Fermentation

a composition or change brought about in vegetable or animal matter by the action of minute plants, or by certain active substances. The change of apple juice to hard cider, of grape juice to wine, sweet water to vinegar, malt to beer, starch to sugar, or sugar to alcohol is a process of fermentation. The souring of milk, the rancidity of butter, the formation of curds, the rising of dough, as well as the putrefaction of meat and the decay of vegetables are due to fermentation. Some of the fermenting agencies or ferments, as the yeasts, are microscopic fungi; others are bacteria; and others again, forming a class by themselves, as the diastase of the brewer and the pepsin of the gastric juice, are lifeless, though active chemical agencies. Within bounds, fermentation is not only useful but absolutely necessary in the world's economy. Without fermentation, animal and vegetable substances would not return to earth again. Fermentation may be prevented in several ways. In the first place, the germs of ferment may be excluded by canning, bottling, pickling, and other processes. It may be prevented by heat. A liquid maintained at the boiling point would not ferment in a thousand years. It may be prevented by cold. Frozen meats do not putrefy. The frozen carcass of a mammoth was found in Siberia, where it had lain for no one knows how long, probably thousands of years. Absence of moisture prevents fermentation. Dried beef keeps for a long time. The carcasses of animals that die in the Sahara dry up, and, unless torn to pieces by birds of prey, are preserved for an indefinite length of time. Alcohol, salt, an excessive quantity of sugar, and other agencies poison the germs of ferment and prevent decay. See Bacterium; Beer; Wine; Vinegar; Yeast, etc.