COLOURING MATTERS IN WINE. 203 



mentation, apothema will form in it very quickly, 

 and the colour of the wine becomes actually brown. 

 Boiled wines (so called on account of the evaporation 

 they undergo), such as Malaga, Tinto, &c., without 

 possessing any peculiar colouring matter, are thus 

 rendered brown, and their colour will be dark in 

 proportion to the heat to which they were exposed, or 

 the length of time during which they were in contact 

 with the air. Evaporated grape juice leaves as resi- 

 due a dark brown substance. But even wine that 

 is almost colourless yields, when allowed to evaporate 

 in the air upon a water bath, a dark brown extract, 

 the colour of which must be attributed to the above- 

 mentioned causes. 



Every so-called apothema is a humic acid, and 

 frequently bears traces of the substance from 

 which it originates ; hence the slight differences in 

 their qualities. We talk, therefore, of the apothema 

 of extractive matter, apothema of tannic acid, &c. 

 What kind of humic acid it may be is not yet deter- 

 mined, perhaps it is apocrenic acid. 



Wines prepared from white grapes, in which the 

 skins have been allowed to ferment, are much yel- 

 lower, sometimes, indeed, dark yellow; these are 

 known as liqueur wines. Whilst the juice of these 

 grapes ferments, the wine, which is in process of 

 formation, extracts tannic acid from the skins of 

 the white grapes, and holds it in solution. 



Such a wine must in course of time acquire more 



