On Fermentation

On Fermentation

THE INTERNATIONAL SCIENTIFIC SERIES, ON FERMENTATION BY P. SCHUTZENBERGER UGRECTOR AT THE CHEMICAL LABORATORY AT THE: SORBONNG WITH TWENTY-EIGHT ILLUSTRATIONS NEW YORK D. APPLETON AND COMPANY 1893 CONTENTS. PAGE INTRODUCTION . ° ° . e e . ° . I BOOK I. FERMENTATION DUE TO CELLULAR ORGANISMS, OR DIRECT FERMENTATION. CHAPTER I, HISTORICAL « 6 - + + «© © © © «© 9 CHAPTER II. ALCOHOLIC OR SPIRITUOUS FERMENTATION . e . 418 CHAPTER III. ALCOHOLIC FERMENTS . . . . e e . - 34 . CHAPTER IV. ACTUAL COMPOSITION OF FERMENTS . . ° . e 63 CHAPTER V. FUNCTIONS OF YEAST . . : . ° . oe 72 CHAPTER VI. ACTION OF VARIOUS CHEMICAL AND PHYSICAL AGENTS ON ALCOHOLIC FERMENTATION . . . ° . 159 CHAPTER VII. CAN NOTHING BUT ALCOHOLIC YEAST EXCITE ALCOHOLIC FERMENTATION? . 2. «© «© «© © © « 16 7 ¢#28R v1 CONTENTS. CHAPTER VIII. VISCOUS OR MANNITIC FERMENTATION OF SUGAR . CHAPTER IX. LacTIC FERMENTATION se 8 lel CHAPTER X. AMMONIACAL FERMENTATION . . «6 ¢ CHAPTER XI. BUTYRIC FERMENTATION AND PUTREFACTION . e CHAPTER XII. FERMENTATION BY OXIDATION . .« © © e CHAPTER XIII. APPLICATION OF THE RESEARCHES AND IDEAS OF PASTEUR. . «© «© © © «© © BOOK II. PAGE 189 193 203 228 245 ALBUMINOID SUBSTANCES—SOLUBLE OR INDIRECT FERMENTS— ORIGIN OF FERMENTS. CHAPTER I. ALBUMINOID SUBSTANCES, OR PROTEIDS . «. CHAPTER IIL SOLUBLE FERMENTS, AND INDIRECT FERMENTATION CHAPTER III. ON THE ORIGIN OF FERMENTS . »- 2 «© LIST OF ILLUSTRATIONS. Fig. 1.—Saccharomyces cerevisiae — Sedimentary yeast, X 400 diams. . . . . . . . Fig. 2,—Saccharomyces cerevisise—Sedimentary yeast, bud- ding, X 400 diams. . * 6 Fig. 5S aenaromyees cerevisiae Surface yeast, budding, x 400 diams. . . . . . . . Fig. 4.—Saccharomyces cerevisie—Surface yeast, at rest, X 400 diams. . . ary . , Fig. 5.—Saccharomyces cerevisiee Sedimentary yeast, in a growing state, x 400 diams. . . . . Fig. 6.—Saccharomyces cerevisise— Formation of spores, x 750 diams. a, 4, c, d, e, successive phases of the production of spores. . «. «|. . Fig. 7.—Triads of spores, germinating, x 750 diams. . Fig. 8.—Saccharomyces ellipsoideus, in process of Pudding, x 600 diams. . . . Fig. 9.—Saccharomyces ellipsoideus, derelopment of spores, X 400 diams. . . Fig. 10.--Saccharomyces ellipsoideus, group of spores i in the act of germinating, x 400 diams. . + Fig. 11.—Saccharomyces Pastorianus, X 400 diams. . Fig. 12.—Saccharomyces exiguus, X 350diams. . . . Fig. 13.—Saccharomyces conglomeratus, x 600 diams.. . race 45 47 47 49 49 51 51 55 55 56 56 56 viii LIST OF ILLUSTRATIONS, Fig. 14.—Saccharomyces apiculatus (Rees). Carpozyma apic. (Engel), apiculated ferment, x 600 diams. Fig. 15—Saccharomyces Reesii, ferment of red wine, x 350 diams.. . . « «© © «© « Fig. 16.—Saccharomyces mycoderma, x 350diams. . . Fig. 17.—Saccharemyces mycoderma . . - 6 Fig. 18.—Mucor racemosus, ferment in mass . . Fig. 19.—Apparatus for the measurement of oxygen dis- solved in water . * 8 © «© - . Fig. 20.—Viscous Fermentsof Wine . 2. «© «© . Fig. 21—Lactic Ferment . . 2. .« «6 «© « Fig. 22—Mycodermaaceti . . .« «6 «© «© © Fig. 23.—Giret and Vinas’ apparatus for warming wines. Figs. 24 and 25.—Organic corpuscules of dust, mixed with amorphous particles . . . . . Fig. 26.—M. Pasteur’s apparatus for the introduction of cal- cined air into flasks containing organic infusions Fig. 47.—M. Pasteur’s apparatus for studying the resistance of germs and spores to temperatures more or less elevated . . . . . . . . Fig. 28.—M. Pasteur’s flask to deprive the air of its germs . NOTE BY TRANSLATOR. The French words “‘invertir,” ‘‘inverti,” ‘‘intervertir,” ‘‘ inversive,” PAGE 57 59 59 59 60 121 190 198 239 247 317 319 323 323 &e., p. 28, &c., may be rendered in English by the recognized terms, ‘‘ inverted,” ‘‘inversive,” &c, Yet since these terms are not understood by all, and present some difficulty, it has been thought better to adopt in the text the less technical and more suggestive rendering ‘‘ altered,” ‘‘ alterative, ' &c.; by altered sugar being meant cane-sugar which has taken up a molecule cf water and split up into a mixture of glucose and levulose. ON FERMENTATION. INTRODUCTION. FERMENTATION is only a particular instance, selected from among the chemical phenomena of which living organisms are the field ; it, like all biological reactions, comes before us as a manifestation of the special force residing in these organisms, or rather in their cellular elements. If we leave the nature of the fermenting body, and the products derived from it, in the background, there is nothing to distinguish fermentation from the other chemical transformations which take place in the animal or vegetable economy. The reason why the production of alcohol and carbon dioxide at the expense of sugar, the conversion of glucose into lactic and butyric acids, and other pheno- mena of the same order have been classed by them- selves, is that the real cause of these curious transfor- mations was long misunderstood. It had not been observed that they had as their origin the presence of living organisms, or, at Icast, principles which are directly derived therefrom. 