212 COLOURING MATTERS IN WINE. 



tion or analysis of them. This wine must, therefore, 

 be red, even if it be prepared without the skins being 

 permitted to ferment. 



What we call red wine, is wine prepared from 

 either black, purple, or red grapes, the juice of which 

 is colourless, and the skins of which are allowed to 

 ferment. During fermentation the weak spirit which 

 is formed extracts not only tannic acid, but blue 

 colouring matter from the skins. This blue colouring 

 matter is tinged more or less red by the tartaric acid 

 of the wine, and may afterwards be rendered more 

 decidedly red by the formation of acetic acid. In 

 the change of colour undergone by red wine five 

 periods must be distinguished. As soon as alcoholic 

 liquid is formed during fermentation, blue colouring 

 matter begins to be extracted from the skins. As the 

 small amount of blue colouring matter is brought 

 into contact with grape juice, which has an acid re- 

 action, it becomes red. The fermentation and forma- 

 tion of alcohol proceed, as does also the solution of the 

 blue colouring matter ; hence there is seldom sufficient 

 tartaric acid to redden the blue colouring matter, and 

 the young wine is rather blue than red, and may be 

 called dark violet. This, new wine now undergoes after 

 fermentation (p. 91), during which a great deal of 

 colouring matter and red tartar, as well as albumen 

 and apothema of tannic acid, is precipitated. The loss 

 of the colouring matter causes the wine to become 

 lighter. In the meantime the formation of acetic acid 



