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OBSERVATIONS on the phenomena of fermentation are of great antiquity, and were first made by those who prepared the juices of sugary plants, e.g., that of the grape. The agitation which the entire mass undergoes, and the continued production of gaseous bubbles which break on the surface, must have recalled to them the ebullition of liquids exposed to heat. It is to this striking analogy to the process of boiling that the word “fermentation its derivation (fervere = to boil). The worship of Bacchus testifies to the fact that the ancients were acquainted with the properties of wine, and there is ample evidence to conclude that alcoholic fermentation was empirically known in the prehistoric epoch.
In the writings of alchemists in the Middle Ages the word “fermentation" is frequently used; but its application was too vague and comprehensive. Being unacquainted with elementary chemistry, every chemical action was to them a sort of fermentation. Some were, no doubt, struck with the fact that a small amount of leaven transforms into fresh leaven an enormous quantity of dough. The knowledge of this property of the transmission of a force to a large mass, without the original force being itself weakened in the process, naturally led them to seek for the “ philosopher's stone”.
Nothing of any consequence, however, was accomplished
till the end of the eighteenth century, when chemistry made a great stride under the genius of Lavoisier. Starting with the principle of the indestructibility of matter, he endeavoured to ascertain the chemical process involved in alcoholic fermentation.
In 1837 Schwann discovered the remarkable fact that fermentation is not a mere chemical molecular transformation, but a physiological process of the living yeast cells. The dependence of fermentation on living yeasts is shown by the facts that living cells are present in all fermenting fluids, and that fermentable substances do not ferment when the entrance of living yeast cells is prevented by heat or filtration through cotton wool, And further, the intensity of fermentation runs parallel with the development of the organisms in the fermenting fluid.
Liebig considered all fermentations as molecular movements, which a body in a state of chemical movement, i.e., decomposition, transmits to other substances whose elements are not very firmly combined. He denied the all-important role of living organisms.
Pasteur overthrew this theory by a series of ingenious researches, and thereby laid the foundation of fermentation physiology. He, however, thought that fermentation was “ life without air”. But this is incorrect, as many fermentations occur in abundance of oxygen.
Admitting, then, that living cells are the cause of fermentation, let us proceed to inquire as to how this action is brought about.
According to one explanation, fermentation is due to the action of certain ferments or enzymes, which the organisms secrete, in common with other animal and vegetable cells. Buchner, by subjecting yeast cells to high pressure, has obtained a liquid substance which, without the intervention of living cells, is capable of
inducing alcoholic fermentation. But it is not certain that this pressure-extract is really an enzyme. Macfadyen, in repeating Buchner's experiment, found that the substance of crushed yeasts, of itself, contains alcohol, which shows that the actual fermentative changes take place in the interior of the cells. Besides, the numerous byproducts formed in the fermentation process cannot be due to the action of enzymes, but rather to the metabolic activity of the cell-protoplasm.
The ammoniacal fermentation of urea, however, is undoubtedly due to an enzyme, which has recently been isolated from its organism—the micrococcus urea.
But in this case, the process is one of simple hydrolysis, and no by-products are formed.
It is not suggested that enzymes do not play an important part in all fermentative processes. But their function is largely limited to the preparatory changes which they induce in the nutrient medium, rendering it more assimilable by the living protoplasm. Thus, the inversion of sugars and peptonisation of albumens is the result of the enzymes secreted by the organisms. But the actual fermentative changes are brought about in the protoplasm itself, and are the direct result of its metabolic activity.
We see, then, that the process of fermentation is intimately connected with the presence of the living organisms which consume the elements necessary for their growth, and cast off the residue as excretory products. The result is the degradation of the complex organic compounds and their rearrangement into simpler ones.
All organisms capable of exciting fermentation possess certain characteristics in common. Pasteur long ago ascertained that all organised ferments are :
(1) Nitrogenous organic bodies.
(2) They are unstable.
(3) A relatively small quantity can produce great changes in the substance acted upon, especially if the metabolic products are removed as quickly as they are formed.
To these points must be added the specificity of ferments, that is to say, each ferment produces its particular fermentation and no other. Thus if we introduce simultaneously in the same saccharine medium, alcoholic, lactic, and butyric ferments, we see three distinct reactions side by side-one breaks up the sugar into alcohol and Co, ; the second converts it into lactic acid; and the third into butyric acid.
Apart from the nature of the organism, the products of fermentation will vary with the nature of the fermented body. Heat and moisture are necessary conditions for the fermentation process, but neither of them can give rise to it.
The process of fermentation is so important both from a scientific and a commercial standpoint that it is desirable to give some instances of its applications in industrial processes. It will be seen how numerous are the products formed by bacterial agency, and how largely mankind is indebted to such organisms.
Alcoholic Fermentation.—When grapes are crushed the grape sugar is fermented — alcohol and CO, being formed.
To what is this change due?
It is caused by a torula or yeast naturally present on the skin of the grapes.
The latter when crushed permit the organisms to operate on the juice, which disappears, or rather reappears as alcohol.
C.H208 = 2C,H,0 + 2CO.,.
Yeast cells are the most ubiquitous of all fungi. They are round or oval in form, and are made up of granular
protoplasm, surrounded by a definite Groups of Mother capsule. They reproduce by “budbud
cell Fig. 1.--Yeast Cells.
ding”. [From Schenk's When yeast cells are grown on
Bacteriology.] an unfavourable medium, as gypsum block, they form spores within their capsule. This fact was taken advantage of by Hansen for the identification