BREWERY YEASTS. 319 



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 to yeast-turbidity. 



By far the greater number of high-fermentation yeasts 

 examined in this respect are able to carry through a secondary 

 fermentation. In class 2, and especially 3, the secondary 

 fermentation is very vigorous and long continued. 



Before the results of these comparative experiments had 

 been published, both Hansen and the author had had the 

 opportunity, as will be seen, of demonstrating that many of 

 the species so characterised appeared as strongly marked types 

 when applied in the form of mass cultures in practice, and 

 that both in the above and other respects typical differences 

 made their appearance between the individual races or species 

 which found application as culture yeasts. The experience 

 gained during the years that have since elapsed goes to prove 

 that by a methodical selection of a race, an element of cer- 

 tainty is introduced into the fermenting conditions, which was 

 impossible when a mixed yeast of unknown composition was 

 employed. 



In 1884 Hansen made the following pronouncement : 



" We find by closer investigation that differences exist 

 amongst the kinds of yeast which must be described as good 

 from the standpoint of the brewer. Thus, under similar con- 

 ditions, some give a quicker and more complete clarification 

 in the primary fermentation and a more feeble attenuation 

 than others. Again, differences are found in respect to flavour. 

 If my method is followed, it is possible, nevertheless, to select 

 with care and quite methodically, that species, which is best 

 suited for the particular work. This phase of the question has 

 been practically solved at Old Carlsberg, where a yeast has 

 been selected, in addition to that previously described, which 

 is better suited for making lager beer, whilst the former 

 is better for export beer. Where the fermentation industry 



