234 MICRO-ORGANISMS AND FERMENTATION. 



A. BOTTOM-FERMENTATION SPECIES. 



1. Species which clarify very quickly and give a feeble 



fermentation ; the beer holds a strong head. The beer, 

 if kept long, is liable to yeast- turbidity. Such yeasts 

 are only suitable for draught-beer. 



2. Species which clarify fairly quickly and do not give a 



vigorous fermentation; the beer holds a strong head; 

 high foam : the yeast settles to a firm layer in the 

 fermenting vessel. The beer is not particularly stable 

 as regards yeast-turbidity. These yeasts are suitable 

 for draught-beer and partly for lager-beer. 



3. Species which clarify slowly and attenuate more strongly. 



The beer is very stable against yeast-turbidity. These 

 yeasts are suitable for lager beer, and especially for 

 export beers. 



B. TOP-FERMENTATION SPECIES. 



1. Species which attenuate slightly and clarify quickly. 



The beer has a sweet taste. 



2. Species which attenuate strongly and clarify quickly. 



Taste of beer more pronounced. 



3. Species which attenuate strongly and often clarify slowly. 



The beer is stable against yeast-turbidity. 



By far the greater number of high-fermentation yeasts 

 examined in this respect are able to carry through a secondary 

 fermentation. In classes 2, and especially 3, this secondary 

 fermentation is very vigorous and long continued. 



As a very significant result of practical experience, and one 

 which shows how pronounced are the characters of many 

 species of cultivated yeast, it may be mentioned that, speaking 

 generally, the above grouping holds good, even under the different 

 practical conditions obtaining in widely separated countries. For 

 instance, the Carlsberg yeast No. 1 gives everywhere a beer 

 which is very stable as regards yeast-turbidity ; other species, 

 which clarify more rapidly, have been found to retain this 

 property everywhere under normal brewery-conditions. This 



