TANNIC ACID IN WINE. 191 



acid, and holds the largest amount of colouring matter 

 in solution. The wine is not red, but dark violet, and 

 contains in proportion but a small quantity of free acid. 



Young Port wine, when drawn off into bottles, and 

 clear, deposits without intermission, and during a 

 series of years, a sediment of organic matters which 

 may be loosed from the lower parts of the bottle in 

 complete cakes. 



The more copious the deposit, the clearer will be 

 the colour of the wine. The violet hue which it had 

 when young becomes red, then yellowish red, and at 

 length yellow ; at last the colour agrees so exactly with 

 that of liqueur wine as to make it often difficult to dis- 

 tinguish Port wine by the colour alone from Madeira, 

 and other wines. The alterations which Port wine 

 undergoes are such as are common in a greater or less 

 degree to all other heavily loaded wines, and in all 

 such a deposit is formed, and the colour of the wine 

 rendered lighter, becoming dark yellow instead of red. 

 This colour is well known in strong old cellared Bor- 

 deaux wines. If these wines are left in casks which 

 are kept properly filed, the alteration takes place 

 more quickly than in bottles. 



A great deal of tannic acid is contained in Port and 

 heavily loaded Bordeaux wines. The oxygen of the 

 air which is either dissolved in wine, or present in the 

 bottles or casks, oxidises this tannic acid to a sub- 

 stance which is sparely soluble, and is called by 

 Berzelius apothema, or precipitate of tannic acid. 



