FERMENTATION. This is a general name for certain changes which occur in vege table and animal matters, and by which there are produced new fluids and gaseous com pounds. Fermentation is of three kinds the vinous, producing alcohol ; the aeetous, yielding vinegar ; and the putrefactive, of which the products are very variable, and usually fetid.
When the expressed juice of grapes is ex posed in warm weather to the air, it soon be comes turbid; its temperature rises a few de grees, a motion occurs in tho fluid, and minute bubbles of air form and break. As the process goes on, a thick froth, consisting of these bubbles and viscid matter, rises to the surface, and, when these bubbles have burst, a viscid substance falls to the bottom of the vessel ; this possesses the property of causing fermen tation to take place in other fluids which, with out its presence, would not undergo such a change : this substance is called vest. The sugar of the grape has undergone by this fer mentation a decomposition into alcohol and carbonic acid.
Although sugar yields alcohol by its decom position, yet pure sugar suffers no fermenta tion. In the juice of the grape, there is some accompanying matter which acts as a ferment; and when vest is thus spontaneously produced it causes fermentation in sugar, without, as far as appears, adding anything important.
The fermentation of malt-extract is noticed under BREWING and DISTILLATION. Acotous fermentation is treated under ACETIC Acm and VINEGAR. The putrefactive fermentation is the spontaneous decomposition of vegetable and animal matter, which is unaccompanied with the production of alcohol or acetic acid. In vegetable putrefactive fermentation the principal product is carbonic acid, and proba bly water, both derived from the absorption of the oxygen of the air, which unites with the hydrogen and carbon of the vegetable matter. In the putrefactive fermentation of animal matter ammonia is formed by the union of the hydrogen and nitrogen of the substance.