2 ON FERMENTATION. There is, therefore, no longer any necessity, in the present state of science, for grouping together under a special name these various reactions ; it is more con- venient, on the contrary, to class them among the general mass of chemical phenomena of the living organism, We must, consequently, do one of two things; either cease to use the term fermentation, as a general ex- pression applying to a certain order of phenomena, or we must designate by it all those changes which, by the special conditions under which they are pro- duced, are evidently due to the intervention of a force differing from those which we handle in our labo- ratories. It is true that the organisms which give rise to what have been hitherto called fermentation are simple ‘elementary organisms reduced to a single cell; but a plant or an animal of a high order is only the union, under special laws, of different kinds of cells, each of which acts in a certain determinable manner. When, as M. Pasteur has remarked, we sow at the same time, in the same saccharine medium, alcoholic, lactic, and butyric ferment, we see three distinct reactions take place, one of which splits up the sugar into alcohol and carbon dioxide, the second converts it into lactic acid, and the third into butyric acid. The more simple an organism is, the fewer special kinds of cells it contains, the simpler are the chemical reactions which take place in it, and the more easily are they separated from each other, and isolated by experi- ment. On the contrary, in proportion as the histological constitution is varied and heterogeneous, we see a Digitized by G O08 le INTRODUCTION. 3 greater number of distinct compounds, as the products of the many chemical changes which take place in the different tissues. As a consequence of what we have just said, our plan would be considerably enlarged, and the history of fermentation would become that of the chemical phe- nomena of life. _ We will not, however, give such a wide scope to this work, but will confine ourselves to the examination of the phenomena which have been hitherto designated by the name of fermentation. Under these restrictions, the history of fermentation may be considered as an intro- duction to biological chemistry. In fact, it is easily seen, from the preceding consi- derations, that the thorough study of ferments, properly so called, or rather of elementary organisms, and of their mode of existence, ought to precede that of the more complete beings. We more easily understand the properties of granite, and the influence exerted upon it by water and atmospheric agents, when we have learned that it is formed of crystals of quartz, felspar, and mica in juxtaposition, and have studied the chemical characters of each of these compounds. In the same manner, the study of the chemical manifestations of the vital force in cellular organisms is destined to throw a bright light on the more complex functions of the higher plants and animals. This has been recognized by M. Pasteur, and by all those who have subsequently entered on the physiological study of fermentation, and of the develop- ment of cellular organisms. A living cell of beer-yeast possesses the property of resolving into alcohol, glycerin, carbon dioxide, and 4 ON FERMENTATION. succinic acid the altered sugar which penetrates by endosmose through its membranous envelope. If we substitute for the cell of beer-yeast a cell of lactic ferment, we still see the sugar disappear, but the products into which the ponderable elements of the glucose are resolved are different; instead of alcohol and carbon dioxide, we have iactic acid. The modus faciendi of the vital force of this cell is evidently not the same as that of the former one; but we cannot, therefore, affirm that there are as many vital chemical forces as there are reactions. When a pencil of solar light passes through a prism, the constituent parts of this pencil are isolated on account of their unequal refrangibility. The least refrangible rays are revealed to us by the effects of heat (the dilatation and change of condition of bodies) ; next come the luminous rays, which excite on the retina the impressions of colour forming the spectrum ; and then, beyond the violet, is a series of invisible rays, which are revealed only by their decomposing action on certain combinations (salts of silver, &c.). But we know now that all these calorific, luminous, and chemi- cal rays, some of which give heat without light, and others light without heat, or excite chemical reactions, differ only in the rapidity of the vibratory movements of the ether, and are essentially distinguishable from each other only by their wave-length. It is possible that an analogous bond may unite the vital chemical forces of the different elementary organisms. Sand, sprinkled uniformly on the surface of a vibrating plate, collects in nodal lines of different forms, according to the sharp- ness of the note which we draw from this plate by Digitized by G O08 le INTRODUCTION. 