174 A MANUAL OF BACTERIOLOGY 



by gemmation or budding, but they can also produce 

 spores, especially when they are deprived of nourish- 

 ment. These organisms occur widely distributed 

 in air, soil, and water, and they are the cause of the 

 alcoholic fermentation. 



Saccharomyces cerevisice. This organism is some- 

 times termed Torula cerevisice, and is the true fer- 

 ment of beers. The cells are round or oval (8 to 

 fj, long), and are either isolated or united in small 

 colonies. The spore-forming cells (when isolated) 

 measure from 11 to 1 4 //, long ; and the spores mea- 

 sure from 4 to 5 fi in diameter. This organism occurs 

 in beers brewed by both the high or low systems of 

 fermentation. Fig. 39, 1 and 2, represent the beer- 

 ferments. There are two races of this species, high 

 (1) and low (2) yeasts. The cells of high yeast are 

 slightly larger and more round than those of low yeast. 

 Low yeast never rises to the surface of the fermenting 

 wort, which is kept at a temperature varying from 

 4 to 5 C. This low fermentation is a slow process, 

 occupying about fourteen days. The low fermenta- 

 tion gives rise to ' Lager ' or ' Bavarian ' beer. High 

 yeast rises to the surface as the fermentation pro- 

 ceeds, and the wort is kept at a temperature varying 

 from 16 to 20 C. The fermentation is rapid, and 

 rarely occupies more than a few hours or so. The 

 high and low yeasts are not different species. Both 

 high and low yeasts secrete a soluble enzyme which 

 converts maltose and sucrose into invert sugars 

 (dextrose and levulose) : 



C I2 H 22 O n + H 2 = C 6 H I2 6 + C 6 H 12 6 . 

 [maltose] [dextrose] [levulose] 



