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THURSDAY, JANUARY 18, 1877 



FERMENT A TION > 

 II. 



Etudes sur la Biere. Par M, L. Pasteur. (Paiis : 

 Gauthier- Villars. ) 



WHAT is fermentation ? Such is the important 

 question of which we have now to seek the 

 solution. It is necessarily impossible within the scope 

 of a brief article to enter into an examination of the 

 numerous theories propounded, yet a few words of ex- 

 planation are needed in order that we may the more 

 clearly understand what it is that Pasteur has done, and 

 what is the real bearing of his answer to the question 

 not only on fermentation, but on many a disease which 

 flesh is heir to. 



According to Willis and Stahl, to whom we are in- 

 debted for the first philosophical attempt at explanation, 

 fermentation was due to a peculiar motion communicated 

 from a decaying body to another substance, by which a 

 similar degrading action was set up, so that complex mole- 

 cules became less complex. This idea was subsequently 

 taken up and developed by Gay-Lussac, Liebig.and others, 

 who maintained that the decomposition of albuminous 

 bodies produced the molecular disturbance by which sugar 

 was broken up into alcohol and carbonic acid. Thus the 

 molecular disturbance produced by decay of nitrogenous 

 matter in a fitting liquid gave rise to lactic and butyric 

 acids and other products. 



The contact theory of Berzelius and Mitscherlich be- 

 longed to a period in the history of chemistry when cata- 

 lysis was constantly employed to explain the unknown, 

 and need not here be further alluded to. 



Cagniard de Latour, in 1837, first proved that yeast is 

 composed of living cells ; this was confirmed by the almost 

 contemporaneous observations of Schwann and Kiitzing, 

 and subsequently by Turpin and others. The subject, how- 

 ever, remained in much obscurity until Pasteur commenced 

 his investigations on the nature of ferments ; these have 

 been carried on for a period of twenty years, the results ob- 

 tained being communicated to the French Academy in 

 1862 and subsequent years and are now, in so far as they 

 concern the brewer, summed up in the important work 

 before us. The theory of molecular disturbance produced 

 by putrefaction, so energetically maintained by Liebig, 

 may be considered vanquished on all points. M. Pas- 

 teur, from his researches, has proved incontestably the 

 two following propositions : — 



1. Every diseased alteration in the quality of beer coin- 

 cides with the development of microscopic organisms 



foreign to the nature of beer, properly so called. 



2. The absence of alteration of beer wort and of beer 

 coincides with the absence of foreign organisms. 



The first proposition M. Pasteur has amply proved from 

 hundreds of examinations of beer undergoing diseased 

 action ; in no one case did he find the sediment of such 

 beer to consist solely of the globular or ovoid alcoholic 

 yeast cells, but of a more or less intermixture with the 

 various ferments of disease already described by him with 

 great minuteness in his " Etudes sur le Vin." His second 

 proposition is a necessary corollary of the first. 



' Continued from p. 216. 



Vol. XV. — No, 377 



We cannot do better than follow our author in some of 

 his researches by which he has demonstrated the truth of 

 these propositions. M. Pasteur, by boiling animal and 

 vegetable infusions —it is not necessary in all cases to use 

 so high a temperature — and then, by cooling them under 

 rigid precautions against the introduction of germs from 

 the air, has shown that they are then unacted, upon by 

 oxygen, at least that no putrefaction or fermentation 

 ensues. 



The temperature to which a liquid must be heated in 

 order to ensure against subsequent decomposition varies 

 with its nature. Thus while 50° C. is sufficient to destroy 

 the germs in vinegar, malt infusion must be heated to 

 90° C, and milk to 110° C, and others require even 

 higher temperatures. Blood and urine heated in Pasteur's 

 flasks and cooled under conditions precluding the entrance 

 of germs from the air undergo no alteration even when 

 kept for weeks at a temperature of 20° C. in contact with 

 pure air. Mere oxidation therefore is not the cause of 

 fermentation and putrescence. It is unnecessary to refer 

 to the exceptions taken by many experimentalists to 

 Pasteur's conclusions, the great experimental skill required 

 and the rigid precautions to be taken to secure success 

 amply explain why others less habile than Pasteur have 

 obtained conflicting evidence. Two of the ablest of his 

 opponents. Doctors Brefeld and Traubc, have recently 

 retracted their previous objections to Pasteur's results, 

 and now unhesitatingly adopt his views on Fermentation. 

 Allusion has already been made to the fact that the 

 brewer occasionally, and the wine grower invariably, 

 leaves the saccharine liquid to spontaneous fermentation ; 

 it is many years since Pasteur first demonstrated that the 

 dust on the skin of the grape contained the small organisms 

 necessary for vinous fermentation, and that when these 

 were destroyed or removed no fermentation took place. 

 Thus the juice heated in a Pasteur flask with the usual 

 precautions against the admission of germ-laden air did 

 not undergo fermentation when freely exposed to germ- 

 free air, but did so readily when a portion of the dust of 

 the skin was added. If this dust, however, was removed 

 by a few drops of water and then boiled previously to 

 being added to the must no fermentation took place. 

 Hence the dust on the skin contained the ferments, 

 and M. Pasteur has demonstrated their nature and their 

 distinguishing features. 



In the case of boiling beer wort there are necessarily 

 no living organisms, and therefore, as Pasteur has shown, 

 there is no change when the wort is allowed to cool in a 

 vessel to which only pure air has access. If, however, 

 the cooled wort be exposed to air, ferments of various 

 kinds, e.g., Saccharomyces cerevisice (though rarely), 

 Sacchorofnyces pastorianus, and apiculatus, and other 

 alcoholic ferments, fall into the liquid ; at the same time, 

 however, attended by more or less of the lactic and 

 butyric ferments and other organisms of disease. In a 

 brewery where other fermentations are proceeding, doubt- 

 less the number of alcoholic ferments will be greater and 

 the injurious bacteria less than in other localities ; still 

 in any case the beer when finished must be very inferior 

 owing to the large quantities of acetic, lactic, and butyric 

 acids, and other products of putrefactive change. M. 

 Pasteur, having satisfactorily demonstrated that alcoholic 

 fermentation was due to the action of certain organisms 



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