch after its cellulose cavern has become disrupted, and in consequence prohibits the gelatinization of the starch.