5 means of a bow; in the same manner, chemical com- pounds may perhaps be resolved into more simple combinations, varying in kind according to the vibratory rhythm which starts them. The transformation of sugar into alcohol and carbon dioxide, and the conversion of the same body into lactic acid are chemical phenomena which we cannot yet reproduce by the intervention of heat alone, nor by the additional agency of light or of electricity. The force capable of attacking, in a certain determinate direction, the complex edifice which we call sugar, an edifice composed of atoms of carbon, hydrogen, and oxygen, grouped according to a determinate law—this force, which is manifested only in the living cell of the fer- ment, is a force as material as all those which we are accustomed to utilize. Its principal peculiarity is, that it is only found in the living organisms, to which it gives their peculiar charac- ter. We ought not to allow ourselves to be stopped by this rampart, over which no one has hitherto been able to pass; we ought not to say to the chemist, “ You shall go no farther, for beyond this is the domain of life, where you have no control.” The history of science shows us the weakness of these so-called impassable barriers. Gerhardt, when he published his excellent treatise on organic chemistry, thought himself justified in say- ing, “It is vital force alone which acts synthetically and reconstructs the edifice demolished by chemical forces.” M. Berthelot, some years afterwards, in a brilliant series of discoveries, made the first successful attempt to 6 ON FERMENTATION. perform organic syntheses, and determined the principal conditions under which they can be effected. In a remarkable lecture on molecular dissymmetry (Lecgons de la Société Chimique de Paris, 1860), M, Pasteur had established an important distinction between artificial organic products and the compounds formed under the influence of living organisms. “ The artificial products of the laboratory have coinci- dent images (sont 4 image superposable). On the con- trary, most of the natural organic products—I might say all, if I had only to allude to those which play an impor- tant part in the phenomena of vegetable and animal life— all the products essential to life are unsymmetrical, and unsymmetrical in such a way that their images cannot be made to coincide with them.” And afterwards he says, “ We have not yet been able to realize the produc- tion of an unsymmetrical body, by the aid of compounds which are not so themselves.” Nearly at the same time that these words were uttered before the Chemical Society of Paris, two English chemists, Perkin and Duppa, succeeded in transforming succinic acid into tartaric acid. M. Pasteur himself acknowledged that the artificial pro- duct of Perkin was a mixture of paratartaric acid and of inactive tartaric acid. But paratartaric acid easily splits up, as Pasteur’s elegant experiments have shown, into dextro-tartaric and lzvo-tartaric acid, and M. Jungfleisch has shown that inactive tartaric acid, heated with water at 175°, is partially converted into para- tartaric acid. The succinic acid employed by the English chemists was formed by the oxidation of yellow amber. This Digitized by G O08 le INTRODUCTION. vi was not a synthetical product; it might be thought that, though it was inactive, it resulted, like racemic acid, from the union of two active but opposed mole- cules. Jungfleisch has removed this last doubt. He prepared synthetic succinic acid by a well-known method, by means of cyanide of ethylene and potassium. This acid furnished paratartaric acid, like that produced from amber. Thus fell the barrier placed by M. Pasteur between natural and artificial products. This example shows us how cautious we ought to be in making distinctions which we seem justified in establishing between the chemical reactions of the living organism and those of the laboratory. Because a chemical phenomenon may hitherto have been produced only under the influence of life, it does not follow that it will never be effected otherwise. No one can any longer admit that vital force has power over matter, to change, counterbalance, or annul the natural play of chemical affinities. That which we have agreed to call chemical affinity is not an absolute ~ force; this affinity is modified in numberless ways, according as the circumstances by which bodies are surrounded, vary. Thus, the apparent differences between the reactions of the laboratory and those of the organism ought to be sought for, more particularly among the special conditions, which the latter alone has been able hitherto to bring together. In other words, there is really no chemical vital force. If living cells produce