For general use, the most convenient form of bread is usually considered to be that made from wheat flour, raised or made light by some method of fermentation, although in point of nutritive value and healthfulness, it does not equal light, unfermented, or aerated bread made without the aid of chemicals.

THE PROCESS OF FERMENTATION.—­Fermentation is a process of decomposition, and hence more or less destructive to the substances subjected to its influence.  When animal and vegetable substances containing large amounts of nitrogenous elements are in a moist state and exposed to air, they very soon undergo a change, the result of which is decomposition or decay.  This is occasioned by the action of germs, which feed upon nitrogenous substances, as do the various species of fungi.  Meat, eggs, milk, and other foods rich in nitrogenous elements can be preserved but a short time if exposed to the atmosphere.  The carbonaceous elements are different in this respect.  When pure starch, sugar, or fat is exposed to the air in a moistened state, they exhibit the very little tendency to change or decay.  Yet if placed in contact with decomposing substances containing nitrogen, they soon begin to change, and are themselves decomposed and destroyed.  This communication of the condition of change from one class of substances to another, is termed fermentation.  If a fermenting substance be added to a watery solution containing sugar, the sugar will be changed or decomposed, and two new substances, alcohol and carbonic acid gas, are produced.

The different stages of fermentation are noted scientifically as alcoholic, acetous, and putrefactive.  The first is the name given to the change which takes place in the saccharine matter of the dough, which results in the formation of alcohol and carbonic acid gas.  This same change takes place in the saccharine matter of fruits under the proper with conditions of warmth, air, and moisture, and is utilized in the production of wines and fermented liquors.

In bread-making, the alcohol and carbonic acid gas produced during the fermentation, are formed from sugar,—­that originally contained in the flour and the additional quantity formed from starch during the fermenting process.  It is evident, therefore, that bread cannot be fermented without some loss in natural sweetness and nutritive value, and bread made after this method should be managed so as to deteriorate the material as little as possible.

If this fermentation continues long enough, the acetous fermentation is set up, and acetic acid, the essential element of vinegar, is formed and the dough becomes sour.  If the process of fermentation is very much prolonged, the putrefactive change is set up, and the gluten is more or less decomposed.