YEASTS 75 



Many true yeasts are more or less injurious. They do not, like 

 bacteria and pseudo-yeasts, cause serious diseases, capable of completely 

 ruining the fermented product, but they may injure the quality more or 

 less. Some yeasts are useful in certain cases and injurious in others. 

 If beer yeasts become contaminated with wine yeast the resulting beer 

 may be persistently turbid. If one attempts to ferment grapes 

 with beer yeast, a wine with a disagreeable beer aroma and of poor 

 keeping qualities is produced. 



S. pasteurianus occurs in several forms as an injurious yeast in brew- 

 eries, causing bitterness and turbidity. Similar forms occur in wine but 

 do little harm except in the absence of the true wine yeast. The cells of 

 this species vary from oval to long ellipsoidal, often being much elon- 

 gated and in film formation sometimes producing a branching mycelium. 

 Spores are formed easily and abundantly. 



The apiculate yeast, S. apiculatus, is very abundant on grapes and 

 most acid fruits. It is very variable and undoubtedly includes many 

 varieties. The cells are small, vary in shape from oval to cylindrical, 

 most of them having an apiculation at one or both ends, making them 

 pear or lemon shaped. According to Lindner they form spores in drop 

 cultures, one in a cell. Under favorable conditions this yeast increases 

 with great rapidity, but is checked by 3 to 5 per cent of alcohol. It 

 causes cloudiness in wine, interferes with the growth of the proper 

 yeast and injures the flavor. 



Many yeasts, mostly small and some of them rose-colored, have 

 been found on grapes and in wine, but they do not develop under 

 ordinary conditions of wine making sufficiently to be harmful. 



Schizosaccharomyces pombe is a yeast found in pombe or millet beer, 

 made by negroes in Africa. It is cylindrical and large, though variable 

 in size. Both ends are rounded. It multiplies by forming a septum 

 near one end, the smaller division then growing into a normal cell. 

 From one to four spores are formed in a cell. These spores are often 

 produced in the fermenting liquid. The fermentative power is high and 

 a large percentage of alcohol may be formed. 



Several other species of this genus have been isolated from grapes 

 and from Jamaica rum. 



PSEUDO YEASTS. Budding cells often occur in fermenting liquids 

 which have all the characteristics of yeast except that of producing 

 endospores. They are grouped together under the name of Torula. 



