WHAT IS WINE? 
355 
greater part of the skins and seeds ; and this expressed juice is 
called must. When white wine is to be made this juice only 
is taken. In the preparation of red wines, however, the skins 
and seeds are allowed to remain in the juice for from 3 to 20 
days before pressing; since the juice even of red grapes would 
otherwise yield a white wine, the colour being imparted to the 
wine by the skins.* 
The must is now put into large vats or casks, and there left. 
Soon it becomes turbid and evolves carbonic acid ; and at the 
same time the growth of a peculiar kind of fungus, the yeast 
plant, may be observed in it. The must has begun to ferment. 
In order to start the fermentation the access of air to the juice 
is essential ; but fermentation, once set up, goes on even if 
atmospheric air be entirely excluded. Most probably the air 
acts merely as a carrier of the spores of the fungus, which 
spores, finding the conditions necessary for their growth in the 
must^ begin to germinate when brought in contact with it. The 
development of the yeast plant requires the presence of a 
nitrogenous as well as of a non-nitrogenous substance, the first 
of which is supplied by the vegetable albumen, the second by 
the sugar. During the growth of this fungus the albuminous 
substance becomes absorbed, and is made insoluble, while the 
sugar is in great part resolved into alcohol and carbonic acid. 
Fermentation then is probably nothing more than a vital 
process of the above-named fungus, by virtue of which it 
absorbs the sugar, converts part of it into cellulose, constituting 
the cellular membrane, and breaks up the rest chiefly into 
alcohol and carbonic acid, both of which substances are excreted 
again by the plant. 
Fermentable sugar is a compound, the molecule of which 
consists of 6 atoms of carbon, 12 atoms of hydrogen, and 6 
atoms of oxygen. During fermentation this compound mole- 
cule of sugar breaks up into 2 molecules of carbonic acid, each 
made up of 1 atom of carbon and 2 of oxygen, and 2 molecules 
of alcohol, each made up of 2 atoms of carbon, 6 atoms of 
hydrogen, and 1 of oxygen ; or, in symbolic language, 
CgIIj20g breaks up into 
twice C 0, = Cg O4 
„ C2HgO = C^2 
CgHigOg 
where C stands for 1 atom of carbon, H for 1 atom of hydrogen, 
and 0 for 1 atom of oxygen : the figure below to the right 
, * Except perhaps the dyer grape teinturier, which, like black currant, has 
a coloured juice. 
