648 MICROBIOLOGY OF ALCOHOLIC FERMENTATION 



the vinegar. Frequent and thorough cleaning of all apparatus, pasteur- 

 ization of liquids and light sulphuring of empty casks will prevent its 

 development. The vinegar eels are easily killed by heating the vinegar 

 to 50. They may be removed by nitration or fining. 



Microscopic mites are sometimes troublesome in neglected factories. 

 They can be reduced by the methods recommended for vinegar eels 

 and their entrance into the barrels or acetifying columns prevented by 

 painting a ring of turpentine or some viscid substance around each air 

 hole. 



Vinegar flies (Drosophylla cellaris) are often troublesome, but can be 

 excluded by proper screening of buildings and barrels. 



Bacteria other than acetic may develop in vinegar and some of 

 them may depreciate its quality. These have been little studied but 

 the most harmful seem to be anaerobic forms which develop in the 

 lower parts of the liquid protected from oxygen by the screening film 

 of the acetic bacteria. They produce butyric acid and putrid odors 

 and, if neglected, may completely spoil the vinegar. Sulphuring, fining, 

 and pasteurization are the remedies. 



Darkening or persistent cloudiness may be caused by oxidase as in 

 wine and cider and is controlled in the same way. A similar defect may 

 be caused by the tannic extractive matters of new casks or contact with 

 iron. Aeration followed by fining will remove the cause of the trouble. 



