PRODUCED BY ALCOHOLIC FERMENTS. 211 



yeast, and in the wort contained in the fermenting vessels. 

 When Sacch. Pastorianus I. formed one-fifth of the pitching 

 yeast, the disease was produced in a marked degree ; on 

 diminishing the proportion it was less pronounced, and when 

 the wild yeast, or its varieties, formed % part of the total 

 pitching yeast, the disease could only just be detected. Under 

 the conditions described this appears, therefore, to be the 

 limit. A smaller quantity still will, therefore, scarcely have 

 any deleterious action in this direction. In an experiment 

 made with a strongly infected pitching yeast, it was found 

 that the beer still retained the disagreeable taste and odour 

 produced after no less than five months' storage. 



It was easy to foresee that beer which had been fermented 

 exclusively with a pure culture of this species, or its varieties, 

 must also acquire the same disagreeable taste and odour. 



When the infection only occurs in the lager casks, or in 

 the pipes leading to these, it is, under ordinary brewery con- 

 ditions, without effect. This is shown by the experiments 

 which were carried out partly with young vigorous growths 

 obtained by one day's cultivation in wort, and partly with 

 growths which, in conjunction with a brewery yeast, had 

 carried through a primary fermentation in a fermenting vessel 

 in the brewery. Only in the case of one experiment, in 

 which an extremely large proportion of a pure culture of 

 Sacch. Pastorianus I. was added at the commencement of 

 storage, did the beer acquire a faint indication of the disagree- 

 able bitter taste. 



An equally insignificant effect was produced when the 

 infection occurred at the end of the storage period. 



It is, however, not merely as regards taste and odour, but 

 also as regards the stability of the beer, that Sacch. Pas- 

 torianus I. can act injuriously. In the experiments in which 

 this species was present in the pitching yeast, it also interfered 

 with the brightening of the beer at the end of the primary 

 fermentation. Even when Sacch. Pastorianns I. formed only 



r 2 



