542 MICROBIOLOGY OF SPECIAL INDUSTRIES 



Other imitations of vinegar sometimes appear on the market, con- 

 taining wood vinegar, or even mineral acids. These, however, are more 

 or less poisonous and their sale, as food, is usually forbidden by law. 



Fermentation. — If the raw material to be used is starchy ' or 

 sugary, it must be first changed into an alcoholic hquid containing from 

 6 to 12 per cent of alcohol by volume. This is accomplished by one 

 of the methods discussed in the preceding chapter. This alcohoHc 

 fermentation must be kept rigidly distinct from the acetification and is 

 best carried out in a separate building. The yeast must finish its work 

 before the bacteria commence theirs. The reason for, this is that 

 yeasts are very sensitive to acetic acid and a small quantity may 

 paralyze their activity and prevent the change of all the sugar into 

 alcohol, with a consequent loss of strength and quality in the final 

 product. 



The quaUty of the vinegar will depend on the quality of the raw 

 material from which it is made. Wine or cider spoiled by bacterial 

 fermentation, moldy casks, etc., will make inferior vinegar. An 

 exception to this may be made of so-called "pricked" wines, which are 

 simply wines in which acetic fermentation has started spontaneously. 

 The wine or other alcoholic liquid should be perfectly clear and clean 

 tasting and, if necessary, should be fined, filtered or pasteurized im- 

 mediately before use. It should contain no antiseptic which would 

 interfere with the development of the acetic bacteria. Sulphurous 

 acid, if present in the free state, should be removed or oxidized by 

 thorough aeration. 



Commerical alcohols made from corn, potatoes, beets, molasses and 

 other products can be used. The special flavors of these alcohols, due 

 to their origin, disappear almost completely in the vinegar. This, 

 however, is not true of denatured alcohol or that containing methyl 

 alcohol or acetone. 



The alcohol must be diluted to from lo to 1 2 per cent by volume, and 

 then made suitable for the growth of acetic bacteria by the addition of 

 nutritive substances containing nitrogen and phosphates. This is ac- 

 complished usually by adding lo per cent of wine, beer, malt-extract, 

 yeast decoction, or similar material to the diluted alcohol. The waste 

 liquids from a brandy distillery may be usedinsteadof water for dilution. 

 After resting a few days, the mixture is filtered and is then ready for 

 acetification. 