reactions which seem peculiar to themselves, it is because they realize conditions of molecular mechanism which we have not hitherto suc- 8 ON FERMENTATION. ceeded in tracing, but which we shall, without doubt, be able to discover at some future time. Science can gain nothing by being limited in the possibility of the aims which she proposes to herself, or the end which she seeks. , If, in this work, we still employ the expression, “the vital chemical force of an elementary organism,” it will be clearly understood that we intend these words to signify the realization of the conditions of molecular mechanism necessary in order to set up a certain reaction. We will not delay any longer over these general considerations, which are, after all, nothing but hypo- theses, naturally suggesting themselves to the mind of him who seeks to explain the causes which produce certain observed effects, but on which it is not neces- sary to dwell at the present stage of our inquiry; we will therefore proceed at once to the examination of facts. The study of fermentation may be divided into two parts, according to the nature of the ferment. The first will comprise the fermentation due to the inter- vention of an organized ferment, having a determinate form; the second will be reserved for fermentation produced by soluble products, elaborated by living organisms, BOOK I. FERMENTATION DUE TO CELLULAR ORGANISMS, OR DIRECT FERMENTATION, CHAPTER I. HISTORICAL, THE word fermentation is derived from fervere, to boil; it evidently owes its origin to the reaction presented by saccharine liquids, when they are left to themselves or placed in contact with ferments. We observe, in fact, in this case, a more or less abundant disengagement of gas, which causes the liquid to effervesce or boil. The sugar disappears, and the product becomes spirituous. The expression, fermentation, was subsequently applied to other phenomena, in which an organic body, when dissolved, is modified, changed, and transformed, under the influence of a cause which remained for a long time unknown and badly defined. Thus the acidification of wine was called fermentation, although in this case there was no effervescence. The analogy of the deter- mining cause was considered, rather than the appear- ance of the phenomenon. Alcoholic fermentation was the first known, and was 1o . ON FERMENTATION, also more studied than the other reactions of this class. Osiris among the Egyptians, Bacchus among the Greeks, Noah, according to the Israelitish tradition, taught men the art of cultivating the vine, and making wine. Moses, in his writings, draws a distinction be- tween unleavened and leavened bread, and relates that the Israelites were in such haste, during their flight from Egypt, that they had no time to put leaven into their dough. The ancients used as leaven for their bread either dough that had been kept till it was sour, or beer- yeast. “Gallie et Hispania frumento in potum resoluto, spuma ita concreté pro fermento utuntur, qua de causa levior illis, quam ceteris, panis est,” says Pliny, who also adds, that in the fermentation of bread acidity is the most active principle. From the earliest times cer- tain fermented liquids were known, both in Egypt and Germany, prepared from natural saccharine juices which had been allowed to ferment; such as beer, hydromel, palm-wine, and cider. We find, in short, from all ancient documents, that alcoholic fermentation was empirically known in its principal effects, and utilized at a period far earlier than that which has left written traces of its history. Among the writings of the alchemists from the thirteenth to the fifteenth century, we very frequently find the expressions “fermentation and ferments ” (fermentatos et fermentum), without our being able to ascertain clearly what precise ideas they attached to them. They knew no distinction between mineral and organic substances; the phenomena connected with the changes in organic products were assimilated and Digitized by G O08 le HISTORICAL, It confounded with the transformations of mineral com- pounds, and with the solution of salts and metals. The term “ferment” was often applied even to the philo- sopher’s stone. “ Apud philosophos fermentum dupliciteo videtur dici; uno modo ipse lapis philosophorum -et suis elementis compositus, et completus in comparatione ad metalla; alio modo illud, quod est perficiens lapidem et ipsum complens. “De primo modo dicimus, quod sicut fermentum paste vincit pastam, et ad se convertit semper, sic et lapis convertit ad se metalla reliqua. Et sicut una pars fermenti paste habet convertere partes paste et non converti, sic et hic lapis habet convertere plurimas partes metallorum ad se, et non converti."