Later came the shortened cake and still later the fermented loaf.
Bread is usually made from wheat, but rye or corn may be used, though they need to be mixed with wheat flour to give the best results.
Bread flour may be white, whole wheat or entire wheat and graham, according to the process of milling used. Graham consists of the entire kernel and differs from the whole wheat in that it contains all of the bran. The whole wheat flour is made from wheat from which the outer part of the bran has been removed. White flour is made from that portion of the wheat kernel which lies beneath the bran.
For most people the whole wheat and graham breads are more wholesome, as the bran is valuable for the bulk which it produces.
Breads are of two classes, viz., the fermented and un-fermented.
Unfermented bread is made light by the action of the ferment yeast, a microscopic plant which grows and multiplies very rapidly under favorable conditions.
The conditions necessary for its growth are warmth, moisture and food.
The yeast plant was originally a "wild" yeast such as that which accompanies almost every particle of dust and which operates in the spoiling of fruits and other foods. Undoubtedly the first leavened bread was made from this variety of yeast.
The growing of yeast for bread making has become of sufficient importance commercially that it is now cultivated in much the same way that other plants are grown for the market. Great care is taken not to allow the cultures to become contaminated.
It is generally put upon the market in the form of dried cakes or of compressed cakes.
The compressed cakes are moist and spoil quickly. They contain the yeast plant in an active growing condition, while the dried cakes contain the yeast chiefly in the form of spores and must be nursed back, as it were, into the growing state by supplying the conditions necessary for growth, namely the moisture, warmth and food, hence it is necessary when using the dried yeast cakes to soak them and start the bread in the form of sponge.
Compressed yeast acts more quickly and can be made up into dough instead of the sponge.
The yeast plant grows best at a temperature of about 98° F., hence it is important that all the materials should be warmed. The flour may be warmed by setting in an open oven for a half hour or more and stirring occasionally.
The food which yeast likes best is sugar produced from the starch of the flour by the action of the diastase, the natural ferment which digests starch in the plant world. The diastase begins to act when moisture and warmth are present.
Bread is best made from spring wheat flour, as it contains more gluten than the winter wheat. The gluten gives firmness and elasticity to the loaf.
When the yeast feeds upon the sugar formed from the starch, it breaks it down into carbon dioxide gas and alcohol. The carbon dioxide gas produces the lightness of the bread and is therefore desirable. The gluten of the flour envelops the bubbles of carbon dioxide, making a porous mass. The first kneading is for the purpose of distributing the yeast through the dough. The later kneadings are for the purpose of distributing the bubbles of carbon dioxide equally through the mass. The alcohol, being volatile, is driven off in the baking of the bread.
The baking is chiefly for three purposes, first, the killing of the yeast plant; secondly, the changing of the starch from an insoluble to a soluble form; third, the expansion of the gas, carbon dioxide, thus increasing the lightness of the loaf.