172 TRANSACTIONS OF THK AMERICAN INSTITUTE, 



ten, in a continuing state of decomposition exists side by side 

 with sugar in a fluid, fermentation proceeds. While oxygen is 

 excluded, both these processes of transformation, namely, that of 

 the gluten and that of the sugar, complete themselves side by 

 side, and mutually limit each other ; so that if the transforma- 

 - tion of the sugar into alcohol be completed before that of the 

 gluten, as happens in grape juice poor in sugar, a certain portion 

 of the gluten or ferment, as it is called, remains undecomposed, 

 ■without undergoing further alteration, so long as the access of 

 oxygen is thoroughly precluded. If fresh sugar be added to the 

 juice, it possesses the property of again passing into a state of 

 fermentation, and if the transformation of the gluten is completed 

 before that of the sugar, the still undecomposed sugar remains 

 unaltered, as in the wines of southern countries, which are gen- 

 erally sweet. 



But if oxygen have access to the wine, as it will have, even in 

 a closely bunged cask, through the pores of the wood, then, if 

 there remain in the Avine any undecomposed gluten after all the 

 sugar is transformed into alcohol, the presence of the decompos- 

 ing gluten transmits its action to the particles of alcohol, and 

 transforms the alcohol into acetic acid ; the wine becoming sour, 

 that is, converted into vinegar. 



If, however, the fermentation or decomposition of the gluten 

 be carried on in wide, open, and shallow vessels, at a tempera- 

 ture not higher than fifty degrees, the gluten will be decomposed 

 and separated from the wine by precipitation ; and the wine may 

 afterwards be exposeji to the air at any temperature, for any 

 length of time, without becoming acid. 



It may now, says Liebig, be easily understood that we can 

 exercise a decided influence on the juice of the grape. We may 

 rationally improve a must (juice) in Avhich the gluten is in ex- 

 cess, by the addition of sugar ; and it is a matter of perfect 

 indifference that this sugar has been produced from the organism 

 of some other species of plant, and added to the juice of iinripe 

 grapes. In a scientific point of view these are real improve- 

 ments, which have nothing in them very recondite, very difficult 

 of comprehension, or objectionable. 



The application of this knowledge respecting the phenomena 

 attendant upon fermentation and decay is obvious and easy. We 

 see that the conversion of wine into vinegar, when the wine is in 

 contact with air, depends on the gluten undergoing decomposi- 



