PURE YEAST CULTURE. 263 



determined exclusively by the yeast, but that it is dependent 

 first and foremost upon the composition of the must. The 

 yeasts exert an influence on the taste, bouquet, and on the 

 whole character of the wine ; but it is too much to say that 

 a high-class Johannesberg wine, for instance, can be obtained 

 from an ordinary must by fermenting this with the yeast 

 from the wine named. According to Wortmann's more 

 recent investigations, the specific activity of the- yeasts is 

 prominently noticeable in the formation of alcohol and 

 glycerin. The view that the substances causing the bouquet 

 were due to the yeast was held even by some of Pasteur's 

 predecessors. But Wortmann's experiments were the first 

 to make this clear. He showed that each race of yeast has 

 the property of developing during fermentation its charac- 

 teristic bouquet substances, and that one yeast will produce 

 more and another less of these products. These being pro- 

 duced through the influence of the yeast, he terms them 

 secondary products, in distinction to the primary substances 

 which originate exclusively from the must. For the practical 

 application of the system of pure yeast culture, it is important 

 that the species of wine yeast show a similar constancy in 

 their physiological properties as in the case of brewery yeasts. 

 " It is thus possible," says Wortmann, " in institutions where 

 pure yeast culture is carried on, to select a number of pure 

 yeasts having definite properties, and such as are desirable 

 in practice, and these can then be supplied at any time, and 

 according to the purpose to which it is intended to apply 

 them." By means of selected species of yeasts, inferior must 

 may be made to yield better wines, in that a bouquet is 

 imparted to them which they would not otherwise acquire. 

 The fine must from the best kinds of grapes already contains 

 so much of the primary bouquet substances that there is here 

 little room for improvement ; the proper selection of the race 

 of yeast is, however, of great value also in this case, especially 

 as the valuable must is thereby insured against the destructive 



