To induce fermentation, a portion of some nitrogenous body, itself undergoing decomposition, must be added. Yeast consists of vegetable egg-shaped cells, which is increased during its action as a ferment. In order that fermentation shall begin we require, besides the contact of the ferment, the presence of air. The most easily decomposed articles of food may be preserved for an indefinite period by hermetically sealing them in jars, after drawing out the air. When once begun, however, fermentation will go on, if the air be excluded.
Temperature is important.
The most favorable temperature is between 68 and 77 Fahr. At a low temperature fermentation is exceedingly slow. A boiling heat instantly stops fermentation, by killing the ferment. To check fermentation we may remove the yeast by filtration. Too much sugar is unfavorable to fermentation, the best strength for the syrup is ten parts of water to one of sugar.