226 "DISEASES" OF BEER, 



in Result. In the cases investigated it was, therefore, 

 found that the beer was less stable when the pitching yeast 

 employed consisted of a mixture of two brewery yeasts, than 

 when only one species, no matter which, had been employed. 

 In these mixtures, the species present in smallest proportion 

 played the part of a disease yeast. The experiments teach 

 us that this not only occurred when the ratio of the two 

 mixed species was 9 to I, but also when the proportion was 

 19 to I, that is to say when only one-twentieth of the pitching 

 yeast consisted of a foreign brewery yeast. We are thus 

 confronted with the curious fact, that good brewery yeasts 

 can, as it were, modify their nature, and play the part of 

 disease yeasts. 



When we recollect that the Carlsberg bottom yeast No. 2 

 is a species which does not yield particularly stable beer, 

 there appears, indeed, nothing remarkable in the fact that 

 the addition of this species to a pitching yeast, consisting 

 mainly of Carlsberg bottom yeast No. I, has the effect of 

 rendering the resulting beer less stable than when the 

 fermentation has been effected by the latter species alone. 



On the other hand, it is remarkable that the addition of 

 Carlsberg bottom yeast No. I which, indeed, is characterised 

 by its yielding a stable beer to a pitching yeast consisting 

 mainly of the other species mentioned, should also cause 

 the resulting beer to be less stable than when fermented 

 with Carlsberg bottom yeast No. 2 alone. 



The effect described was only produced when the storage 

 of the beer was discontinued at a rather early stage, namely, 

 after I \ to if months ; after three months' storage there 

 was at most only a faint indication of instability. After 

 ij months, however, the beer was bright in all cases, and 

 where the No. 2 yeast had been employed it had the 

 appearance of a finished stored product. 



In breweries where yeasts are employed similar to the 

 last mentioned, and where the storage period is therefore 



