FERMENTATION is the term applied to the change which occurs in one organic sub stance when influenced by another in a state of decay or putrefaction. The process was originally understood to include all the changes which matter of plant and animal origin undergoes when disunited from the living force, but is now restricted to certain of the changes. Thus, there are many substances, such as starch and sugar, which have no power of themselves to pass into decay, or change in composition through lengthened periods of time; whilst there is another class of substances, including albumen, fibrin, and caseine, as well as gelatinous tissues, mucus, etc., which, when exposed to moder ately heated air in a moist condition, more or less rapidly begin to putrefy or decom pose. The latter substances, viz., those which spontaneously pass into a state of change, are called ferments, and when they are brought into contact with sugar, etc., which other wise would not be altered, they cause the latter to be broken up into simpler com pounds; it is this process that constitutes fermentation. The ferment is always a body which has the power of rotting or becoming putrid, and is actually in a state of decom position. Every substance which is liable to putrefy becomes, while putrefying, a fer ment; and in this condition acquires the property of setting agoing the process of F. in any second body capable of it, and retains the power till it is so far decomposed that the putrescence is over. The ferments are very widely distributed in organic matter, and hence, whenever a plant or an animal dies, the process of F. proceeds more or less rapidly. The most important kind of F. is that known under the designation of 'vinous, and which forms part of the processes in the preparation of alcohol, beer, wine, etc. It consists in the action of a peculiar ferment called yeast (q.v.) upon a saccharine liquid, when the sugar is decomposed into two atoms of alcohol (each C411602), four atoms of carbonic acid (each and two atoms of water (each HO).
In this change it will be observed that the yeast, whilst it causes the change, does not unite directly or indirectly with any of the constituents of the sugar. The vinous F. proceeds best at a temperature ranging from 60° to 80° F., the mean and more desirable being about 70° F. The process itself causes the development of heat, and recourse must be had, therefore, to large airy rooms, where the fermenting tuns or vessels are arranged, and also to the circulation of cold water in pipes distributed round the interior of the vessels, and in contact with the liquid. See BEER.
The lactic acid F. takes place in milk when it begins to sour. The caseine of the milk acts the part of the ferment, and it causes the change in the sugar of milk, which is in part resolved into lactic acid + 110). The latter then curdles the caseine, and the milk besomes clotted. When the milk still further sours, and the material is kept at a temperature of 77° to 86° F., the butyric acid fermentation takes place, in which the putrefying caseine changes the sugar (q.v.) of milk into butyric acid + LEO).
The 'viscous or mucus F. occurs when the juice of the beet-root, dandelion, ash-tree, etc., is allowed to decompose at a temperature of 90° to 100° F., when the albuminous matter present causes the sugar to ferment into lactic acid, mannite, a gummy substance, some alcohol, and various gases. The same kind of F. occurs when boiled yeast or boiled gluten is added to ordinary sugar.
The remaining processes of F. are the benzoic F., yielding, amongst other matters, the essential oil of bitter almonds (q,v); the sinapic F., which occurs in mustard when moistened with water, and during which the pungent oil of mustard is developed; and the acetous F., which is, however, not a true instance of F., as the oxygen of the air is required to complete the change. See ACETIC ACID.