M. Lequin distinguishes two sorts, or rather two varieties of leaven, the one soluble in water, the other insoluble. The former abouuds in fruits, and forms the sweet principle of the grape; the other coustitutes the yeast of beer. In the progress of fermentation, the first seems to pass into the state of the second. It separates itself from the fermenting body, and is precipitated, forming the lees and scum, which appear in a liquor under fermentation.
In the sequel, then, this sweet substance, or principle, shall be called the leaven; and it will be seen, when treating of fermentation, that it is sufficient to put this leaven, and the saccharine principle or sugar, in contact with water, to determine fermentation; and that, to the very variable proportions in which they are respectively present, in the grapes submitted to fermentation, the differences in the phenomena, and results of their decomposition must be referred.
This leaven is almost inseparable from the saccharine principle in the products of vegetation. They are found almost universally united, and more or less intimately combined.
They are present, then, in the grape, but in very different proportions. In some grapes, the saccharine principle predominates; in others, the leaven. In the former case, fermentation produces sweet
