VARIOUS PROPERTIES OF WINES. 293 



yeast formed during fermentation in the south of 

 France, and on the Rhine. 



The grapes grown in hot climates, as well as the 

 boiled juice obtained from them, are proportionally 

 rich in sugar. Hence, during the fermentation of 

 the juice, the complete decomposition of its azo- 

 tised matters, and their separation in the insoluble 

 state, are effected before all the sugar has been 

 converted into alcohol and carbonic acid. A cer- 

 tain quantity of the sugar consequently remains 

 mixed with the wine in an m undecomposed state, 

 the condition necessary for its further decomposi- 

 tion being absent. 



The azotised matters in the juice of grapes of 

 the temperate zones, on the contrary, are not com- 

 pletely separated in the insoluble state, when the 

 entire transformation of the sugar is effected. The 

 wine of these grapes, therefore, does not contain 

 sugar, but variable quantities of undecomposed 

 gluten in solution. 



This gluten gives the wine the property of 

 becoming spontaneously converted into vinegar, 

 when the access of air is not prevented. For it 

 absorbs oxygen and becomes insoluble ; and its 

 oxidation is communicated to the alcohol, which is 

 converted into acetic acid. 



By allowing the wine to remain at rest in casks 

 with a very limited access of air, and at the lowest 

 possible temperature, the oxidation of this azotised 