—-PETRUS Bonus of Ferrara, 1330-1340. . We see that the writer is especially struck with this fact, that a very small quantity of leaven transforms into fresh leaven an almost indefinite quantity of paste. This property of transmitting a force to a large mass without being itself weakened by the process, was pre- cisely that which ought to characterize the philosopher's stone which was so much sought after. Basil Valentine, in his “Triumphal Car of Antimony,” admits that yeast, employed in the preparation of beer, communicates to the liquor an internal inflammation, and determines thereby a purification, and a separation of the clear parts from those which are troubled. Alcohol, the presence of which in the fermented liquid was known to him, was considered by him to exist previously in the decoction of germinated barley ; but that it did not become active and susceptible of war 12 ON FERMENTATION, being separated by distillation until it had been cleared from the impurities which accompany it, and mask its special properties. Libavius (Alchymia, 1595) believed that, “ Fermen- tatio est rei in substantia, per admistionem fermente quod virtute per spiritum distributo totam penetrat massam et in suam naturam immutat, exaltatis.” The ferment must be of a similar nature to the matter which enters into fermentation, and the latter must be either liquid, or in a state of minute division; the principal agent resides in the heat of the ferment. Like the chemists of a later age, Libavius compares fermentation to putrefaction, and considers them as dif- ferent effects of the same cause. He protests,-on the contrary, against the confused ideas which had been entertained concerning digestion and fermentation. Digestion is, according to him, “motus ad mistionem, non ad perfectionem,” as fermentation is. The iatro-chemical school attributed to fermentation a preponderating power, and even confounded under this term a great number of chemical reactions, Thus Van Helmont expresses himself as follows in his “Ortus Medicine” (648): “Docebo omnem trans- mutationem formalem presupponere fermentum cor- ruptivum.,” The formation of intestinal gasses, the production of blood and animal fluids, spontaneous generation, the effervescence of chalk under the influence of acids, are phenomena with which fermentation has to do. We may, however, say in passing that Van Helmont had the merit of clearly distinguishing the production of a special gas (gas vinorum) during alcoholic fermen- Digitized by G O08 le HISTORICAL. 13 tation. He says that this gas vinorum is different from spirit of wine, as he was able to prove by experiments, It is impossible to discover from his writings whether or no he recognized the identity of the gas vinorum and the gas carbonum produced during the combustion of charcoal. In 1664, Wren pointed out that the gas produced by alcoholic fermentation can be absorbed by water, like that which is disengaged by the action of an acid on salt of tartar. Silvius de la Boé (1659) no longer regarded the effer- vescence of the alkaline carbonates under the influence of acids as a phenomenon of the same class as fermen- tation. He supposed that in the former case there was com- bination, in the latter decomposition. Lemery (Cours de Chimie, 1675) is not so explicit when he says: “The fermentation which occurs in paste, wort, and all other similar things, is different from that of which we have just spoken (effervescence), since it is slower ; it is excited by the natural acid salt of these substances, which, becoming disengaged, and having its energy increased by its motion, rarefies and raises the gross and oily part which opposes its passage, and thus we see the matter rise. “The reason why the acid does not cause sulphurous substances to ferment with as much noise and readiness as alkalis, is that oils are composed of pliant parts which yield to the points of the acid, as a piece of wool or cotton would yield to needles pressed into it. Thus it seems to me that we must admit of two sorts of fermentations ; one of acids with alkalis, which would be called effer- 2 a 14 ON FERMENTATION. vescence ; and the other would be, when the acid rarefies by degrees a solid matter like paste, or clear and sulphurous like wort, cider, or other juices of plants; we should call the latter sort fermentation.” : Lemery says again, when speaking of alcoholic fermem= tation: “In order to understand this effect, we must know that wort contains much essential salt ; this salt, being volatile, makes an effort, during fermentation, to defach itself from the oily particles by which it is, as it were, bound ; it penetrates them, divides and separates them, until by its subtile and piercing points, it has rare- fied them into spirit; this effort causes the ebullition which takes place in wine, and, at the same time, its purification; for it separates and removes the grosser parts in the form of froth, a portion of which attaches itself to the sides of the vessel and grows hard; the other falls to the bottom, and is called tartar and lees. The inflammable spirit of wine is therefore nothing but an oil exalted, that is purified, by salt.” We find in