PRODUCED BY ALCOHOLIC FERMENTS. 227 



brief, mixed pitching yeasts may give rise to the irregularities 

 described. In an earlier part of this book I have in several 

 places discussed the question of the employment of mixed 

 yeasts from different points of view. 



These investigations furnish a further proof, that in the 

 brewery we should employ a pure culture of a single selected 

 race or species. 



Mycoderma cerevisia. 



As is known, this name is used to designate the yeast 

 cells which readily form films on beer and other alcoholic 

 liquids, but which do not develop endospores, and, there- 

 fore, do not belong to the Saccharomycetes. As with several 

 other names, so with this, the advance of science has shown 

 that the systematic name embraces not one but several spe- 

 cies. Some of these excite alcoholic fermentation, although 

 far less vigorously than the majority of the Saccharomycetes. 

 There are also some species of Mycoderma which, according 

 to recent investigations, produce sickness in low-fermentation 

 beers. I have been requested from several directions to give 

 an opinion on this question, and I believe this can best be 

 done in connection with the above investigations. 



When experimenting in the lager cellars of the Copen- 

 hagen breweries, Mycoderma cerevisice is everywhere met 

 with. This I pointed out, in 1878, in my investigations on 

 the micro-organisms of beer. In the years following I under- 

 took a very comprehensive study of the beer in the lager 

 casks of the Old Carlsberg brewery, including both the 

 ordinary lager beer and the export beer. The contents of 

 every cask contained a growth of the cells named, but, never- 

 theless, there was in no case any indication that the beer had 

 acquired any disease whatever from this cause. The cells 

 were, indeed, also frequently found when the beer was 

 especially characterised by a high degree of stability and 

 by a good flavour. 



