ALCOHOLIC FERMENTATION.

Progress, Volume II, Issue 4, 1 February 1907, Page 144

ALCOHOLIC FERMENTATION.

By Percy B Phipsox, F C S

\lthough from time immemorial man has evidently had a very extensive and practical knowledge ot the phenomenon of fermentation it is only cluiing comparatively recent times that we find any attempt made to give a theoretical explanation of that phenomenon Needless to say these explanations were at first as varied as they were incorrect and this can be well understood when we remember that in the days of the alchemists all chemical actions that were accompanied by effervescence were called " fermentations." Coming to a later period we find the subject receiving a considerable amount of attention from men of science, but as these theories have, in the light of our present knowledge of the subject, merely a historical interest, they may in a short article of this description be ignoied In the year 1839 Liebig propounded the theory that yeast was a lifeless albuminous body undergoing decomposition, the molecules of which are in a state of movement and have the power of imparting this disturbance of the equilibrium to the molecule of sugar, and of thus splitting the molecule up into alcohol and carbon dioxide * In spite of the fact that Schwann and Cagniard Latour, following m the steps of Leeuwenhoek, discovered by microscopical examination that yeast consisted of" cells, which under proper conditions increase and multiply and have all the characteristics of vegetable cells, Liebig's theoiy was accepted as a perfectly satisfactory explanation, and had firm hold for thirty years or so , when this hypothesis was shattered by the publication of the results of Pasteur's epoch-making researches on this subject, which proved incontestably that fermentation was connected with the vital action oi the yeast, and although these conclusions had been arrived at by Schwann in 1836-7, it remained for Pasteur by means of extensive research to prove that Schwann's views were correct Pasteur's theory as given in his publication " Etudes sur la Biere," is as follows " Fermenta tion by yeast, that is, by the type of ferments so called, is presented to us as the direct consequence of the process of nutrition, assimilation and life when these are carried on without the agency of free o\y°ni " Fermentation by means of yeast appears, therefore to be essentially connected with the proper^ possessed by the minute cellular plant of performing its respiratory functions somewhow or other with oxygen existing combined in the sugar." In short, Pasteur's theory was that m the absence of free oxygen yeast had the power of taking the required oxygen from the sugar molecule and therefore, to further quote from his book " fermentation is life without air " Pasteur maintained that yeast will only ferment in the absence of free oxygen and that if there is present sufficient free oxygen for the requirements of the yeast cell it ceases to be a ferment To better appreciate the differences that existed between the opinion of Liebig and Pasteur on the subject it will perhaps be as well to leave the theoretical side of the subject for a few minutes and study the structure of the individual yeast cells themselves In bulk the appearance of yeast is familiar to most, but, if instead of viewing it with the naked eye we make a microscopical examination of it using a strong power of say 500 or 600 diameters, we shall rind that instead of appearing as a homogeneous pasty mass, it is consisted of innumerable cells either singly or in groups The cells consist of protoplasm enclosed by a membrane called the cell wall , this cell wall has considerable resisting power, but may be burst by pressing on the cover glass, when it will appeal as a thin transparent membrane It will also be noticed that some poitions oi the protoplasm are clearer than others These clear portions consist of cell sap and aie called vacuolcs, each cell usually showing one or two of them The cell wall is continuous, that is to sa> theie is no opening for the introduction of food, consequently all food must be conveyed into the interior through the cell wall by means of diffusion or osmosis, therefore no food can be assimilated by the yeast unless it is in solution and is also d iff usable Now, all animals and plants for their nutriment require certain complex nitrogenous bodies known

* Besides alcohol and carbon dioxide, a considerable number of by-products are formed, the most important of which are glyceime and succinic acid , so far little is known as to how the\ are formed

as piotems, with this difference that whereas animals require protein bodies ready formed, that is to sa> they are unable to form protein, which is an organic compound, out of mineral, the leverse is the case with plants This law establishes a iund-imental difference between the two In the case of yeast Pasteur found that while }east was capable of fermenting a solution of sugar, after a time the yeast arrived at a stage when it ceases to act as a ferment, although only a portion of the sugar has been fermented This was because sugar contains no food available for its development If on the other hind the yeast is added to a solution composed oi the following (Pasteur's Solution) — Potassic phosphate 20 parts Calcic phosphate 2 do Magnesic sulphate 2 do Ammomc tartrate 100 do Cane sugar 1500 do Watei 837() do 10,000 parts the growth and development of the \east goes on as readily as it would in a prepared malt wort This clearly proves that yeast has this power, a property common only to plants, and, m short, is a plant As to what position should be assigned to it in the \egetable world, it is now usually consuleied to belong to the fungi Meyei creating fo' it a new genus the Saccharomycetes Yeast under normal conditions reproduces itself by budding commencing in the form of a protubelance on the cell This protuberance goes on in creasing until it assumes a spherical form and finally separates fiom the mother cell Under starvation conditions yeast has the power of forming spores To return to the controversy that raged between the adheients of Pasteur and Liebig while the

