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 



