224 Observations on Fermentation. 



sugar a small quantity of oxygen, whereby it becomes a 

 substance sui generis, whose principles not being able to 

 remain in their present arrangement, react upon each other, 

 combine in a new and different order, producing alcohol 

 dissolved in water, and more carbonic acid gas ; the fer- 

 ment which caused these phrenomena is itself altered in 

 part, and precipitated; while the water only serves to bring 

 the molecules into contact, and to retain the alcohol. 



The methods in use for subjecting different substances 

 to the vinous fermentation, may, according to M. Chaplal, 

 be reduced to two ; decoction and expression. The first is 

 practised by means of water in the fermentation of the fa- 

 rinaceous grains, in making beer ; the second is employed 

 in fermentation of juices which afford the different sorts of 

 wine. The details furnished by the author on the prepara- 

 tion of beer being borrowed from Thomson, 1 shall not 

 notice then), especially as T have a great number of facts 

 to relate on the art of making wine. 



On the vinous Fermentation of the Juice of the Grape. 



The sugar and the ferment existing isolated in the grape, 

 it becomes necessary to press this fruit to obtain from it the 

 juice called must, in which these two vegetable principles 

 are mixed together. This jnust speedily ferments at the 

 temperature of 12^ of Reaumur*. M. Chaptal says it is 

 necessary to fill the vat all at once, in order to avoid the suc- 

 cessive fermentations that take place when the must is put 

 in at various times, as this circumstance renders the wine of 

 a bad qualitv. 



This may be the case indeed in countries to the north, 

 where the grapes being very watery, and but little sweet, 

 cannot support any derangement in the fermentation ; but 

 in these southern climates this phasnomenon seldom shows 

 itself. It must necessarily require many days to fill a vat 

 which contains 50 muids, and yet, however, the wine is very 

 excellent which is made in this enormously Urge vessel. 



Before the miist is put into the vat, this latter ought to 

 he cleaned with the greatest care; then the liquor is to be 

 left to ferment in it. According to M. Chaptal, the vinous 

 fermentation is influenced by a variety of circumstances, 

 into which I am successively to inquire. 



1 . Of the Injlueiice of Temperature on Vinous Fermentation. 

 Twelve degrees of Reaumur's thermometer appears to be 



* About CO of Fahrenheit. 



the 



1 



