THE MANUFACTURE OF VINEGAR 647 



beech chips and half filled with the liquid to be acetified. By rotating 

 the barrel at short intervals the liquid trickles repeatedly over the chips 

 and, with proper aeration, the acetification is rapid and complete. The 

 same principle has been applied successfully by means of "drums" 10 

 feet long by 4 feet in diameter partially immersed and rotating in 

 the liquid of a closed vat to which air is admitted by adjustable holes. 



FUNCTION OF THE FILM. All these methods are based on the suppo- 

 sition that the formation of acetic acid depends on the work of the bac- 

 terial film at the surface of the alcoholic liquid. It seems probable 

 that the only function of the film is to maintain the bacteria in a posi- 

 tion where they can obtain a full supply of oxygen. If this is true, 

 oxygen supplied by a stream of compressed air or other efficient means 

 of aeration should be equally effective even in the absence of a film. 



An observation by W. V. Cruess indicates that the film formation 

 may actually hamper the work of the bacteria. This observation is 

 that certain forms of vinegar bacteria which do not form films produce 

 acetic acid very rapidly. The observation was made on wine in small 

 flasks and at temperatures of 2o-33. Whether the formation of 

 acetic acid would be equally rapid in larger volumes of liquid where the 

 penetration of oxygen would be slower has not been determined. 



AFTER-TREATMENT. Alcohol vinegars require little treatment. 

 They should be filtered and are usually colored slightly with caramel. 

 Being little more than dilute solutions of acetic acid without ethers or 

 bouquet, there is no object in aging them. 



Wine and cider vinegars, for the best results, require aging and 

 careful treatment. They should be filtered and pasteurized as soon as 

 made and stored in clean casks which are well bunged and kept con- 

 stantly full in a cool place of even temperature. If too dark in color, 

 they may be decolorized with pure animal charcoal carefully extracted 

 with acids and water. 



Before using or bottling, the vinegar should be fined with isinglass 

 (see page 620). 



DISEASES 



The most troublesome pest of vinegar factories is a minute nema- 

 tode, the Anguillula aceti or vinegar eel. It often develops around the 

 edges of the surface of the liquid in vinegar barrels and in the acetify- 

 ing columns and, if neglected, may cause putrefaction and spoiling of 