the researches and writings of Becker (1682), a very marked progress in the study of the pro- ducts of fermentation. He was the first to bring for- ward the important fact that saccharine liquids alone are capable of entering into spirituous fermentation, He considers that alcohol does not pre-exist in the wort, but is formed during the process of fermentation ; the intervention of air is necessary to set this action going, which he considers analogous to combustion, Becker brings together, under the name of fermentation, the production of gas in the stomach of sick animals (insumefactio), spirituous fermentation (proprie fermen- tatio), and acetification (acetificatio seu acescentia). Digitized by G O08 le HISTORICAL, ly We owe to Willis (1659), and to Stahl, the celebrated originator of the theory of phlogiston (1697), the first philosophical conception of the peculiar nature of fer- mentation, or rather of fermentations. According to their views a ferment is a body endued with a motion peculiar to itself, and it transmits this motion to the fermentable matter. Thus Willis says in his disserta- tion “ De Fermentatione”:— . . “Fermentatio est motus intestinus cujusvis corporis, cum tendentia ad perfectionem ejusdem corporis vel propter mutationem in aliud. Plures sunt modi quibus fermentatio promooctur. Primus et principius erit fermenti cujusdam corpori fermentando adjectio; cujus particule cum prius sint in vigore et motu posite, alias in massa fermentanda otiosas et torpidas exsuscitant, et in motum vindicant.” Stahl considered alcoholic fermentation as a pheno- menon of the same class as putrefaction, and as only a particular case of it. As there was at that time no definite idea of the elementary composition of ferment- able substances, and of the products of their fermenta- tion, there evidently could not be established any correct relation between these bodies, and any hypothesis could be safely brought forward. Thus Stahl considers that fermentable matter (sugar, flour, milk) is composed of particles formed by the unstable union of salt, oil, and earth ; under the influence of the internal motion excited by the ferment, the heterogeneous particles are separ- ated from each other, and then recombined so as to form more stable compounds including the same prin- ciples, but in other proportions. From Stahl to Lavoisier we find no names of great 16 ON FERMENTATION. note, and no interesting discoveries with respect te fermentation. When chemistry underwent its great transformation at the end of the last century, under the powerful influ- ence of the genius of Lavoisier, fermentation necessa- rily attracted anew the attention of experimentalists. Lavoisier himself studied it (Elemens de Chimie, vol. i. p- 139, second edition), and as was the case with all subjects which he handled, he threw a ray of light upon the darkness. Proceeding in his usual manner, balance in hand, by weight and measure, and applying to the solution of the problem the new methods of organic analysis which he had invented, he endeavoured to ascertain the bond or relation which exists between the fermented matter, the sugar, and the products of fermentation, alcohol and carbon dioxide. From this moment we quit the domain of the history of the science, and enter into that of the real and well- observed facts which will be treated of in the following chapters. We may say, in recapitulation, that, before thé labours of Lavoisier and his followers, the fermentable products and the principal terms of their transformations (carbon dioxide gas, alcohol, acetic acid, &c.) were known gua/i- tatively. The distinction between the acid, or acetic fermentation, and the alcoholic fermentation was known; there was an idea of the analogy which exists between putrefaction and alcoholic fermentation; and an ex- planation of the manner in which a ferment acts had been sought. The latter was known only as a kind of foam, deposit, or paste, in which resjded an occult and special force, Digitized by G O08 le HISTORICAL, 17 capable of determining chemical phenomena. We may add that these phenomena were considered as distinct, both in their action and exciting cause, from the ordinary reactions of chemistry. This was, as one may see, but a slight result of the many volumes that had been written on this subject. Spirituous or alcoholic fermentation being, in every respect, the part of this subject which has been the most thoroughly studied, we will commence our monograph by its examination. 