324 
Book IV. 
Extractive 
matter ne 
cessary. 
Orgen ab 
sorbed. 
A certain 
tain tempe 
rature re 
quired. 
RRechs ol 
the fermen 
tation. 
FERMENTED SUBSTANCES. 
ment, is decomposed during the process, and contri 
butes to the formation of the acetous acid. 
2. Wine entirely deprived of extractive matter, either 
by spontaneous deposition or by clarification, does not 
undergo the acetous fermentation, unless some mucila 
ginous matter be mixed with it. Chaptal exposed old 
wine destitute of this matter, in open bottles, to the 
greatest summer heat of Montpelier for 40 days, and 
yet it did not beconte sour : But upon adding some 
vine leaves to the same wine, it became acid in a few 
days *. 
3. Wine never becomes sour, provided it be com 
pletely deprived of all access to atmospheric air. The 
reason is, that during the acetous fermentation, oxygen 
is absorbed from the atmosphere in abundance; and un 
less that absorption can take place, no vinegar is ever 
formed. Hence the reason that wine or beer is more 
apt to become sour after the cork has been drawn, and 
still more apt when part has been poured out of the 
bottle. 
4. A pretty high temperature is necessary for the 
commencement of the acetous fermentation. Wine or 
beer (unless very weak) scarcely become sour under the 
temperature of 65° or 70°. The fermentation is very 
apt to commence when the temperature suddenly rises. 
It is said, too, that wine and beer are more apt to be 
come sour at certain seasons of the year than at others. 
5. When the acetous acid is completed, the whole of i 
the malic acid originally contained in the wine has dis 
appeared as well as the alcohol. We must conclude, 
therefore, that they have been both converted into ace 
X Ann. de Chim. XXXvi. 245.