313 VINOUS FERMENTATION. 



remains mixed with the wine in an undecomposed state, the con- 

 dition necessary for its further decomposition being absent. 



The azotized matters in the juice of grapes of the temperate 

 zones, on the contrary, are not completely separated in the 

 insoluble state, when the entire transformation of the sugar is 

 effected. The wine of these grapes, therefore, does not contain 

 sugar, but variable quantities of undecomposed gluten in solu- 

 tion. 



This gluten gives the wine the property of becoming spon- 

 taneously converted into vinegar, when the access of air is not 

 prevented. For it absorbs oxygen and becomes insoluble ; and 

 its oxidation is communicated to the alcohol, which is converted 

 into acetic acid. 



By allowing the wine to remain at rest in casks with a very 

 limited access of air, and at the lowest possible temperature, the 

 oxidation of this azotized matter is effected without the alcohol 

 undergoing the same change, a higher temperature being neces- 

 sary to enable alcohol to combine with oxygen. As long as the 

 wine in the stil ling-casks deposits yeast, it can still be caused to 

 ferment by the addition of sugar, but old well-cleared wine has 

 lost this property, because the condition necessary for fermenta- 

 tion, namely, a substance in the act of decomposition or putre- 

 faction, is no longer present in it. 



In hotels and other places where wine containing much gluten 

 is drawn gradually from a' cask, and a proportional quantity of 

 air necessarily introduced, its eremacausis, that is, its conversion 

 into acetic acid, is prevented by the addition of a small quantity 

 of sulphurous acid. This acid, by entering into combination with 

 the oxygen of the air contained in the cask, or dissolved in the 

 wine, prevents the oxidation of the organic matter. 



The various kinds of beer differ from one another in the same 

 way as the wines. 



English, French, and most of the German beers, are converted 

 into vinegar when exposed to the action of air. But this pro- 

 perty is not possessed by Bavarian beer, which may be kept in 

 vessels only half-filled without acidifying or experiencing any 

 change. This valuable quality is obtained for it by a peculiar 

 management of the fermentation of the wort. The perfection of 



