TOP-FERMENTATION YEASTS. 329 



Species of the second group behave quite differently. 

 Under similar conditions fermentation can be carried on for 

 a much longer time, clarification goes on slowly, and when the 

 primary fermentation is at an end the beer is decanted from 

 the yeast, which to a large extent is sedimentary yeast ; a 

 secondary fermentation takes place, the duration varying 

 according to the species. 



As representatives of the first group, the species chiefly 

 used in Danish breweries may be mentioned, and of the second 

 group, many of those applied in English breweries. 



The purely-cultivated Danish, top-fermentation species fall 

 into two distinct types, according to their chemical activity. 

 The first impart a decidedly mild flavour ; the fermentation 

 is weak without noticeable secondary fermentation, and the 

 layer of yeast forming on the surface of the liquid is loose 

 and slimy. The second type gives a strongly pronounced 

 flavour, the fermentation is stronger, with subsequent secondary 

 fermentation, and the layer of yeast has a dense consistency. 

 By long-continued use of both types the latter has proved to 

 be more generally acceptable. 



The English species that have been subjected to examina- 

 tion, and have been proved to bring about a distinct 

 secondary fermentation, exhibit a great variety of form and 

 various construction of spores. Many of these differences 

 have been recorded, both in these respects and in relation to 

 fermentation. According to the observations * of J. C. Holm 

 and the author, the following facts have been established : 



The formation of cells at the different stages of alcoholic 

 fermentation was determined by growths which were first 

 kept for a long time in a 10 per cent, sugar solution, then grown 

 for several generations in beer-wort, and finally developed for 

 twenty-four hours in Pasteur flasks at 25 C. The develop- 

 ment of the films and their appearance to the naked eye were 

 studied in growths in Erlenmeyer flasks at room temperature 

 (about 20 C.). Growths in Pasteur flasks at room temperature 

 were made use of for determining the physical character of 

 the sedimentary yeast. The fermentation experiments were 



* Published for the first time in Micro-Organisms and Fermentation, 3rd 

 edition, 1900. 



