TOP-FERMENTATION YEASTS. . 339 



Acid-production : 6-5. 



Odour good, but bitter, persistent taste. 



9. (Fig. 66, e, and Fig. 67, e.) 



During fermentation a very uniform growth of big, round 

 and oval cells. 



The yeast lies rather loose in flask ; on shaking, the cells 

 are distributed equally throughout the liquid. 



Film-formation : In 31 to 32 days very slight, isolated 

 patches on the surface, and a slender ring of yeast cells on 

 the glass, round the edge of the liquid. 



The cells of the film differ but little from those of the 

 fermentation. 



If developed at a low temperature, the spores are medium 

 in size and granulated. At 11 to 12 C. spore-formation sets 

 in on the ninth day ; at 25 C., for forty hours, a somewhat 

 scanty spore-formation takes place, accompanied by a con- 

 siderable formation of net-work. 



When the principal fermentation was broken off, the liquid 

 contained 2-96 per cent, by vol. of alcohol ; during the following 

 two periods 1-19 and 0-00 per cent, by vol. were formed. 



Acid-production : 7. 



Odour good, pronounced vinous taste. 



Regensburger has since undertaken very detailed com- 

 parative experiments with regard to three species of top- 

 fermentation yeasts, which, like the examples just referred 

 to, display characteristic differences in the general appearance 

 of the young growths. Spore-formation occurs within differing 

 periods, and conforms to the rule laid down by the author many 

 years ago that the development of spores usually takes place 

 more rapidly with top yeasts than with bottom yeasts. 

 Distinct points of difference can also be observed in the visible 

 course of fermentation, in the cardinal points for skin formation 

 and in the development on solid substrata. 



I At the time, the author's argument that purely-cultivated 

 top yeasts would quickly become impure on account of the 

 prevailing high temperatures was subjected to criticism. Ex- 

 perience has shown that these criticisms have no weight, 



