WINES. 321 



7. Water, 70 to 90 per cent. 



The must is fermented in suitable vats of wood or stone, according to 

 tbe usage of the country; the fermentation is produced spontaneously, 

 that is, by germs accidentally introduced iuto it from the air or on the 

 surface of the grapes themselves. If the fermentation does not take 

 place promptly it is started up by introducing into it a supply of yeast- 

 cells from some must which is already in a state of fermentation. Some- 

 times a small quantity of must is fermented in anticipation of the vint- 

 age season as a " sponge," its fermentation being first induced by a 

 small quantity of well washed beer yeast. The use of albuminous 

 yeasts, such as bread yeast, &c., is generally avoided as much as possi- 

 ble, however, as tending to produce lactic and acetic or other objection- 

 able fermentations entirely incompatible with the production of a wine 

 with a delicate flavor. 



The temperature at which the fermentation is carried on has a very 

 decided influence upon the character of its product, and the practice 

 diifers in different countries in this respect. In California, Spain, South 

 of France, Austria, and Hungary fermentation is conducted at a com- 

 paratively high temperature, 15 to 20 C., while in Germany a low tem- 

 perature, 5 to 3 5 C., is employed. As with beer, the yeast of either 

 variety of fermentation, high or low, reproduces the same kind of fer- 

 mentation in umsts to which it is added, but the subject of the different 

 ferments, as applied to wine, has not been so carefully studied as with 

 beer. The high fermentation is said to give a wine rich in alconol, but 

 lacking.in bouquet, while the reverse is the case with the low fermenta- 

 tion. 



The duration of the fermentation varies with the temperature, the 

 amount of sugar to be transformed, &c. ; the completion of the process 

 may be l r nowu by the cessation of the disengagement of carbonic acid 

 gas and by the diminution of the specific gravity of the liquid, so that 

 the areometer marks zero or less. 



After fermentation is complete, the wine is drawn off from any sedi- 

 ment it may contain into casks or barrels, where a second slow ferment- 

 ation takes place, continuing sometimes several months. When it is 

 over, the wine is "racked off' 7 into fresh casks, which are closely bunged 

 up. The operation of racking off may have to be repeated several 

 times, and it is sometimes necessary to add isinglass, or other gelatinous 

 material, which serves to clarify the liquid, acting on the tannin which 

 it contains. This operation is called "fining." 



CHANGES PRODUCED BY FERMENTATION. 



The principal change in the chemical constitution of the must pro- 

 duced by fermentation is the conversion of the sugar into alcohol and 

 carbonic acid. One hundred parts of sugar produce 50 parts of alcohol, 

 in round numbers. All the sugar, however, is not converted into alcohol 

 and carbonic acid ; a small part is converted into glycerine and succinic 

 acid. 



