_Ordinary dry flour contains from 8 to 18 per cent of moisture, and averages 13 per cent._
B. _Gluten contents of flour._—Knead some wheat flour with water into a dough. Lay it aside under cover for fifteen minutes; then place it in a very fine sieve and let a stream of water flow over it, working the dough all the time, until the draining becomes clear, which should be retained for further testing.
There will remain on the sieve a yellowish gray tough mass.
This is the _gluten_ which imparts strength to the flour. _Good sound wheat flour contains 10 to 12 per cent. of gluten._
The gluten of wheat flour swells considerably in water, but is not soluble.
In the dry state it is horny and brittle.
When moist it soon ferments and quickly putrifies.
Gluten is classified as an albuminoid, but is not soluble in either a weak or concentrated acetic acid solution. When boiled in a soda solution it becomes partially soluble.
On account of this characteristic it is closely allied to those albuminoids known as fibrin, which is found in large proportions in animal blood. In contrast to blood-fibrin gluten may be said to be vegetable-fibrin.
The gluten of wheat flour is not a simple body, therefore not an element, but is composed of four varieties of albuminoids: vegetable albumin, vegetable casein, vegetable fibrin and gluten itself.
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.