YEST, a head or foam rising upon beer or ale, while working or fermenting in the vat. See BREWING.
It is used for a leaven or ferment in the baking of bread, as serving to swell or puff it up very considerably in a little time, and to make it much lighter, softer, and more delicate. See BAKING, BREAD, and BARM.
The making of yeast was formerly a great desideratum in the arts; but of late Mr Henry has published a process, by which he says it can be originally produced without any previous fermentation. The process consists in impregnating a mixture of molasses and flour with fixed air; and this mixture is afterwards found to act as a ferment to other substances.