186 STUDIES ON FERMENTATION. 



The sketch was made directly after the fermentation had 

 commenced. Probably this is simply one of the earlier forms 

 assumed by the saccharomyces, or by one of its varieties. It 

 will be seen that the alcoholic ferment is associated with another 

 little filiform ferment, probably the lactic. The spontaneous 

 ferments are almost always impure, a circumstance that may be 

 readily understood if we bear in mind the results described in 

 Chapters III. and IV. 



§ III.— On "High" and "Low" Fekments. 



The ferments mentioned in the preceding paragraphs do not 

 belong, properly speaking, to industrial products ; that is to say, 

 in actual practice there are no operations in which the ferments 

 of fruits and spontaneous ferments are employed for the pur- 

 pose. It is quite true that these ferments are the cause of the 

 fermentations from which wine, cider, gin, rum, gentiana, mead, 

 &c., are derived, but these fermentations are spontaneous, they 

 take place without the intervention of man, and without man's 

 directing their production, or taking any notice of the agent 

 whicb starts them. 



In the manufacture of beer, on the other hand, the practice is 

 quite different. We may say that the wort is never left to 

 ferment spontaneously, the fermentation being invariably pro- 

 duced by the addition of yeast formed on the spot in a preced- 

 ing operation, or procured from some other working brewery, 

 which, again, had at some time been supplied from a third 

 brewery, which itself had derived it from another, and so on, as 

 far back as the oldest brewery that can be imagined. A brewer 

 never prepares his own yeast. We have already had occasion 

 to remark that the interchange of yeasts amongst breweries is a 

 time-honoured custom, which has been observed in all countries 

 at all periods, as far back as we can trace the history of brewing. 

 The yeasts which in the present day produce beer in the 

 brewery of Tourtel, near Nancy, in that of Griiber, at Stras- 

 burg, that of Dreher, at Vienna, and others, came originally 



