422 MICROBIOLOGY OF SPECIAL INDUSTRIES. 



at the beginning of the vintage and with acid grapes, is, therefore, often 

 almost entirely the work of the apiculate yeast. 



The amount of alcohol produced by this yeast is about 4 per cent, 

 varying with the variety from 2 to 6 per cent. When the fermentation 

 has produced this amount of alcohol the activity of the yeast slackens and 

 finally stops, allowing the more resistant ellipsoideus to multiply and 

 finish the destruction of the sugar. The growth of S. apiculatus, 

 however, has a deterring effect on that of the true wine yeast so that 

 where much of the former has been present during the first stagesof 

 fermentation the latter often fails to eliminate all the sugar during the 

 last stages. 



Wines in which the apiculate yeast has had a large part in the fer- 

 mentation are apt to retain some unfermented sugar and are very liable 

 to the attacks of disease -producing organisms. Their taste and color are 

 defective, often suggestive of cider, and they are difficult to overcome. 

 This yeast attacks the fixed acids of the must, the amount of which is 

 therefore diminished in the wine, while on the other hand the volatile 

 acids are increased. 



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

 ordinary conditions, fail to develop sufficiently in competition with apicu- 

 latus to have any appreciable effect on the wine. . Most of them are small 

 round cells, classed usually as Torula. They destroy the sugar but pro- 

 duce little or no alcohol. 



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

 occurs constantly on the grapes but, all being strongly aerobic, they 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 as 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 



