THE MANUFACTURE OF VINEGAR 541 



alcohol, the bacteria develop readily and produce in suitable solutions, 

 besides acetic acid, agreeable ethers which are more abundant when 

 the oxidation is slow. Below i or 2 per cent of alcohol, the bacteria 

 attack these ethers, and finally the acetic acid itself, causing complete 

 oxidation according to the equation: 



C2H4O2 + 40 = 2CO2 + 2H2O. 



The addition of a new supply of alcohol, however, immediately 

 arrests this reaction. In practice the acetification should be stopped 

 when the alcohol has fallen to i or 2 per cent, otherwise there is a loss 

 of flavor and of acetic acid, which may continue until all the acid is 

 destroyed. 



The length of time during which the acetic bacteria retain their 

 vitality varies with the moisture and the temperature. In nutrient 

 solutions, they Hve from one to as many as ten years; in the dry state, 

 from three months at ordinary temperatures, to twelve months at 2°. 



Processes or Manufacture 



Raw Materials. — Originally vinegar was made from wine, as 

 indicated by the etymology of the word which means "acetified wine." 

 Later, other alcoholic beverages such as cider and beer were used for 

 the same purpose. In these liquids, the acetic bacteria find all the 

 mineral and organic matters necessary for their development, together 

 with alcohol in amounts favorable for acetic fermentation. At present, 

 a large number of materials containing alcohol, or starchy and sugary 

 matters, which, by prehminary yeast fermentation, can be changed 

 into alcohol are used as sources of vinegar. The most important of 

 these are honey, malt, and various fruit juices. 



All these materials make wholesome vinegar of varying degrees of 

 quaUty. Those of wine and cider are usually classed as the best, and 

 those of' malt and honey next. The great bulk of the vinegar of com- 

 merce, however, at present is made by the acetification of distilled 

 grain, potato and molasses alcohol. This is not vinegar strictly speak- 

 ing but an imitation, consisting of a dilute solution of acetit acid with- 

 out the various flavors which are an essential part of pure vinegar. In 

 order to give it a semblance of the latter, it is often colored with 

 caramel and flavored with various substances. 



