PRODUCED BY ALCOHOLIC FERMENTS. 223 



of yeast mixtures as definitely settled. My numerous ex- 

 periments with disease yeasts led me involuntarily to new 

 investigations in this direction, although from a different 

 point of view. The investigations may here be described, 

 which were undertaken with a view to decide the question 

 of the influence of mixtures of brewery yeasts on the stability 

 of beer. 



I. Series of Experiments. Four two-necked flasks of a liter capacity, 

 A, B, C, D, each of which was charged with 660 cc. of the same sterilised 

 and aerated lager beer wort, were infected with young vigorous growths 

 of the following yeasts : A with I cc. of Carlsberg bottom yeast No. i ; 

 B with i cc. of the bottom yeast from the Tuborg brewery, and which 

 was mentioned" above ; C with i cc. of the same Tuborg yeast and i cc. 

 of Carlsberg bottom yeast No. i ; and D with i cc. of Carlsberg bottom 

 yeast No. i and \ cc. of the Tuborg yeast. The yeast was in all cases 

 of a thick consistency. The primary fermentation took place at the 

 ordinary room-temperature, and when this was finished, it was found 

 that the beer in A and B had brightened satisfactorily, whilst the mixed 

 yeasts employed in C and D gave a less satisfactory result. The beer 

 was now transferred to other flasks, and stored at a temperature of 7 C. 



After remaining at this temperature for about a month and a half, A 

 and B were perfectly bright, and C and D, on the other hand, were opal- 

 escent. The beer was drawn off into small bottles in the manner already 

 described. After standing twelve days in bottle at the ordinary room- 

 temperature, A and B were bright and showed no yeast turbidity, C and 

 D were still slightly opalescent, and in both yeast turbidity was beginning 

 to manifest itself, and was distinctly noticeable in D. After two months' 

 storage C and D were less opalescent, but otherwise had remained practi- 

 cally unchanged. 



Thus, whilst in the case of each of the two brewery yeasts, 

 when employed separately and in pure culture, the brightening 

 was faultless, both as regards primary and after-fermentation, 

 and the beer was also stable, this was not the case when they 

 were mixed. 



A still more marked effect of the same character was 

 produced when the fermentation was effected by means of 

 a mixture of the Carlsberg bottom yeast No. i, and the top 

 yeast which I have named Sacch. cerevisice I. 



After the laboratory experiments had thus shown that, 



