512 MICROBIOLOGY OF SPECIAL INDTJSTEIES 



Mycoderma vini, though one form which has been found to produce 

 endospores has been called S.anomalus. 



These organisms are strongly aerobic and can develop only on the 

 surface in full contact with the air. They are a serious enemy to the 

 wine, rendering it insipid and cloudy. They attack the extract, fixed 

 acids, and alcohol, producing at first volatile acids and finally causing 

 complete combustion of the organic matters to carbon dioxide and water, 

 destroying the wine completely. 



Acetic Bacteria. — ^The film formed on wines exposed to the air, 

 especially on those of low alcohohc content, will often differ from that 

 due to Mycoderma vini. It will be thinner, smoother and consist of 

 bacteria. These are the vinegar bacteria described on page 539. 

 They grow not only on the wine at the expense of the alcohol, but on 

 crushed grapes and must at the expense of the sugar, producing acetic 

 acid in both cases. 



Acetic acid in small amounts is produced by the yeast and is a 

 normal constituent of wine. Unless in excess its effect is not injiirious. 

 There may be, present from 0.12 g. in 100 c.c. in light white wine to 0.14 

 g. in a heavy red wine without deterioration of quality. In sweet wines, 

 even a somewhat larger amount may be present without causing injury. 



Much larger amounts are injurious in two ways. When the acetic 

 acid is perceptible to the taste, the wine is spoiled. When an abnormal 

 amount of acetic acid is produced before or during fermentation it 

 stops or interferes with the work of the yeast. In such cases, the win^ 

 "sticks," that is, fails to eliminate all its sugar and becomes especially 

 open to the attacks of other bacteria. 



Wines high in alcohol are less liable to acetic fermentation than 

 weaker wines. Sound wines containing over 14 per cent by volume 

 of alcohol are almost immune, but such wines may be spoiled during 

 fermentation by the growth of acetic bacteria on the exposed float- 

 ing "cap" of pomace or on the crushed grapes, especially at high 

 temperatures. 



Anaerobic Organisms {Facultative and Obligate). — Some of the 

 worst, most frequent, and most difficult diseases and defects of wine 

 to treat are due to organisms which develop only in the absence 

 of oxygen. These organisms are all bacteria and appear to include a 

 large number of forms, though, owing to difficulties of isolation and 

 culture, the different forms have not been well studied or described. 



