THE ALCOHOLIC FERMENTATION. 213 
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 fermentation, 
since the wild yeasts are sufficient to give all the inoculation neces- 
sary. In the making of wines the usual method is simply to press 
out the juice from the grape and then to allow a spontaneous fermen- 
tation 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 revolu- 
tion 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, certainly suggests 
that, in wine-making, an improvement may be anticipated 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 im- 
proved 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 subsequently 
kept from further contamination by being bottled. The principle 
concerned is simple, but there are various practical difficulties in the 
way that make it difficult to produce a good quality of grape 
juice. 
The term wine usually refers to the fermented juice of the 
grape. But in sections of the country where grapes are not exten- 
sively grown other fruit juices are used. Wines are made from the 
juice of blackberries, currants, raspberries, elder berries, etc. In the 
making of wine from these fruits, since the juice is not very sweet, 
sugar is commonly added in amounts varying with the sweetness of 
the fruit and depending also on whether a sweet or sour wine is 
desired. The mixture is then generally left to ferment spontaneously 
under the influence of the wild yeasts that are abundant enough to 
