266 MICRO-ORGANISMS AND FERMENTATION. 



ship to its fermentative power, but a certain uniformity 

 appears to exist among the yeast species in their action on 

 any given wine. 



A complete alteration of the fundamental character of a 

 wine by the use of pure cultures of wine yeasts is impossible, 

 but by a suitable selection of species and the right method of 

 application important advantages can be secured in every 

 case. The same applies to the different kinds of fruit wines, 

 which may be fermented both with grape wine yeasts and 

 with pure cultures of the species growing on the respective 

 fruits. 



Kayser compared the chemical properties of several types 

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

 at higher temperatures differed for each species. Thus, with 

 a rise in temperature, the quantity of these acids increased 

 in one species and decreased in another. 



Forti, basing his conclusions on comparative experiments 

 with wine yeast, has drawn attention to the existence of 

 typical differences in the fermentative power of the species, 

 power of resistance to high temperatures, and both quantity 

 and quality of the nitrogenous constituents required in the 

 nutritive liquid. According to his view, there is a well- 

 marked distinction in the character of the fermentation 

 produced by yeasts in the primary or vigorous fermentation, 

 on the one hand, and those of the secondary or quiet ferment- 

 ation on the other. 



The numerous investigations carried out continuously 

 since 1884 in the author's laboratory with pure cultures of 

 yeasts, as applied in the various branches of the fermentation 

 industry, have furnished ample opportunit}'- for collating 

 experience relating to the chemical activity of species, and 

 to their respective powers of retaining their peculiarities 

 intact during storage, a matter of importance to every branch 

 of the industry. Numerous instances have been met with 

 in which even feebly-pronounced characters, manifested 

 through taste or smell, remain inherent after several years' 

 preservation of the growth ; they may be restored by suitable 

 development of the culture under favourable circumstances. 



