FEN′UGREEK. The seeds of Trigonella Fœnum Græcum. Resolvent and stomachic. The seeds dye yellow; formerly roasted for coffee; now chiefly employed in veterinary medicine.
FER′MENT. Syn. Fermentum, L. A substance which induces fermentation. According to one view ferments are compounds whose decomposition proceeds simultaneously with that of the body undergoing metamorphosis. They all contain albuminous or azotised principles, which in a moist state putrefy and suffer decomposition. According to Pasteur, however, fermentation is excited by living organisms—fungi and infusoria. See Fermentation and Yeast.
FERMENTA′TION. Syn. Fermentatio, L. In chemistry, a peculiar metamorphosis of a complex organic substance, by a transposition of its elements under the agency of an external disturbing force. Fermentation, according to the theory proposed by Liebig, is a metamorphosis, by which the elements of a complex molecule group themselves so as to form more intimate and stable compounds. It is excited by the contact of all bodies the elements of which are in a state of active decomposition or fermentation. “In nitrogenised substances of a very complex constitution, putrefaction or fermentation is spontaneously established when water is present, and the temperature sufficiently high, and it continues till the original compounds are wholly destroyed. Substances destitute of nitrogen, on the contrary, require, in order to their undergoing this metamorphosis, the presence of a nitrogenised substance, already in a state of putrefaction (fermentation).” (Liebig.) The substances which promote this change are termed FERMENTS, and among these the principal are gliadin, gluten, vegetable albumen, and all nitrogenous substances in a state of spontaneous decomposition or fermentation. “It is imagined that when these substances, in the act of undergoing change, are brought into contact with neutral ternary compounds of small stability, as sugar, the molecular disturbance of the body, already in a state of decomposition, may be, as it were, propagated to the other, and bring about the destruction of the equilibrium of forces to which it owes its being. The complex body, under these circumstances, breaks
up into simpler products, which possess greater permanence.” (Fownes.) Yeast, the ferment most commonly employed for inducing the vinous fermentation, is such a substance in an active state of putrefaction, and whose atoms are in continual motion. Putrefying animal substances are equally capable of exciting the same action. “If we add to a solution of pure sugar an albuminous substance, a caseous or fleshy matter, the development of yeast becomes manifest, and an additional quantity of it is found at the end of the operation. Thus, with nourishment, ferment engenders ferment. It is for this reason that a little fermenting must, added to a body of fresh grape juice, excite fermentation in the whole mass. These effects are not confined to alcoholic (vinous) fermentation. The smallest portion of sour milk, of sour dough, or sour juice of beet-root, of putrefied flesh and blood, occasions like alterations in fresh milk, dough, juice of beet-root, flesh, and blood. But further, and which is a very curious circumstance, if we put into a liquid containing any fermenting substance another in a sound state, the latter would suffer decomposition under the influence of the former. If we place urea in the presence of beer-yeast, it experiences no change; while if we add it to sugar-water in a fermenting state, the urea is converted into carbonate of ammonia. “We thus possess two modes of decomposition; the one direct, the other indirect.” (Ure.)
A very remarkable circumstance connected with fermentation is that it is always accompanied by the development of microscopic living organism—fungi and infusoria. “So constantly, indeed, is this the case, that many chemists and physiologists regard these organisms as the existing cause of fermentation and putrefaction; and this view appears to be corroborated by the fact that each particular kind of fermentation takes place most readily in contact with certain living organisms.” (Fownes.) Thus the vinous or alcohol-producing fermentation is accompanied, or caused, by two fungi, called Torula cerevisiæ and Penicillium glaucum; the acetous or vinegar-producing fermentation by Torula aceti; the lactous fermentation (souring of milk) by Penicillium glaucum.
The butyric fermentation by an animal—an infusorium, which cannot exist in free oxygen, but flourishes in an atmosphere of hydrogen, &c.
Of late years these latter views as to the cause of fermentation have been accepted by most of the scientific world, notwithstanding the opposition they experienced from so powerful an antagonist as Liebig.
From the researches of Pasteur, the distinguished author of the modern theory of fermentation, as opposed to the chemico-physical theory of Liebig, it appears that when yeast is placed in a solution of sugar and water, or in a solution of sugar and water containing albuminous substances, under proper conditions as to temperature, the fermentation that ensues is due to the process of growth taking place in the yeast plant; the new cells of which, in assimilating part of the sugar and converting it into cellulose and fat, cause, at the same time, the breaking up of the sugar molecule, and resolve it into the more stable combinations of alcohol and carbonic acid.
In order that the ferment or fungus should grow it is essential that, in addition to the cellulose and fat, it should be supplied with ammoniacal salts and soluble phosphates. These are generally present in the liquid about to be fermented; but when yeast is added to pure sugar and water “it lives at the expense of the sugar, and of the nitrogenous and mineral substances contained within itself.”[297]
[297] Pasteur.