YEASTS. 33 



5. pyriformis resembles in shape S. ellipsoideus, and in association 

 with Bacterium vermiforme produces ginger beer. 



S. vordermanni is concerned in the manufacture of arrack. It ferments 

 the sugar produced from rice by the molds, Mucor oryzcs and Rhizopus 

 oryza. 



S. fragilis and other yeasts have^ been found in kefir and other fer- 

 mented drinks made from milk. These yeasts working in conjunction 

 with bacteria produce alcoholic acid beverages. 



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 any 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 elongated and 

 in film formation sometimes producing a branching mycelium. Spores 

 are formed easily and abundantly. 



The apiculate yeast, 5. apiailatus, is very abundant on grapes, and 

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

 rieties. 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 cloudi- 

 ness 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 con- 

 ditions 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 



3 



