The Diseases of Beer, Their Causes, and
the Means of Preventing Them

by
Louis Pasteur

Translated by
Frank Faulkner
and
D. Constable Robb

To
The Memory Of
My Father,
Formerly a Soldier under the First Empire,
And
Knight of the Legion of Honour.

The Longer I Live, the Better Do I Understand the Kindness Of
Thy Heart and the Excellence of Thy Mind.

To Thy Example and Counsels Do I Owe the Efforts That Have
Been Devoted to These Studies, as Well as to All the Work
I Have Ever Done. And Now, How Can I Better Honour These
Filial Remembrances than by Dedicating My Book to Thy Memory?

L. Pasteur.

Author’s Preface

Our misfortunes inspired me with the idea of these researches. I undertook them immediately after the war of 1870, and have since continued them without interruption, with the determination of perfecting them, and thereby benefiting a branch of industry wherein we are undoubtedly surpassed by Germany.

I am convinced that I have found a precise, practical solution of the arduous problem which I proposed to myself — that of a process of manufacture, independent of season and locality, which should obviate the necessity of having recourse to the costly methods of cooling employed in existing processes, and at the same time secure the preservation of its products for any length of time.

These new studies are based on the same principles which guided me in my researches on wine, vinegar, and the silkworm disease — principles, the applications of which are practically unlimited. The etiology of contagious diseases may, perhaps, receive from them an unexpected light.

I need not hazard any prediction concerning the advantages likely to accrue to the brewing industry from the adoption of such a process of brewing as my study of the subject has enabled me to devise, and from an application of the novel facts upon which this process is founded. Time is the best appraiser of scientific work, and I am not unaware that an industrial discovery rarely produces all its fruit in the hands of its first inventor.

I began my researches at Clermont-Ferrand, in the laboratory, and with the help, of my friend M. Duclaux, professor of chemistry at the Faculty of Sciences of that town. I continued them in Paris, and afterwards at the great brewery of Tourtel Brothers, of Tantonville, which is admitted to be the first in France. I heartily thank these gentlemen for their extreme kindness. I owe also a public tribute of gratitude to M. Kuhn, a clever brewer of Chamalières, near Clermont-Ferrand, as well as to M. Velten, of Marseilles, and to MM. de Tassigny, of Reims, who have placed at my disposal their establishments and their products, with the most praiseworthy willingness.

L. Pasteur.

Paris, June 1, 1876.

Preface to English Edition

My first idea of placing before English brewers a translation of “Études sur la Bière” was meagre in the extreme, compared with the final realization of it as it appears in the following pages.

Seeing the vast importance of Pasteur’s work from a practical point of view, after writing a review of it for the Brewers’ Journal, I determined to procure, at any rate for the use of my pupils, a literal translation, illustrated by photo-lithographic copies of the original plates, the thankless task of executing this preliminary translation for so limited a number of readers being most kindly and generously carried out for me by my friend Mr. Frank U. Waite, who, being engaged with me at the time in practical brewing operations, shared my views as to the value of the original work.

It was on the completion of this translation that my views and desires expanded. The more I studied the work, the more I was convinced of its immense value to the brewer as affording him an intelligent knowledge of the processes and materials with which he deals, but over and above all this, it was impossible not to feel that the researches of such a devoted and accomplished savant as Pasteur, possessed a scientific interest much wider than their mere relation to the art of brewing would imply. As the work of a skilful chemist and a laborious and accurate observer, such a protracted and careful study of the lowest and simplest forms of life, must necessarily be of first importance to the biologist — to the beginner as an admirable introduction to the study of practical physiology in general, as well as to the more advanced student, from the suggestive light which it throws on the nature of analogous phenomena in more complex organisms.

I determined accordingly to publish the work if I could secure the consent of its distinguished author, but at the same time I felt that the publication of M. Pasteur’s “Studies” in the form in which Mr. Waite had, at my request, translated it, and illustrated only with inferior copies of the original plates, would not be either advisable or just; but that I was bound rather to put the book before the English public in as satisfactory and complete a form as lay within my power. Under these circumstances I was induced to seek the aid of Mr. D. Constable Robb, B.A., of The Oxford University Museum, who, in taking Mr. Waite’s version as a basis, has so elaborated, annotated, and recast it, that I feel bound to say that much of the value of “Studies on Fermentation,” as it now appears, is due to the care that Mr. Robb has bestowed upon the revision that he so kindly undertook; a revision the result of which has created a feeling of confidence in the success of the translation as it now stands, which I could not have had in any mere literal version.

To the practical worker the original illustrations alone, which appear in this version, cannot but be of immense value in the microscopical study of the changes in the liquids with which he deals; whilst the many notes and additions, which are a feature peculiar to the English edition, more particularly the rendering into the equivalents, with which, unfortunately, practical men on this side of the channel are still most at home, of the metric weights and measures and centigrade temperatures, as well as the Index which Mr. Robb has compiled, will, I trust, render the book of still greater service than it otherwise would have been to many of those who may favour it with their attention.

