TOP-FERMENTATION YEASTS. 341 



supposed that the secondary fermentation of stout is brought 

 about by certain species of Torula (two are described in the 

 systematic part of this chapter), and that it is due to their 

 activity that this variety of beer acquires its peculiar sourish 

 taste. Here, however, two separate facts have been confused. 

 The true secondary fermentation is carried out by the properly 

 selected type of yeast, and can be regulated like any other 

 secondary fermentation. In this connection the activity of the 

 Torulas is unnecessary, as may plainly be seen from the fact 

 that in every European country, and in other parts of the 

 world, as shown by the author, stout and similar kinds of beer 

 can be prepared from one -of certain selected types of yeast. 

 These species of Torula are to be reckoned in the same 

 category as the lactic - acid bacteria, acetic - acid bacteria, 

 Sarcina, etc., which also impart a special taste to a fermented 

 wort. If such a taste is desired, it is of importance to 

 regulate the activity of the organism in question, so that the 

 quantity of the peculiar fermentation or assimilation product 

 may stop short of a given limit. If this is exceeded the liquid 

 becomes undrinkable. 



It has frequently been suggested within recent times that 

 all the races of culture yeast present in an impure top- 

 fermentation yeast should be isolated and then again mixed in 

 the same proportion, with a view of using this culture mixture 

 in a brewery, where it would reproduce the original yeast, 

 freed from bacteria and wild yeasts. Such a process, however, 

 oould not be carried out, at any rate, in this world. 



After the author had introduced pure cultures into practice 

 in many European countries, the reform met with general 

 agreement. The work was taken up in the early stages by 

 Kokosinsky, de Bavay, M'Cartie, W. R. Wilson, A. Miller, and 

 R. Grey, to give but a few names. At a later stage, J. Schon- 

 feld attacked the problem, and selected types of top yeasts 

 were introduced into many German breweries, though chiefly 

 as pitching yeast and not as pure culture. 



In the case of top-fermentation lactic-acid beers, like 

 German "Weissbier," the rational treatment must consist in 

 the main in first carrying through a lactic-acid fermentation, 

 and then applying the pure-cultivated top yeast. 