views of the lattei scientist commenced to make considerable headway and gained some acceptance in Germany Liebig continued to make strenuous eftorts to overturn it and although he had eventually to acknowledge that yeast was a living organism, he considered that this m no way affected the conclusion that he had arrived at, and later on (1870) he was forced to modif\ his views to such an extent that while he would not accept the theory of Pasteur that fei mentation was essentially a vital action he renounced his theory of 1839, and attempted to explain the process on the assumption that during the lifetime of the yeast there was formed within the yeast cell an enzyme that effected the decomposition of sugar Why the yeast cell should secrete an enzyme to decompose the sugar if it was to den\e no benefit from so doing apparently Liebig did not satisfactorily explain md this was evidently meiely an attempt to wriggle out of an untenable position \\ though Pasteur proved that yeast, or, as we mi\ now call them the saccharomycetes, are living vegetable oiganisms his doctrine that " fermentation is life without air " was not so readily accepted and after a time was strongly controvei ted , but it remained for Adrian Brown CDirector of the School of Brewing at Birmingham Umveisity ) to prove by r some striking experiments that fermentation always takes place with greater rapidity in those cases where the fermenting liquid is well supplied with air These results directly contiadict Pasteur's hypothesis that the activity of yeast is greatest m the absence of air Prior to this Pasteur's theory was the usually accepted one, but m view of more lecent investigations it cannot now be accepted without modifications , nevertheless too much piaise cannot be given Pasteur for the invaluable research work he has done piovmg

not onh that fermentation was caused by a minute vegetable organism, but that no iermentation could take place without the introduction either by design or accident of the ferment (as opposed to the theory of Spontaneous Ceneration current at the time) and the importance of these results in placing the fermentation industries upon a scientific ba c ib cannot be over-estimated Although Pasteur's researches were carried out by means of cultures, it remained tor Hansen (a Danish investigator) to bring this system to a state of perfection, the difference between the two being that while the former obtained his growths from minute portions of }east, the latter evolved a process by which his cultures were obtained from a single cell with the result that he was always certain that his cultures were absolutely pure arid represented onl} one type , a fact that Pasteur could naturally never be certain of Hansen's researches showed that there existed innumerable types and sub-types of the saccharomycetes, and although Pasteur had to a certain extent proved this it remained for the later savant to satisfactorily classify them and discover means b} which these various types might be identified. Hansen further showed that while many of tne saccharomycetes were useful, others on the contran were exceedingly injurious, and he consequently adapted his process of securing cultures from a single cell, so that " single cell " yeast might be cultivated in sufficient quantities for commercial use and now many continental breweries are using this yeast with great success This method has, for reasons that need not be entered mto here not been extensively adopted in England, but this in no way detracts from the value of Hanson's \\ ork The next step in the solution of the problem was the important discovery a few years ago by Buchner who by triturating yeast with quartz

sand kieselguhr and water, and then submitting this to a pressure of 400-500 atmospheres between double filter clothes, obtained a faintly opalescent liquid which had the power of decomposing sugar into alcohol and caibon dioxide , and as this liquid contained no living yeast cells, it undoubtedly proved the existence of a soluble ferment or enzyme within the yeast cell capable of bringing about these changes Buchner has given this enzyme the name of zymase What the chemical nature of this substance is has not yet been settled, except that it is of an albuminous nature In view of this discovery we must now conclude that fermentation is caused by the presence of a minute vegetable organism (saccharomycetes), commonly known as yeast , this decomposition by the yeast cell is only a vital action so far as that the splitting up of the sugar molecule is necessary for the nutrition and development of the yeast, the actual breaking up of the sugar being brought about by an enzyme (zymase) secreted for this^ purpose by the cell itself although in what mannei the zymase brings about this change has not yet been ascertained It will perhaps be noticed that I have not mentioned the exceedingly interesting moleculo-physical theory put forward by Nageli, but as it cannot be accepted after the discovery of Buchner, I ha\ c accordingly omitted it The accompanying illustrations are taken from " The Microscope in the Brewery and Malthouse " by Matthews and Lott They show typical " fields " of Burton and London brewing yeast the latter a sample of deteriorated yeast , in this, apart from the worn appearance of the cells, a considerable number of bacteria (the various rod-like forms) can be observed