ON THE FEEMENTATION OE JUICE. 49 



evaporated, and the juice, being more concentrated, 

 yields a stronger wine. This is the method of prepa- 

 ration which the ancients made use of in order to pro- 

 cure heavy wines, rich in alcoholic contents. They 

 evaporated the fresh grape juice by exposure to mode- 

 rate heat, and the juice afterwards yielded a stronger 

 wine. When the grapes are allowed to dry on 'the 

 vine, the wine is called vin sec (dry wine) ; when they 

 are dried on straw, vin de paille, grapes ; and when the 

 juice has been evaporated by means of heat, vin cotti, 

 or boiled wine. 



We have already seen (p. 32) that the saccharine 

 contents of the grapes amount to from 13 to 30 per 

 cent, of the juice. 



If we reckon all this as grape-sugar, and in a 

 hydrated state = C 13 H 14 O 14 equivalent = 198, then 

 as alcohol is C 4 H 6 O 3 , and therefore equivalent = 46, 

 and two equivalents alcohol are formed from one 

 equivalent grape sugar, then 198 parts grape sugar 

 would give, supposing there to be no loss, and all 

 the grape sugar to be converted into alcohol, 92 parts 

 of alcohol. 



198 grape sugar gives 92 alcohol, but for the sake 

 of brevity we shall consider them as 2 and 1. 



According to this the juice of Prench and Grerman 

 grapes gives, when analysed, as a maximum, from 

 7 to 15 per cent, of alcohol by weight. 



But some of the sugar remains undissolved, and 

 during fermentation more alcohol is evaporated than 



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