THE GEAPE. 41 



two points to be considered with respect to grape- 

 skins, the tannic acid which is found both in purple 

 and white skins, and the colouring matter, which is 

 only met with in the skins of the purple grapes. 



Not the slightest trace of tannic acid is to be 

 found in the juice of either kind of grape. When 

 tannic acid is discovered in white wine, it proceeds 

 from the skins, a larger or smaller quantity of which 

 were included 'in the fermentation. And the same 

 holds good with regard to red wine; for no more 

 tannic acid can be detected in the juice of the purple 

 than in that of the white grape. 



Any one may convince himself both of the ex- 

 istence of tannic acid in the skins, and of the presence 

 of a larger quantity of acid in the purple than in the 

 white skins, by boiling them with water, and adding 

 gelatine, or salt of oxide of iron. The larger the 

 quantity of skins, and the more they are pressed in 

 preparing wine, the greater will be the quantity of 

 tannie acid in the wine. Tannic acid is soluble in 

 alcohol and water. 



The juice of white grapes allowed to ferment with- 

 out the skins yields a wine almost entirely free from 

 tannic acid. "Wines prepared in this manner lose less 

 of their colour by age than any others. White grape 

 juice, on the contrary, in which the skins are allowed 

 to ferment, gives a liqueur-wine which darkens with 

 age. 



We shall speak more particularly of this circum- 



