FERMENTATION. The word fermen tation, in general, is used to denote that change in the principles of organic bo dies, which begins to take place sponta neously as soon as their vital functions have ceased, and by them are at length reduced to their first principles. This has been distinguished into three stages, the vinous or spirituous, the acid or ace tous, and the putrid fermentation. It is ascertained almost beyond doubt, that the vinous fermentation takes place only in such bodies as contain saccharine juices. In this the most remarkable product is a volatile, colourless, slight inflammable fluid, which mixes with water in all pro portions, and is called alcohol, which see. The acetous fermentation is distinguished by the product known by the name of vinegar, which is the least destructible of the vegetable acids. It does not ap pear, however, that fermentation is abso lutely necessary for the production of this acid, as there are many other chemi cal processes by which it may be obtain ed or produced. In the putrid fermenta tion, bodies appear to be reduced into their most simple parts. Ammonia is the product which has been remarked as the chief of this process, and is no doubt produced by the combination of the hydrogen and nitrogen gases, which are disengaged together. See Ammo NIA.
The acetous, like the vinous fermen tation, is confined to vegetable sub. stances ; but the putrefactive process is most eminently perceived in animal bo dies. These either putrefy immediately ; or, if the putrefaction be preceded by either of the other stages, their duration is too Short to be perceived. It is con sidered as- an established fact, that the three stages of fermentation always fol low in the same order in such bodies as are susceptible of them all ; the vinous coming first, which is followed by the acetous and the putrefactive pro cesses.
The spontaneous decomposition of bo dies is retarded by extreme cold, by sud den drying of the parts or by preserva tion in closed vessels. The two first cir cumstances necessarily retard the chemi cal effects, by depriving the parts of that fluidity which is almost indispensably necessary in chemical processes. It will easily be understood that the third con dition will retard the spontaneous de composition of bodies, when it is consi dered that the atmosphere itself is the solvent, or at least the receptacle of many of the component parts of bodies with which it is disposed to unite. In well
closed vessels the parts of organized bo dies, which are disposed to fly off in the elastic state, are prevented from escaping; and such parts as might form new combi nations, by absorbing either the contents or the component parts of the atmos phere, are prevented, for want of a free communication. The three conditions for the accomplishment of fermentation are, therefore, fluidity or moisture, mo. derate heat, or a due temperature, and the access of air ; the fermentation will likewise be modified according to the various component parts of bodies.
In describing the vinous decomposition of vegetables, it will be of advantage to attend to that of mere sugar and water ; the phenomena in these being more dis tinct, because less modified by foreign admixture. If a considerable quantity of water, holding in solution about one third of its weight of sugar, be exposed to the air, at the temperature of about se venty degrees, after the addition of a small quantity of yeast, it soon under goes a remarkable change. In the course of a few hours the fluid becomes turbid and frothy ; oxygen is absorbed, bubbles of carbonic acid gas are disengaged, which rise to the surface and break. The disengagement becomes more and more abundant ; mucilage is separated, part of which subsides to the bottom ; and part being expanded into froth by the elastic fluid, forms yeast. During the course of several days, these effects gradually come to their height, and diminish again ; after which they proceed very slowly, but are long before they entirely cease. The fermented liquor has then no longer the sweet taste it had before, but becomes brisk and lively, with a pungent, spiritu ous flavour. Its specific gravity is also considerably less than before ; and when exposed to distillation it affords a light inflammable spirit. The quantity of this spirit, or alcohol, any fermented liquor will produce, is thought to follow some proportion of the change its specific gra vity undergoes in fermentation ; but the truth of this has not been clearly ascer tained. Wine, cider, and beer, are well known liquors of this kind.