THE ALCOHOLIC FERMENTATION 229 
is also the foundation of the gigantic distillery and brewery indus- 
tries, which make use of grains and other farm products. But 
these hardly belong to our immediate subject. There are, how- 
ever, a few forms of fruit-juice fermentations more or less common 
on our farms. 
Wines.—The name wine is given to the fermented juice of 
fruits. The most common fruit used for this is the grape, whose 
juice is rich in sugar and easily pressed from a mass of the fruit, as 
a clear liquid Upon the skin of the grape there are sure to collect, 
during its growth, a variety of microorganisms, mostly from the 
air, and among them will be enough yeasts to start a fermentation 
of the sugars as soon as the juice is extracted from the grape The 
grape Juice, therefore, needs no yeast added to it to start a fermen- 
tation, since the wild yeasts are sufficient to give all the inoculation 
necessary. In the making of wines the usual method is simply to 
press out the juice from the grape and then to allow a spontaneous 
fermentation to occur Occasionally the practice of adding yeast 
to the juices, in order to hasten or control the fermentation, has 
been recommended. This method, which has made a complete 
revolution in the brewery industries, has not, as yet, been very 
extensively applied to wine-making The knowledge that there 
are many kinds of yeasts with different values in fermenting, cer- 
tainly suggests that, in wine-making, an improvement may be an- 
ticipated by this use of pure cultures The use of pure cultures in 
wine-making is becoming more common, and where they have 
been used an improved product or a better control has been 
claimed. 
Some farms, where grapes are raised in abundance, prepare for 
market an unfermented grape juice which is essentially wine that 
has not been allowed to ferment. The expressed juice is sterilized 
by a temperature of about 170°, which is sufficient to destroy 
the yeast cells and to prevent fermentation, if the juice be subse- 
quently kept from further contamination by being bottled. The 
principle concerned is simple, but there are various practical diff- 