The debt which we English brewers owe to M. Pasteur can hardly be over-estimated, and I must be allowed here to express my personal obligations to that distinguished worker for the permission which allows this translation; and to the French publishers for their help with regard to the interleaved illustrations.

The author’s preface and dedication are, of course, reproduced, the former making it unnecessary for me to refer more in detail to the contents of the translation.

Frank Faulkner.

The Brewery, St. Helen’s, Lancashire,
September, 1879.

Chapter I.
On the Intimate Relation Existing between the Deterioration of Beer, or the Wort from Which It Is Made, and the Process of Brewing

At the outset of these “Studies,” let us briefly consider the nature of beer and the methods of its manufacture.

Beer is a beverage which has been known from the earliest times. It may be described as an infusion of germinated barley and hops, which has been caused to ferment after having been cooled, and which, by means of “settling” and racking, has ultimately been brought to a high state of clarification. It is an alcoholic beverage, vegetable in its origin — a barley wine, as it is sometimes rightly termed.

Beer and wine, however, differ widely in their composition. Beer is less acid and less alcoholic than wine; it holds more ingredients in solution, and the nature of these ingredients is by no means similar to that of those which are found in wine.

These differences in the component parts of wine and beer give rise to corresponding differences in the keeping qualities of the two liquids. The small amount of acidity in beer, its poverty in alcohol, and the presence of matter that is saccharine, or liable to become so, all operate in imparting to beer a tendency to change, which wine does not possess. That this unequal resistance to the aggression of diseases is due to such differences, may be proved by the fact that wine could be made much more liable to change than it actually is, by a diminution of its acidity and its usual proportion of alcohol, or by increasing the proportion of viscid or saccharine matters, modifications which would tend to assimilate its composition to that of beer.

We have remarked elsewhere that the pains devoted to the rearing of vines, and to the ordinary operations of vinification, such as ouillage, sulphuring, and repeated rackings, as well as the use of cellars and vessels hermetically closed, are entailed by the necessity of counteracting and preventing the diseases to which wine is liable. The same may be said, a fortiori, of beer, inasmuch as it is more liable to change than wine. Manufacturers and retailers of this beverage have to strive constantly with the difficulty of preserving it, or the wort used in its manufacture. We may readily be convinced of this by reviewing the usual processes of the art of brewing.

When the infusion of malt and hops, which is termed wort, is completed, it is left to cool. It is next put into one or more casks or vats, in which it is made to undergo alcoholic fermentation — the most important of all the processes in brewing.

The cooling must be as rapid as possible. This is a condition of success; otherwise, the wort may deteriorate, which will necessarily lead to deterioration in the quality of the beer. As long as the wort is at a high temperature it will remain sound; when under 70° C. (158° F.), and particularly when at a temperature of from 25° C. to 35° C. (77° F. to 95° F), it will be quickly invaded by lactic and butyric ferments. Rapidity in cooling is so essential that to secure it recourse is had to special apparatus. Even in the preparation of wort, especially when it is effected by successive mashings, in summer, deterioration is imminent: in fact, it is not rare to see the wort becoming acid during the mashes, if these are not accomplished with all possible celerity.

After the wort has been cooled, it is mixed with yeast. This is obtained from a previous fermentation, and, after being thoroughly pressed, is added at the rate of from one to two thousandth parts of the weight of the wort, that is, from 100 to 200 grammes per hectolitre (about 4 oz. to 8 oz. average for every 25 gallons). At first sight, this yeast seems free from the possible diseases of the wort and beer; but this is by no means the case.

Now, why do we add yeast to our wort? This practice is unknown in the art of vinification. The must is always left to spontaneous fermentation. Why should we not leave the wort to operate in the same manner?

It would be a mistake to suppose that in the brewing of beer yeast is added with the sole object of accelerating fermentation, and making it more rapid. Rapidity in fermentation is a very questionable advantage, and one which is not desired by brewers, who rather agree in pronouncing it injurious to the quality of beer. It is in the easy deterioration of the wort, or what is tantamount to it, in the facility it affords to various spontaneous fermentations, that we find an answer to these questions. The must, through its acidity, due to the presence of bitartrate of potash — which seems to promote alcoholic fermentation — through its proportion of sugar, and perhaps in consequence of some other peculiarity of its composition, always undergoes regular alcoholic fermentation. The diseases of wine, at the commencement of its manufacture, show themselves, so to say, in a latent state only. Therefore a vintage can be left, without inconvenience, to spontaneous fermentation.

With wort the case is quite different. Under certain accidental circumstances it is possible that alcoholic fermentation alone may take place in a wort left to ferment spontaneously, and the quality of the beer remain unimpaired, but such an event would be exceptional, and of very rare occurrence. In most cases we should obtain an acid or putrid liquid resulting from the production and multiplication of alien ferments.

