YEASTS AND MOLDS 221 



characteristic taste to the beer. Brewers, by paying special 

 attention to the nutrient media, cultivate yeasts which give 

 to their beers individual flavors. 



Mixed yeast gives rise to a poor quality of beer. 



Saccharomyces Rosaceus; S. Niger; S. Albicans. 

 These yeasts are found in the air; and instead of producing 

 alcoholic fermentation, they give rise to a pigment in the 

 culture-media. They grow upon gelatin, which they do not 

 liquefy. 



Fig. 108. Yeast-cells ( X 500) (Frankel and Pfeiffer). 



Saccharomyces Mycoderma. This yeast forms a mold- 

 like growth, or skin, on the surface of fermented liquids, but 

 does not cause any fermentation itself. It forms the common 

 "mold" on wine, preserves, and "sauer-kraut." 



Oidium. A form which seems to be the bridge between 

 the yeast and the molds is the oi'dium. Sometimes it re- 

 sembles the yeasts, sometimes the molds, and often both 

 forms are found in the same culture. Several are patho- 

 genic for man. 



