PROCEEDINGS OF THE FARMERS' CIUB. Ill 



THE CHEMISTRY OF WINE MAKING. 



Wine, in its absolute sense, is understood to mean the result of 

 transformations in the constituents of the juice of the grape, by- 

 vinous fermentation. The essential constituents for making wine 

 are sugar, gluten or albumen, free tartaric acid and water; these 

 exist in the juice of the grape, and when the sugar and the acid 

 have been transformed by fermentation, the juice acquires the 

 peculiar properties of wine ; for, in the process of fermentation 

 the sugar has been transformed into alcohol, and the acid into 

 certain substances which give to wine its peculiar taste and 

 smell. 



The proportion of sugar and of acid in the juice varies accord- 

 ing as the grape is grown in a southern or a temperate climate. 

 But the gluten appears to be a constant quantity in whatever 

 climate the grape be grown. In southern climates the juice con- 

 tains more sugar and less acid than the juice of grapes grown in 

 temperate climates ; and the wine, though sweet, has not any odor. 

 The juice of the grape grown in temperate climates has more 

 acid and less sugar, but the perfume is intense ; and hence, as 

 Liebig states, the connection between the acid and the charac- 

 teristic perfumes of the wine, can scarcely be doubted. 



If the oxygen of the atmosphere be completely excluded from 

 grape juice, its constituents will not undergo any perceptible 

 change ; but if it have access to the juice, the oxygen will imme- 

 diately act upon the gluten, and decompose it ; and the gluten, 

 in the act of decomposition, will communicate its state of change 

 to the sugar with which it is in contact, 'and transform it, that 

 is, split up the atoms of sugar into alcohol and carbonic acid, 

 provided the temperature does not exceed 80 or 90 degrees. At 

 higher temperatures, the action of the gluten transforms the sugar 

 into carbonic acid, mannite, lactic acid (acid of sour milk) and 

 gum, instead of alcohol. 



Fermentation, putrefaction and decay are all processes of de- 

 composition, but giving different results. The two princii)a] con- 

 stituents of grape juice on which fermentation depends, are the 

 gluten or albumen, and sugar. Sugar is called a non-nitrogeni- 

 zed substance, and is composed of oxygen, carbon and hydrogen ;, 

 gluten is called a nitrogenized substance from its containing, in 

 addition, nitrogen ; it also contains sulphur. The latter ele- 

 ments, says Liebig, are the true exciters of fermentation, that is, 

 the transformers of non-nitrogenous substances. So long as glu- 



