608 MICROBIOLOGY OF ALCOHOLIC FERMENTATION 



Many other yeast-like organisms may occur on grapes, but, under 

 ordinary conditions, fail to develop sufficiently in competition with 

 apiculatus to have any appreciable effect on the wine. Most of them 

 are small round cells, classed usually as Torulce. They destroy the 

 sugar but produce little or no alcohol. 



A group of similar forms, known collectively as Mycoderma vini, 

 occurs constantly on the grapes. These, being strongly aerobic, do not 

 develop in the fermenting vat, but under favoring conditions may be 

 harmful to the fermented wine. 



BACTERIA of many kinds occur on grapes as on all surfaces exposed 

 to the air. Most of these are unable to develop in solutions so acid as 

 grape juice or wine. Of the acid-resisting kinds, a number may cause 

 serious defects and even completely destroy the wine. These, the 

 "disease-producing bacteria" of wine, are mostly anaerobic and can 

 develop only after the grapes are crushed and the oxygen of the must 

 exhausted by other organisms. Practically all grape must contains 

 some of these bacteria, which, unless the work of the wine maker is 

 properly done, will seriously interfere with the work of the yeast, thus 

 causing injury to the wine. The only bacteria which may injure the 

 grapes before crushing are the aerobic, acetic bacteria, which may 

 develop on injured or carelessly handled grapes sufficiently to interfere 

 with fermentation and seriously impair the quality of the wine. 



THE MICROORGANISMS FOUND IN WINE 



Wine microorganisms may be conveniently divided into two groups: 

 those which grow only in the presence of notable supplies of free 

 oxygen, and those which require, or grow better in, the absence of free 

 oxygen. 



AEROBIC ORGANISMS. Mycodermce. If a normal wine, especially 

 one strong in alcohol, is left with its surface exposed to the air, it will 

 usually, in a few days, be covered with a whitish film, thin and smooth 

 at first but gradually becoming thicker and finally rough and plicate. 

 This is what is known to wine-makers as " wine flowers" This film con- 

 sists of yeast-like cells, somewhat longer and more cylindrical than S. 

 ellipsoideus, reproducing by budding and forming large aggregations. 



Pure cultures show that there are many varieties of this organism 

 differing in the color and texture of the film, in the cloudiness of the 

 liquid and in the character of the deposit. They are called collectively 



