FERMENTATION. 73 



palp of grapes, and should these be brought into 

 a state of transformation, by contact with air, they 

 not only ferment, but excite the formation of alcohol 

 and carbonic acid from the sugar. But gum and 

 sugar are also found in grape juice, and fermen- 

 tation may therefore be induced in it. And if 

 ferment be once formed it may be decomposed at 

 a later period, and fermentation kept up. No fer- 

 ment can be detected in grape juice, but it is found 

 after fermentation. The formation dates from the 

 commencement of fermentation, and continues several 

 days ; its decomposition extends over a period of 

 months, for this latter process does not consist merely 

 in the emptying of the yeast cells, nor is this, indeed, 

 its principal characteristic. The decomposition of 

 yeast depends principally upon the chemical change 

 of the albuminous matter which was formerly con- 

 tained in the yeast cells. 



The active fermentation of grape juice, which 

 attains its highest point in 10, 12, or 14 days, is the 

 period during which the decomposition of vegetable 

 albumen and mucus, the formation of ferment and the 

 emptying of ferment cells takes place ; that is, the 

 exudation of the albuminous contents through the 

 walls of the cells. The after-fermentation is the 

 period during which these albuminous contents de- 

 compose. During the after-fermentation a great deal 

 of sediment is formed from the wine, but this contains 

 no ferment. What this sediment is, we shall mention 



