Fermentation (Lat. fermentum, leaven, a contraction of fervimentum, from fervere, to boil), the conversion of an organic substance into one or more new compounds, under the influence of a body which is called a ferment. It is a process which with more or less skill has been employed from the earliest times in the manufacture of alcoholic beverages, but its philosophy has been but imperfectly understood until recent times, and several questions still remain involved in doubt, and are matters of warm controversy. Formerly chemists recognized four kinds of fermentation, the vinous, the panary, the acetous, and the putrefactive; but now the panary is included in the vinous, while other kinds have been added, the number not being definitely settled. The following list may be given as the one usually recognized, although it will be seen that some of them are probably parts of the processes of others: 1, saccharine; 2, alcoholic or vinous; 3, acetic; 4, lactic; 5, butyric; 6, mucous or viscous; 7, putrefactive. To these there might be added without impropriety the benzoic, in which the amygdaline of the bitter almond, under the influence of emulsine, forms prussic acid and other bodies; and the sinapic, in which oil of mustard is produced during fermentation of the flour of black mustard.

The act of digestion may also not improperly be regarded as a species of fermentation, because it involves, under the influence of minute organic cells, furnished by the mucous coat of the stomach, a transformation of proteine compounds into albuminose, which is just as truly a change by the influence of a ferment as the formation of lactic acid from lactic sugar, or of glucose from dextrine.-1. Saccharine Fermentation. In the article Brewing is described the process for the malting of barley, in which the production of diastase from albuminous matter accompanies the evolution of the grain into plumula and radicle. This diastase is the ferment of saccharine fermentation, by whose influence the starch of the grain is converted into sugar; the steps in the process being, first, the formation of soluble starch, then dextrine or gum, which next passes into glucose or grape sugar. Starch, soluble starch, and dextrine have the same chemical constitution, or more strictly speaking have the same proportion of elements, and may therefore be considered as allotropic conditions of each other.

The transformation of dextrine into glucose consists in the assimilation of the elements of water, and may be represented in the following equation:

C6H10O5

+

H2O

=

C6.H12O6

Dextrine.

Water.

Glucose.

There is usually at the same time produced a small quantity of lactic acid, in consequence of a catalytic action, probably of the diastase, by which the glucose, having the same proportion of elements as lactic sugar, but differently grouped, takes on the functions of the latter substance and splits up into lactic acid. The saccharine fermentation, which takes place in malting, is promoted by the action of heat, which should commence at about 85° and terminate at about 135° F.; but in a decoction of malt, as in the mash tun of the brewer, it is conducted at a higher temperature, from 158° to 167°. The drying of the malt in kilns at this stage arrests the conversion of the sugar into lactic acid, which is evolved in considerable quantity if the malt is allowed to cool in a moist state. The action of dilute acids, assisted by heat, also has the power of converting starch into dextrine and grape sugar. (See Dextrine.) -2. Alcoholic or Vinous Fermentation. If a decoction of malt is allowed to stand for a time in the open air at a temperature varying from 40° to 85° F., a change takes place, in which bubbles of carbonic acid gas may be seen to rise from the mass; and upon examination it will be found that portions of the sugar and gluten have disappeared, and in their place will be found alcohol, lactic, acetic, and succinic acids, and some glycerine, in varying proportions, depending upon the temperature and the amount of saccharification that had taken place in the malt.

There will also be found more or less of a viscous substance containing yeast cells and germs and other microscopic organisms, and some mannite. If, however, instead of allowing the decoction of malt to ferment spontaneously, it be kept at a temperature of 158° to 167° F. until most of the dextrine has been converted into glucose, and then filtered and cooled to 70° or 85° with sufficient rapidity to prevent the commencement of premature fermentation, and then a quantity of brewer's yeast which has been kept in a warm place until it begins to decay be stirred in the mass, brisk fermentation will soon be induced, by which nearly all the glucose will be transformed into alcohol and carbonic acid, as represented in the following equation:

C6H12O6

=

2C2H6O

+

2CO2

Glucose.

Alcohol.

Carbonic acid.

Under the most favorable circumstances not more than 95 per cent. of the sugar passes into alcohol and carbonic acid, the remainder being converted into succinic acid and glycerine. Both these bodies are formed, according to Pasteur, as follows:

49C6H12O6

+

30H2O

=

12C4H6O4

+

72C3H8O3

+

30CO2

Glucose.

Water,

Succinic acid.

Glycerine.

Carb. acid.

The production of succinic acid in alcoholic fermentation was discovered by C. Schmidt in 1847. Pasteur discovered a few years ago that glycerine was also one of the products. Amylic alcohol or fusel oil is also frequently produced in alcoholic fermentation. Cane sugar, C12H22 On, does not pass into alcohol and carbonic acid directly, but is first converted into glucose by assimilating one equivalent of water, thus:

C12H22O11

+

H2O

=

2C6H12O6

Cane sugar.

Water.

Glucose.

It then passes into alcohol and car-bonic acid as before represented. Milk sugar, C12H24O12, which has the same proportion of elements as grape sugar, but with a different molecular arrangement, is also transformed into alcohol and carbonic acid under the influence of cheese or other proteine bodies in a state of decay; first passing, according to some observers, into glucose. Must of grape or juice of fruit, if boiled and suspended in a bladder in the midst of fermenting must or wort, will not ferment; and it has been stated that if yeast cells be prevented from coming in contact with the fermentable liquid, fermentation will not take place, although the soluble contents of the cells may pass through the membrane. Should this statement be substantiated by further observation, it would go to show that the exceedingly minute germs of yeast cannot penetrate through the coats of animal membranes, although so small as to be scarcely visible under a magnifying power of 2,800 diameters, and would also show that fermentation, whatever may be the question as to its being itself a vital process or a chemical one, cannot take place without the influence of these vitalized germs.