420 
transformed into sugar; a small amount of acids and albuminoid 
substances are also met with there. 
Layer e, which underlines the pellicle, contains the colouring 
matter, also tannie acid, and some aromatic substances which im- 
part a peculiar flavour to certain grapes, such as the Muscats, 
Riesling, Cabernet, Isabella, and other American grapes. These 
natural aromas are quite distinct from those ethers which consti- 
tute the bouquet of matured wines, and which are the result of 
chemical reactions between the acids and the alcohol in the wine. 
The colouring matter, or onocyanine, although generally lining the 
skin of grapes,.is occasionally found in the pulp of some varieties. 
There are two distinct sorts—a yellow and a blue one—--which, when 
in contact with the acids in the wine, turn red. 
As grapes ripen, there is a gradual migration of the sugar 
from the centre towards the circumference, where it accumulates 
under the skin. This explains why, when pressing grapes which 
are dead-ripe, the juices which run out first are not so sweet as 
those which flow when greater and more prolonged pressure has 
been applied. 
The following table gives the composition of fresh grape must 
and of the resulting fermented wine:— 
Must. Wine. 
% % 
Water vite es 73-86 Water 
Albuminoid matters oi Residues of albuminoid 
matters 
Glucose chiefly bees 
Alcohol ... oes 6-14 
Glucose (chiefly dextrose) 12-24 eee qo Goa ee 
Renee acid 
Ethers 
Gum Gum 
Vegetable mucus 
Colouring matters (traces Colouring matters 
only) 
Tannin (traces) Tannin 
Malice acid (in bad seasons) Malic acid in (bad seasons) 
Tartaric acid 
Potassium hydrogen tar- Potassium hydrogen tar- 
trate 
trate 
Calcium tartrate Calcium tartrate 
Other salts of organic Other salts of organic 
matters matters 
Mineral matters ... Mineral matters 
Sp. gr. oe ie ..- 1065-1107 | Sp. gr ints we *991--996 
Total dry residue ve, 14-27 Total. residue... one 1-3% 
