174 MICRO-ORGANISMS AND FERMENTATION. 



must, apart from the amount of nutrient ingredients existing 

 in the must, depends on the specific power of multiplying of 

 the yeast-type used ; on the other hand, it is in itself 

 independent of the origin or composition of the must. In 

 any given must, whether it be an excellent or an indifferent 

 nutrient medium for the wine yeast, one yeast type will 

 multiply more freely than another. , 



An extensive comparison of the amount of extract contained 

 in a number of wines fermented with three different yeast 

 species showed that in the same must the " Wiirzburg yeast " 

 consumed the smallest quantity of extract ; next came the 

 " Johannisberger," whilst the " Ahrweiler yeast " used up the 

 largest amount of extract, and, accordingly, left the smallest 

 residue in the wine. 



. The specific activity of wine yeasts manifests itself parti- 

 cularly in the formation of glycerine. These three species 

 were compared in a large number of musts of different origin, 

 and, generally speaking, the Wiirzburg yeast formed more 

 glycerine than the other two; of these the Johannisberger yeast 

 was superior to the Ahrweiler, which, as stated above, was 

 distinguished as the one fermenting the extract most satis- 

 factorily. The difference here shown to exist between the 

 chemical behaviour of these species was made still more 

 pronounced by the fact that the " Wiirzburg yeast " had 

 multiplied least. 



Both the amount of nitrogen and of ash proved to be 

 different in wines fermented with the three species of yeast. 



The amount of acid was highest in the wines fermented with 

 Wiirzburg yeast and practically equal for the other two species. 



Finally, in accurate comparative experiments, a large number 

 of species proved to differ widely with respect to the amount of 

 alcohol produced in the liquid ; those yeasts having the shortest 

 time of fermentation yielded the smallest amounts of alcohol, 

 and conversely. 



The question, whether the formation of special " bouquet " 

 substances in the individual type or species of wine yeast is 

 constant, or dependent on the character of the must, a question 

 of great technical importance, was answered in the affirmative 

 by WORTMANN ; for he has demonstrated the possibility (con- 



