TREATMENT OF FRESHLY-PREPARED VINEGAR. 147 



ment to continue to exist upon the surface and to slowly convert 

 the small quantity of alcohol still present into acetic -acid. 



If the barrels are not closed absolutely air-tight, the vinegar 

 ferment will develop quite vigorously upon the surface, and when 

 all the alcohol is consumed attack the acetic acid, so that when 

 the vinegar is tested a decrease in the content of acetic acid is 

 plainly perceptible. If the finished vinegar still contains consid- 

 erable quantities of albuminous substances in solution (vinegar 

 from grain, malt, or fruit), or if it contains tartaric and malic acids 

 and at the same time only a small percentage of acetic acid, as 

 most fruit vinegars do (seldom more than 5 per cent.), the mold 

 ferment readily settles upon the vinegar and finally dislodges the 

 vinegar ferment from the surface. The acetic acid is, however, 

 very rapidly destroyed by the mold ferment, and through a luxu- 

 riant growth of the latter, which floats upon the surface as a 

 white, membranous coating, the vinegar may in a few weeks lose 

 one or more per cent, of it. This happens so frequently, for in- 

 stance with fruit-vinegar, that the opinion that such vinegar cannot 

 be made to keep, is quite general. 



Vinegar which, besides a considerable quantity of extractive 

 substances, contains the salts of certain organic acids (malic and 

 tartaric acids), for instance, vinegar prepared from apples or 

 wine, must be frequently examined, as it readily spoils and may 

 suffer even if kept in barrels constantly filled up to the bung. 

 In fluids containing the salts of the above-mentioned organic 

 acids a ferment may frequently develop, even when the air is ex- 

 cluded, which first decomposes the" tartaric and malic acids, and 

 though these acids are present only in a comparatively small 

 quantity, they influence, to a considerable extent, the flavor of the 

 vinegar on account of their agreeable acid taste. In vinegar in 

 which this ferment has long existed a diminution of acidity can 

 be readily detected by the taste, and by the direct determination 

 of the acid a decrease in its content can be shown which, if cal- 

 culated as acetic acid, may in some cases amount to one per cent. 

 Besides the loss of its former agreeable taste vinegar thus 

 changed acquires a harsh tang, due no doubt to the formation of 

 certain not yet known products formed by the ferment effecting 

 the destruction of the tartaric and malic acids. Moreover, wine 



