FERMENTATION (from Lat. fermentare, from fervere, to boil), the decomposition of complex organic material into substances of simpler composition under the influence of nitrogenous organic subsances called ferments. The meaning of the term has undergone con siderable change at different times in conse quence of the • progress of chemistry and biology. By the alchemists it was often used to describe any reaction accompanied by an ebullition of gas or effervescence, even when purely inorganic, but among older meanings that which comes nearest to its present signi fication has reference to its use to describe such familiar processes as the transformation of grape-juice into wine, the formation of alcohol from the saccharine fluids prepared from cereals, and the raising of dough in bread mak ing. Closer examination has shown that these processes are only a few out of many of a similar kind, and now all such processes are included under the name fermentation. In its present sense it may be defined as including all chemical changes brought about through the agency, immediate or at least apparently im mediate, of living micro-organisms or of organic substances immediately derived from the vegetable or animal kingdom, these sub stances remaining essentially the same after the reaction as they were before it, and adding nothing to the fermented substance. The or ganism or substance which produces the fer mentation is known as a ferment, and in ac cordance with the foregoing definition fer ments may be divided into two main groups, namely, (1) organized or formed ferments and (2) unorganized, unformed or soluble fer ments, usually called enzymes. Both kinds are nitrogenous organic bodies of somewhat un stable character, and in both cases the amount of ferment required to transform a given amount of the fermentable substance is rela tively very small. The organized ferments are, however, living bodies of microscopic size be longing to the groups of fungi and bacteria, and are therefore capable of growth and reproduc tion, while the enzymes are lifeless substances of definite chemical composition. The action of the enzymes, accordingly, is often separated from that of the organized ferments and not included under the term fermentation, but the present state of our knowledge does not seem to offer sufficient warrant for such a course.
The enzymes .or unorganized ferments play an important part in the vegetable and animal kingdoms. Thus, the solid, insoluble reserve materials stored up in the seeds, roots, under ground stems and other parts of plants are by their means transformed into soluble substances capable of being diffused throughout the plant body. These enzymes are of protoplasmic
origin, and are apparently complex compounds, some of them proteid, but not all. Diastase, the best known among them, is believed not to be proteid. The exact nature of their action is unknown, but all, or nearly all, produce their changes by a process known as hydrolysis, the nature of which may be best elucidated by cit ing a particular instance, the action of the enzyme invertase or invertin (see below) on cane-sugar. The molecule of cane-sugar under the influence of the ferment takes up a mole cule of water, which becomes fixed, that is, in corporated with it, and then the combination resolves itself into the two simpler sugars, dextrose and levulose. The equation is as follows: CuHnOn + H2O C.411.204. The enzyme remains apparently unchanged, and a very small quantity of it seems capable of transforming an indefinite amount of the sub stance on which it acts. In one case, however, it has been proved that the enzyme forms a compound with the fermentable substance, and that the final products, including the enzyme, are then produced by the solution of this com pound in water. This is probably the mode of action in all cases, and it is certainly much more intelligible than the former explanation by catalytic or contact action. The optimum temperature for most enzymes is between 85° and 120° F., (at 160° their activity ceases) and they are most active in the dark. The best known enzyme is diastase, which is present in malted grain and converts starch into maltose and dextrin. Other enzymes are invertase, al ready referred to; cytase, which acts chiefly on the cellulose of the cell-walls of grain and other seeds; inulase, which transforms inulin into levulose in various bulbs and tubers; emit. sin, which decomposes the glucoside amygdalin of many rosaceous plants into glucose, benzoic aldehyde and hydrocyanic acid; pepsin, found in gastric juice; trypsin, secreted by the pan creas; zymase, to which the alcoholic fermenta tion has been ascribed; and arose, to which the decomposition of urea into ammonium car bonate is primarily due—all of which actions are now regarded as fermentations. A further extension now under investigation regards miasmatic diseases, and virulent and contagious diseases, and the putrefaction of dead bodies as fermentations.