92 FERMENTATION. 



In red wine a portion of colouring matter and of 

 tannic acid is withdrawn by these salts, which is thus 

 rendered less astringent and of a lighter colour. 



The tannic acid is precipitated with other sub- 

 stances which were held in solution, and in order to 

 prevent them from being brought within the range 

 of decomposition (which happens when the admis- 

 sion of air changes the tannic acid into apothema, 

 and sets free the albumen, whereby a new spring of 

 chemical action, often injurious to the wine, is set 

 free) the wine during after-fermentation is several 

 times transferred into other casks, and so freed from 

 sediment. The transfer into fresh casks must be re- 

 peated so long as deposit of raw tartar forms; the 

 wine cannot be bottled until this ceases. 



In these respects the wine differs from the grape 

 juice out of which it is prepared. 



When the skins are allowed to ferment, a diminu- 

 tion of some and an admission of other constituents 

 takes place. In the first place, the water of the wine 

 may dissolve some substances from the crushed grape 

 skins, for example, tannic acid. If the action of the 

 water be assisted by alcohol, the solution will be 

 stronger, and colouring matter extracted from the 

 skins will also be dissolved with the tannic acid, and 

 that in proportion to the quantity of alcohol formed 

 out of the sugar. 



In the manufacture of the best Burgundy and 

 coloured Champagne the skins remain in the liquid 



