FERMENTED FOODS AND DRINKS 213 



that the use of bottom yeast (Unterhefe) makes it easier to guard 

 against the entrance of wild yeasts and other objectionable 

 organisms. On the other hand it is claimed that the use of the 

 upper yeast (Oberhefe) yields a better quality of beverage. These 

 are factors of the greatest importance to the bacteriologists and 

 zymologists employed by the breweries but concern the food 

 bacteriologist but little. 



The following are some of the more important yeast organisms 

 concerned in alcoholic fermentation, giving the principal fermenta- 

 tive activities of each. Hansen's differentiation between the 

 genera Saccharomyces and Torula is based upon sporulation. 

 Saccharomyces forms spores (Ascospores; usually four spores in 

 each ascus or spore sac, rarely eight) whereas Torula does not 

 form spores. According to some authorities this is not a practical 

 basis of differentiation. 



Saccharomyces , 



cerevisea Hansen. A typical top yeast. 

 paslorianus, Hansen. A bottom yeast. 

 intermedius, Hansen. A rather feebly acting top yeast. 

 validus, Hansen. A top yeast. 

 ellipsoideus, Hansen. A typical bottom yeast. 

 turbidans, Hansen. A bottom yeast the cause of turbidity. 

 willianus, Saccardo. A flavor-producing yeast. 

 boyanus, Saccardo. Causes turpidity in beer and wine. 

 logos, van Laer. A bottom yeast developing a flavor. 

 thermanitonum, Johnson. A rapidly acting ferment. 

 ilicis, Gronlund. A bottom yeast; isolated from Ilex. 

 aquifolii, Gronlund. Also isolated from Ilex species. 

 pyriformis, Ward. Found in ginger beer. 

 vordermanni, W. and P. Isolated from Arrak. 

 sake, Yabe. Active in the fermentation of sake. 

 batata, Saito. In yam brandy. 

 cartilaginosus, Lindner. Isolated from Kephir. 

 muUisporus, Hansen. A top yeast. 

 mali, Kayser. A cider ferment. 

 marxianus, Hansen. A wine ferment. 

 exiguus, Hansen. In beer wort. 

 jorgensenii, Lasche. Causes turbidity. 

 zopfii, Artari. Found in syrup. 