13 ON FERMENTATION. CHAPTER IL. ALCOHOLIC OR SPIRITUOUS FERMENTATION. PASTEUR, in his excellent memoir (Ann. de Chimie et Physique, 3rd series, vol. lviii. p. 323), calls by the name of alchoholic fermentation that which sugar undergoes under the influence of the ferment which bears the name of yeast or barm, We can only adopt this definition as applying, with- out any possibility of uncertainty, to a phenomenon very limited in its cause and its effects; but we shall have to inquire, in a later portion of this work, whether alcohol cannot be produced at the expense of sugar under other influences than those of the product known as beer-yeast. As we have before said, the splitting up of a molecule of sugar into many more simple products, among which we find alcohol and carbon dioxide, is the consequence of a special mechanical action, exercised on the ultimate particles of the compound matter. Whatever may be the source, whether living organism or dead matter, which realizes the conditions necessary for this rupture of equilibrium, the phenomenon will be essentially the same. In a general and philosophical point of view, there is no more reason why we should separate alco- holic fermentation excited by yeast from that which is due to any other agent, than why we should Digitized by G O08 le . ALCOHOLIC OR SPIRITUOUS FERMENTATION. 19 distinguish cane sugar from that produced from beet- root. While we restrict, with Pasteur, the expression “alco- holic fermentation,” and do not include in it all the phenomena of decomposition, in which alcohol is pro- duced, we have to consider the body which ferments, the sugar, or rather the sugars, the products of fermen- tation, among which alcohol takes its place in the first rank, and then the determining cause of the fermenta- _ tion of sugar, beer-yeast. PRODUCTS OF THE REACTION. Let us first consider alcoholic fermentation as an ordinary chemical reaction ; in other words, let us study it by means of the body which is decomposed, and the products which are derived from it; we will then consider the cause of the decomposition, and the pro- perties of this ferment, as well as those of analogous products. We said before that Becker was the first to recognize the necessity of the presence of sugar in wines which undergo spirituous fermentation, but that to Lavoisier belongs the honour of having studied and demonstrated the relations of their composition which connect sugar with its derivatives. Setting out with this principle, that nothing is created either in the operations of art, or in those of nature ; that in every operation there is an equal quantity of matter both before and after the operation; that the | 20 ON FERMENTATION, quality and quantity of the elements are the same, and that there are only changes and modifications, this illustrious:chemist established by analysis the centesi- mal proportions of carbon, hydrogen, and oxygen contained in sugar, operating in the same manner on the alcohol, the carbon dioxide, and acetic acid recog- nized by him as the products of the decomposition of sugar; then, estimating by analysis the respective quantities of these three bodies which are formed at the expense of a known weight of sugar, he ascertained the result of the reaction, and arrived at the following conclusions :— “ The effects of vinous fermentation are reduced to separating into two portions the sugar, which is an oxide, and oxidizing one at the expense of the other, so as to form from it carbon dioxide, in reducing the other in favour of the former, to form from it a combustible substance, alcohol ; so that if it were possi- ble to recombine these two substances, alcohol and carbon dioxide, we should reform the sugar.” He had really made a great advance on the conceptions of Stahl, founded on a mixture of salt, oil, and earth. The researches of Lavoisier may be summed up by the following equation :— 95'9 parts of crystallized cane sugar contain 268 of carbon, 7‘7 of hydrogen, and 61-4 of oxygen. These are decomposed, and form 57°7 parts of alcohol, containing 16°7 carbon, 96 hydrogen, and- 31'4 oxygen + 35°3 parts of carbon dioxide, contain- ing 9°9 carbon, and 254 oxygen+2°5 parts of acetic acid, containing 06 carbon, 02 hydrogen, and 1°7 oxygen. Digitized by G O08 le ALCOHOLIC OR SPIRITUOUS FERMENTATION. 21 Thus we find :— Carbon of the sugar. . . 268 Hydrogen , 4, « . . - 77 Oxygen » 9 8 8 . - 614 Sum of carbon of the three products 27°2 » 9 hydrogen ” ” 98 » » Oxygen ” ” 58°5 Taking into consideration the imperfections of his method of analysis, Lavoisier thought the agreement between the two sides of this equation sufficient to confirm the general principle announced above. If we compare with these numbers those furnished by the wonderfully accurate methods employed by modern chemists, we shall see that, in reality, 95°9 parts of cane sugar contain :— 44°4 carbon, 6°1 hydrogen, and 494 oxygen; and give, 51°6 of alcohol, containing— 26'9 carbon, 6'7 hydrogen and 180 oxygen + 49°4 parts of carbon dioxide, containing— 13°5 carbon, and 369 oxygen. It was therefore only by compensation of consider- able errors that Lavoisier was led to an approximate solution. . Towards 1815, the analyses so carefully made by Gay-Lussac and Thénard, and by De Saussure, settled in a determinate manner the composition of sugar and of alcohol. These results, far from invalidating the ~ conclusions