Book of American Baking / A Practical Guide Covering Various Branches of the Baking Industry, Including Cakes, Buns, and Pastry, Bread Making, Pie Baking, Etc.

by Various

A marked difference exists in the gluten of rye flour. It is difficult to wash it out. It forms a sticky gray mass and is composed of three varieties of albuminoids—vegetable albumin, vegetable casein and vegetable fibrin. Gluten itself is missing.

These three varieties of albuminoids are contained in much greater proportion than in wheat flour, but the total albuminous matter in both wheat and rye flour are contained in about equal proportions.

C. The starches of flour. The wash water which has been preserved from the gluten washing test will at first appear to be milky, but gradually becomes clarified. On the bottom of dish the starch which has come away from the flour with the wash water will be precipitated as a fine white powder.

The proportion of starch in both wheat and rye flour is almost equal. The average is 64 per cent. Fine or soft flour contains more starch than hard or coarse flour.

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.