FERMENT A′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 po e 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 ma . 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 po e 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, . 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 proce of growth taking place in the yeast plant; the new cells of which, in a imilating 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 e ential 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. Speaking of the influence of oxygen on the development of yeast on alcoholic fermentation, Pasteur states that ready-formed yeast can germinate and grow in a liquid containing sugar and albuminous matters, even when oxygen is completely excluded. The quantity of yeast formed, however, in this case, is but small, and the fermentation goes on slowly; neverthele , a large quantity of sugar disappears (sixty to eighty parts to one part of yeast). If the air has acce to a large surface the fermentation goes on quickly, and a much larger quantity of yeast is formed in proportion to the quantity of sugar which disappears. In this case, also, oxygen is absorbed by the yeast, which grows quickly, but does not act so decidedly as a ferment, inasmuch as only four to ten parts of sugar disappear for one part of yeast produced. When the air is excluded the same yeast again acts as a powerful ferment. Pasteur, therefore, infers that yeast which acts as a ferment in the absence of air abstracts oxygen from the sugar, and that upon this deoxidising power its action as a ferment depends. The violent activity of the yeast at the commencement of the fermentation is due to oxygen di olved in the liquid. In liquids containing albumen (yeast and water, .) yeast likewise grows, though sparingly, even if the solution does not contain a trace of sugar, provided there is a sufficient acce of air. But if the air is excluded this does not take place, even though the liquid may contain, besides albumen, a non-fermentable sugar, such as milk sugar. The yeast formed in a liquid not containing sugar po e es all the properties of a ferment, and excites fermentation in a solution of sugar excluded from the air. [298] [298] ‘Bull. Soc. Chem.,’ 1861, pp. 61, 79. Similarly, Pasteur regards putrefaction as a kind of fermentation, set up and maintained by an animal organism, or ferment belonging to the genus Vibrio . Putrefaction, when taking place in contact with the air, is always accompanied by decay or EREMACAUSIS . The abandonment of the old theory as to the nature of eremacausis, viz. that it consisted in the gradual combustion of decaying organic matters by atmospheric oxygen, has been nece itated by the experiments of Pasteur, Schröder, and others, which have conclusively established the facts that organic substances are not oxidised by perfectly pure air, and that their decomposition and subsequent destruction are due to the presence in the air of the sporules or seeds of certain low organisms. Pasteur cites numerous instances corroborative of the statement that perfectly pure oxygen fails to affect, save to a very limited extent, organic substances. In one case an aqueous infusion of yeast mixed with sugar was enclosed in a sealed flask with double its volume of air, which had been previously depurated by being made to pa through a red-hot tube. At the end of three years the liquid (which had during part of the time been kept at a temperature of from 25° to 30° Cent.) was found to be perfectly fresh and transparent, and the air when examined gave 18·1 vols. of oxygen, 80·5 vols. of nitrogen, and 1·4 of carbonic acid. Under the same conditions urine and milk, whether fresh or previously boiled, showed minute traces only of oxidation; crystals of uric acid and phosphates formed in the urine, but the milk was unaltered, having preserved its alkaline reaction, and showed no disposition to curdle. Very different, however, was the result when either of the above substances was enclosed with ordinary air. It was then found that in a few days the whole of the oxygen was absorbed, carbonic acid being at the same time simultaneously formed. A certain quantity of moistened oak sawdust kept in contact with ordinary air for a fortnight was found at the end of that time to have absorbed 140 cubic centimètres of oxygen; whilst the same amount of sawdust enclosed with an equal volume of purified air had removed only a few cubic centimètres of the gas in a month. In the former experiment a microscopic film of mycelia and spores of Mucidineæ formed on the sawdust. From numerous experiments of a like nature with the above, and attended with analogous results, chemists and physiologists now generally regard eremacausis as effected by agencies similar in character to those which produce fermentation and putrefaction. “The observations of Schröder upon the proce es of fermentation and putrefaction are remarkable. He has shown that any organic liquid may be prevented from fermenting or putrefying if it be heated under pre ure to about 266° F. (130° C.), then transferred to a flask and boiled, the mouth of the flask being plugged whilst boiling with a pellet of cotton wool, which is left in the neck of the flask. In this way he preserved, during a hot summer, various liquids, including freshly-boiled wort, blood, white of egg, whey, urine, broth, and milk; but when afterwards the plug of cotton wool was withdrawn these liquids in a few days began to undergo decomposition. He explains these results by supposing that the spores of some organism must find acce to the substance in order to set up the proce of decomposition. By a temperature of 260° F. (126·7° C.) any such spores which the substance itself might contain are destroyed, and as the air is filtered through the cotton wool before it reaches the interior of the flask, none of these organic germs can afterwards gain acce to the body under experiment. I have repeated some of these experiments with complete succe . [299] [299] The Editor of this work has also repeated Schröder’s experiments on milk, and obtained the same results. “If air be transmitted with suitable precautions slowly through narrow ignited platinum tubes, so as to destroy all suspended organic particles, no fermentation or putrefaction will take place on admitting such air into contact with putrescible substances previously heated to 260° for an hour.” [300] [300] Miller. Pasteur has shown the existence of these floating germs in the air by drawing a large volume of atmospheric air, by means of an aspirator, through a narrow tube obstructed by collodion wool. On subsequently di olving this wool in a mixture of alcohol and ether various microscopic sporules were left undi olved. The entire absence of the exciting causes—warmth, air, and moisture—leaves even those substances which under ordinary circumstances are most liable to change, in a state in which they may remain for an almost indefinite period without perceptible alteration. Thus, animal substances in a frozen or dry state do not undergo decomposition, nor does a solution of sugar or the juice of grapes (must) when perfectly excluded from the air; but on the mere exposure of these substances to warmth, moisture, or atmospheric air, putrefaction or fermentation immediately commences. Remove the cork from the bottle of ‘capillaire’ on the parlour sideboard, or pierce the skin of one of the grapes on the de ert table with a needle, and these bodies, which would have otherwise suffered no change for weeks, or even months, will soon exhibit symptoms of spontaneous decomposition. The knowledge of this fact has been practically applied to the preservation of animal and vegetable substances for food. Even the most putrescible of these may be preserved for an unlimited period by enclosure in metallic cases, or gla bottles, from which the air has been completely removed and excluded. The important duties which fermentation or putrefaction performs in the economy of our globe, and in several of the arts of life and civilisation, have long rendered the development of its principles an object of the highest interest and importance, both in a scientific and practical point of view. In its most extended sense, this subtile proce of nature, though occasionally productive of injurious effects, may be regarded as one of the most nece ary and beneficial with which we are acquainted. Like the labours of a scavenger, it speedily removes from the surface of our globe those matters which would otherwise remain for some time without undergoing decomposition. It either di ipates in air, or reduces to more fixed and useful forms of matter, those organic substances which, by their presence, would prove noxious, or, at all events, usele to the animal and vegetable kingdoms. It is the giant power that cleans the Augean stable of nature, at the same time that it provides some of the most esteemed articles of utility and luxury for the well-being and enjoyment of man. Chemists have distinguished fermentation into different varieties, which, in general, are named after the more important products of its action. Of late years, the number of these varieties has been greatly increased by the extension of the term to several operations besides those formerly included under it. See Acetification , Bread , Putrefaction , Brewing , .