408 



MICRO-ORGANISMS AND FERMENTATION. 



means of this macroscopic appearance Mycoderma is readily 

 distinguished from the ordinary Saccharomycetes, which, on 

 the same medium, form light greyish-yellow colonies with a 

 dry or lustrous surface, and a more or less arched form. Sacch. 

 membrancefaciens, which differs so markedly in its biological 

 behaviour, and which very rapidly gives a strong film on the 

 liquid, alone resembles Mycoderma in its behaviour on plate 

 cultures. 



This kind of film-formation was noted by Hansen when 

 lager beer had been exposed in open vessels at temperatures 

 between 2 and 15 C. ; at 33 C. development still occurred, 



but at temperatures above 

 15 C. this species gave place 

 more and more to competing 

 forms. As low temperatures 

 are favourable to its develop- 

 ment, it will readily thrive in 

 the storage cellar, especially 

 as lager beer forms a much 

 more favourable medium for 

 its growth than wort. This 

 is seen to be the case when 

 traces of a pure film are 

 introduced into lager beer 

 and w r ort, contained in open vessels, and then left to develop ; 

 the culture in lager beer nearly always remains pure, while 

 in wort various other species make their appearance. 



In Hansen's comprehensive experiments on Carlsberg beer, 

 it was always found that both lager and export beers were 

 attacked by this fungus ; but there was never the slightest 

 indication that the beer had acquired any disease from this 

 source. The fungus was widely distributed just at those 

 periods when the beer was found to be particularly stable 

 and of good flavour. This has also been confirmed by numerous 

 experiments on lager and export beers conducted by Gronlund 

 and A. Petersen, and those carried out in the author's labora- 

 tory. It is self-evident that we are only speaking of beer 

 which has been properly treated. In imperfectly closed 

 bottles and casks, Mycoderma cerevisice will of course rapidly 



Fig. 97. Mycoderma cerevisice from Copenhagen 

 brewerie^ (drawn from nature by Holm). 



