ALCOHOLIC FERMENTS. 175 



firmed by the writer's own experience), of imparting a special 

 bouquet to wine, and thus of essentially improving its taste, 

 and, consequently, enhancing its value in all those cases in 

 which indifferent musts with no prominent qualities are 

 fermented with specially-chosen pure yeasts. This also holds, 

 good when grape wine yeasts are used with fruit and berry 

 must. 1 



If the must itself contains a pronounced flavour, an added 

 yeast will not, of course, have a decided effect on the bouquet, 

 but its adoption will be justified by the greatly enhanced 

 purity and regularity of the fermentation. (See further on the 

 subject, Chapter VI.) 



KAYSER compared the chemical properties of several types 

 of wine yeast, and found the formation of volatile acids at 

 higher temperatures differed for each species. Thus the 

 quantity of these acids increased in one species, but decreased 

 in another, at a higher temperature. 



FORTI, basing his conclusions on comparative experiments- 

 with wine yeast, has called attention to the existence of typical 

 differences in the fermentative power of the species, in their 

 power of resistance towards higher temperatures, and in the 

 quantity and quality of the nutrient liquid they demand. 

 According to his view there is a well-marked distinction, in 

 the character of the fermentation produced by the yeasts of 

 the principal, or " vehement," fermentation on the one hand, 

 and those of the secondary or quiet fermentation on the other. 



The numerous investigations carried out continuously since 

 1884, in the author's laboratory, with pure cultures of alcoholic 

 yeasts, as used in the various branches of the fermentation 

 industry, have furnished ample opportunities of collating 

 experience relating to the extremely varied chemical activity 

 of the species and to their respective powers of retaining their 

 peculiarities intact during preservation, a matter of importance 



1 Considerable scientific and practical interest attaches to the much-debated 

 question, whether the amounts of alcohol and glycerine produced, bear any 

 certain proportion to each other. WORTMANN'S experiments, all conducted 

 with absolutely pure cultures, established the fact that this proportion is 

 subject to great fluctuations, even in one and the same type of yeast. Thus, 

 contrary to former assertions, no one definite proportion can be established as. 

 normal, e.g., in deciding whether a wine is adulterated or not. 



