164 GRAPES. 



matter present will not enter into an active state of 

 decomposition, unless free oxygen has access to it. 

 Consequently whole grapes, or those in which the 

 skin remains perfect and entire, may be dried and 

 converted into raisins; but if the skin is once injured, 

 a little air gets in, and fermentation soon commences. 

 The fermentation of grape juice will not take place 

 if the grapes are pressed in a jar containing carbonic 

 acid gas, or nitrogen. 



383. When grapes are pressed, which is the first 

 process of the wine-maker, they are generally bruised, 

 and then allowed to remain some little time in the 

 pressing- vat, before the operation is completed. This 

 allows fermentation to commence, for it begins as 

 soon as the juice comes in contact with the air; and 

 this fermentation, besides softening the skins and 

 cellular tissues of the grapes, also dissolves a portion 

 of the coloring and astringent matter which the skins, 

 seeds, and stalks contain. The pressing is then com- 

 pleted, and the juice separated from the residue, 

 which is termed the murk, or the mark. 



384. A certain degree of warmth is always neces- 

 sary to fermentation. The fermenting liquid must 

 not be lower than 51° or higher than 85°. A tem- 

 perature of 70° is that most favorable to rapid fer- 

 mentation. When the liquid is cooled, its ferment- 

 ation suffers a proportionate check, and if cooled too 

 much, it ceases altogether. When this is the case, 

 it can only be brought on again by the careful appli- 

 cation of heat. 



