ACTION OF FUNGI ON CARBOHYDRATES, ETC. 2fi3 



on the second day, the fermentation of laevulose does not 

 reach its highest activity until later, in some species even as 

 late as the fifth day ; by slow degrees the proportionate 

 amounts of sugar fermented approach each other, and finally 

 both sugars disappear simultaneously. 



The yeast species also behave differently with regard to 

 the amount of acid produced in the nutrient liquid. From 

 this point of view Prior examined the fermentation products 

 of a number of brewery yeasts and wild yeasts in hopped wort, 

 and found that the amounts of acid formed varied from 4-7 

 to 10 c.c. of decinormal caustic soda solution per 100 c.c. of 

 fermented wort ; the fixed organic acids varied from 2-1 to 

 5-4 c.c., the volatile organic acids from 2-1 to 5-8 c.c. The 

 evidence shows that, in culture yeasts, the amounts of fixed 

 organic acids usually exceed those of volatile acids, whereas 

 in Hansen's wild yeast species (Sacch. Pastorianus I., II., and 

 ///., and S. ellipsoideus I. and //.) the reverse is the case, the 

 volatile acids exceeding the amount of the fixed acids ; this 

 is specially the case with Sacch. Pastorianus I. 



A large number of Saccharomycetes occurring in must 

 absolutely pure cultures of which were prepared by Hansen's 

 method were examined by Marx in 1888 both botanically 

 and with reference to their chemical action on the nutritive 

 liquid. They showed distinct differences in fermentative 

 power, and in their capacity for producing volatile substances 

 which impart a special bouquet to wine, and finally in their 

 power of resistance to different acids and to high temperatures. 



Amthor subsequently investigated a number of absolutely 

 pure cultures of wine yeasts, and detected typical differences 

 with regard to the time taken by the fermentation, as well 

 as in the chemical composition of the wines. Similar results 

 have also been obtained by Jacquemin, Rommier, Martinand, 

 and Rietsch in France ; Miiller-Thurgau in Switzerland ; 

 Wortmann and Nathan in Germany ; Mach and Portele in 

 Austria ; Forti and Pichi in Italy ; some of the comparative 

 experiments conducted by these authors having been carried 

 out on a large scale. 



The most thorough and extensive investigations into the 

 different behaviour of wine yeasts with regard to must are due 



