ON THE ART OF MAKING WINE. 15 



been applied. If the juice of the grape, for ex- 

 ample, be exposed to heat and rest, a coagulable 

 substance is separated. The juice then ceases to 

 ferment with the same facility, but may again be 

 induced to undergo that change, by a re- addition 

 of a matter similar to that which was separated 

 from it. This matter is found in all vegetables, 

 in some, as in wheat, conspicuously ; and it appears 

 to constitute the greater proportion of yeast, as 

 well as of the lees of wine and beer, or other fer- 

 mented fluids. Here, then, we have the theory of 

 this process, as it is applied to artificial com- 

 pounds. It consists of mixing with a solution of 

 pure sugar in water, a certain proportion of this 

 unknown substance, which, to distinguish it from 

 common yeast, I shall hereafter call by the name 

 of leaven. It is on the proportion, quality and 

 management of the leaven, that the most import- 

 ant consequences in vinification depend. I must 

 therefore describe at more length, the various 

 modes under which it appears. 



The natural leaven of fruit, is coagulable, and par- 

 tially separable by heat, but it is not entirely render- 

 ed inert. From this cause, as well as from the partial 

 dissipation of the water and concentration of the 

 sugar, boiled juices produce a sweet wine, the pro- 

 cess of fermentation being rendered incomplete 

 by a partial separation of the leaven. When the 

 process of fermentation is suffered to proceed in 

 of the natural compounds formed in tho 



