224 STUDIES ON FERMENTATION. 



beer, during the winter months, for consumption in summer, 

 up to August and September, are very anxious to prevent the 

 development of a vinous flavour in beers of this kind. Accord- 

 ing to our observations, this vinous flavour seems to be prin- 

 cipally due to an intermixture with the pitching yeast of 

 saccJiarornyces paHtorianus or its varieties, one of the peculi- 

 arities of which ferment is that in the course of time it imparts 

 a decided vinous flavour to beer. If this ferment were not 

 present amongst the yeast-cells — and here we are speaking of 

 an absolute, so to say, mathematically absolute absence — the 

 beer produced would gradually grow old in the store cellars, 

 without ever acquiring any vinous flavour, properly so called. 



This vinous flavour develops more especially in English 

 beers when these are kept. It is an easy matter to show 

 that in English beers, after their manufacture, saccJiaromyces 

 postorianus and the ferment which we have termed caseous, 

 which also imparts a peculiar flavour, form almost exclu- 

 sively, notwithstanding the fact that the yeast used in the 

 manufacture of English beer is a ferment essentially distinct 

 from saccharomyces pastorianus. 



The secondary fermentation which takes place in " high " 

 and " low " beers stored in cask after manufacture, is very 

 often due to this same ferment, which may be recognized 

 by elongated jointed cells, at times more or less ramified, 

 as well as by the influence which it exercises upon the flavour 

 of the beer. 



We may add that the general result of our researches has 

 convinced us that " high " yeast cannot transform itself, any 

 more than " low " yeast can, into the ferment of which we 

 are speaking, and that whenever a beer produced by means 

 of "high" or "low" yeast develops a foreign ferment, 

 this ferment must have existed in the original yeast in the 

 form of germs, which, from their extreme scarcity, often ftiil 

 to be detected by means of the microscope. The best proof 

 that we can give of this is the fact that a beer produced by 

 means of "high" or "low" yeast, if left to itself for months 