of Lavoisier, gave them solid support. Thus Gay-Lussac (Ann. de Chimie, vol. 95, p. 318) wrote: “If it be supposed, now, that the products 22 ON FERMENTATION. furnished by the ferment can be neglected, as far as relates to the alcohol and carbonic acid which are the only sensible results of fermentation, it will be found that, given 100 parts of sugar, 51°34 of them will be converted during fermentation into alcohol, and 48°66 into carbonic acid.” These results, expressed in a chemical equation,* give to cane sugar the formula C,, Hy, O,,,f and we shall have C,, H, O,, = 4C,H, O, + 4 CO,t The analyses of cane sugar made by Gay-Lussac and Thénard themselves agree, as well as those since made by a great number of chemists, with the formula Cyp Hye Oy,§ In order to arrive at the error which we have just pointed out, and which Messrs, Dumas and Boullay showed in 1828, Gay-Lussac supposed that his analyses of cane sugar were imperfect, and he modified them recklessly, in the proportion of 2 or 3 per cent., in order to establish an agreement between the two sides of his equation. “The theory of fermentation arrived at by Gay- Lussac is still imperfect,” said Messrs. Dumas and Boullay, “but it is no longer so when we substitute ether for alcohol in the theoretical composition of sugar. The most complete agreement is then established between theory and experiment.” The conclusion which these two chemists deduced from this obser- * These formulze are given by M. Schtitzenberger as original formulas. It may be worth while, from an historical point of view, to preserve them as written by their enunciators, in the ‘* old notation,” thus :— $F CoHe% FCs Hy On = 2 C, Hy 0, + 4 CO, § Cy Hy Op. Digitized by G O08 le ALCOHOLIC OR SPIRITUOUS FERMENTATION. 23 vation, was that cane sugar cannot ferment without assimilating the elements of a molecule of water. In other words, Gay-Lussac’s equation, as a numerical expression, is correct, but that it would be better to write the first member of it under the form— Cig Hog Oy, + H, O = 4C, H,O + 4 CO,* cane sugar water alcohol _ carbon dioxide. A little later (1832), Dubrunfant observed that before fermentation commenced, the cane sugar is transformed into uncrystallizable sugar. M. Berthelot proved afterwards that the taking up of water by the cane sugar which precedes alcoholic fer- mentation is due to the presence of a soluble ferment in the yeast ; we shall return again to this important point. Finally, in 1833, Biot discovered the change of sugar under the influence of acids. Gay-Lussac’s equation, modified by Dumas and Boullay, was generally admitted for more than twenty years, as the mathematical expression of the decom- position of sugar by yeast. Meanwhile, in 1856, Dubrunfant, by making a quan- titative analysis of the carbon dioxide disengaged by fermentation, observed that it was not possible to make experimentally the equation of fermentable sugars with alcohol and carbon dioxide only. (Comp. Rend. de l’Acad. des Sciences, vol. 42, p. 945.) ’ The latest important work on the qualitative and quantitative analyses of the products of the alcoholic fermentation of sugars is due to M. Pasteur. (Ann. * Cy Hy On + HO = 2 C, H, 0, + 4 CO, cane Sugar _— water alcohol _ carbon dioxide. | 24 ON FERMENTATION. Chimie et Physique, 3rd series, vol. 58, p, 330.) Bya series of very interesting researches, and by irrefutable experiments, this illustrious chemist proves: 1st. That in every alcoholic fermentation, besides the principal products, alcohol and carbon dioxide, glycerin and succinic acid are formed; 2nd. That the glycerin and succinic acid are produced at the expense of the ele- ments of the sugar, and that the ferment takes no part in it; 3rd. That, besides this, the sugar yields a certain portion of its substance to the new ferment which is developed ; we shall return to the last point when we more especially consider the ferment; 4th. That the lactic acid, the production of which, in variable quan- tities, has been observed in alcoholic fermentation, is the result of a special fermentation, differing from alcoholic fermentation, and proceeding simultaneously with it. Let us say, in conclusion, in order to give to every one his due, that the presence of succinic acid in fer- mented liquids had been observed, before M. Pasteur, by Dr. Schmidt of Dorpat (Handwérterbuch der Chimie, Von Liebig, Poggendorff, 1st edit., vol. 3, p. 224, 1848), and also by Schunck in the fermentation of sugar by means of erythrozyme, the ferment derived from madder. These facts had passed unperceived, and had been forgotten, at the time when Pasteur returned to the study of this subject. Without entering into the details of the experiments on which Pasteur’s conclusions rest, and which will be found in his memoir (loco citato), we will simply give the results of his quantitative researches. Digitized by G O08 le ALCOHOLIC OR SPIRITUOUS FERMENTATION. 25 100 parts of can