The addition of yeast is made in consequence of the necessity of exciting through the whole bulk of wort, as soon as it is cold, a single fermentation — viz., the alcoholic, the only one that can produce beer properly so called.

The alcoholic ferments concerned in the production of beer will be found represented in several of the engravings in this work. Other ferments we may term “diseased”; these include all those that may occur spontaneously — that is, whose germs have not been directly and intentionally introduced — amongst the actual alcoholic ferments.

The expression, “diseased ferments,” is justified by the circumstance that the propagation of these ferments is always accompanied by the production of substances which are acid, putrid, viscous, bitter, or otherwise unpalatable, a consideration of commercial rather than scientific importance. From a physiological point of view, all these ferments are of equal interest and importance. The botanist, as a man of science, in contemplating nature, must give equal attention to all plants, whether useful or noxious, since they are all governed by the same natural laws, among which no order of merit could be established. The exigencies of industry and health require, however, wide distinctions.

Plate 1. Principal Disease-ferments met with in Wort and Beer.

The first engraving (Plate 1) represents the different diseased ferments, together with some cells of alcoholic yeast, to show the relative size of these organisms.

No. 1 of the engraving represents the ferments of turned beer, as it is called. These are filaments, simple or articulated into chains of different size, and having a diameter of about the thousandth part of a millimetre (about 1/25000 inch). Under a very high power they are seen to be composed of many series of shorter filaments, immovable in their articulations, which are scarcely visible.

In No. 2 are given the lactic ferments of wort and beer. These are small, fine and contracted in their middle. They are generally detached, but sometimes occur in chains of two or three. Their diameter is a little greater than that of No. 1.

In No. 3 are given the ferments of putrid wort and beer. These are mobile filaments whose movements are more or less rapid, according to the temperature. Their diameter varies, but is for the most part greater than that of the filaments of Nos. 1 and 2. They generally appear at the commencement of fermentation, when it is slow, and are almost invariably the result of very defective working.

In No. 4 are given the ferments of viscous wort, and those of ropy beer, which the French call filante. They form chaplets of nearly spherical grains. These ferments rarely occur in wort, and still less frequently in beer.

No. 5 represents the ferments of pungent, sour beer, which possesses an acetic odour. These ferments occur in the shape of chaplets, and consist of the mycoderma aceti, which bears a close resemblance to lactic ferments (No. 2), especially in the early stages of development. Their physiological functions are widely different, in spite of this similarity.

The ferments given in No. 7 characterize beer of a peculiar acidity, which reminds one more or less of unripe, acid fruit, with an odour sui generis. These ferments occur in the form of grains which resemble little spherical points, placed two together, or forming squares. They are generally found with the filaments of No. 1, and are more to be feared than the latter, which cause no very great deterioration in the quality of beer, when alone. When No. 7 is present, by itself or with No. 1, the beer acquires a sour taste and smell that render it detestable. We have met with this ferment existing in beer, unaccompanied by other ferments, and have been convinced of its fatal effects.

No. 6 represents one of the deposits belonging to wort. This must not be confounded with the deposits of diseased ferments. The latter are always visibly organized, whilst the former is shapeless, although it would not always be easy to decide between the two characters, if several samples of both descriptions were not present. This shapeless deposit interferes with wort during its cooling. It is generally absent from beer, because it remains in the backs, or on the coolers; or it may get entangled in the yeast during fermentation and disappear with it.

Among the shapeless granulations of No. 6 may be discerned little spheres of different sizes and perfect regularity. These are balls of resinous and colouring matter that are frequently found in old beer, at the bottom of bottles or casks; sometimes they occur in wort preserved after Appert’s method. They resemble organized products, but are nothing of the kind. We have remarked before, in “Studies on Wine,” that the colouring matter of wine would settle, in course of time, in that form.

It is evident that the different ferments delineated in Plate I. are worthy of thorough study, in consequence of the fermentations to which they may give rise. Care must be taken to isolate the action of each of them in fermentations which we may call pure — a condition of some difficulty, but one that may be carried out by an adoption of the methods explained in this work.

All these diseased ferments have a common origin. Their germs, infinitesimal and hardly perceptible as they are, even with the aid of the microscope, form a part of the dust conveyed through the air. This dust the air is continually taking from or depositing upon all objects in nature, so that the dust that clings to the ingredients from which our beer is manufactured, may teem with the germs of diseased ferments.

During the process of fermentation, the occult power of diseased ferments, although it may escape the observation of the brewer, is manifested in a high degree.

During the last thirty years, or so, the art of brewing has undergone a radical change, at least in Europe. This change has been effected by a partial abandonment of the process of fermentation formerly used. Thirty years ago only one kind of beer was known; there are nowadays two distinct kinds — beer fermented at a high temperature, and beer fermented at a low temperature. Each of these is subdivided into many varieties, to which different names are given, according to their strength or colour. This is the case in England, where we find porter, ale, pale ale, stout, bitter beer, and other varieties of beer, although, as a matter of fact, the English have but one kind of beer, all the English beers being fermented at a high temperature.