By the description given of the origin of yeast, it appears that it is formed rather of the coarser oils of the worts. If the cleansing is not done when the head is sunk down to half the greatest height it rose to, by falling lower, some part of these coarser oils return into the beer, then under fermentation, and gives it a flat, greasy taste, technically termed _yeast bitten_. When, on the contrary, beers or ales are removed too soon from the first tumultuous fermentation, for want of having been sufficiently attenuated, and from not having deposited their lees, nor thrown up in flowers their coarser oils, they are less vinous, than otherwise they would have been, appear heavy, aley, and are said _not to have their body sufficiently opened_. The fermentation of common small beer is, through necessity, carried on so hastily, that it is hardly possible to wait for the signs, which direct the cleansing of other beers. This drink being generally brewed and fermented within twenty four hours, its state, with regard to fermentation, is best judged of, by the quantity of its froth or head at the time of cleansing, which, in proportion to the heat of the air, may be determined by the following table. A TABLE _shewing the depth of head, which common small beer should have to be properly cleansed, in every season of the year_. Heat Head on the beer of the air. in the tun. 25 Degrees 6 inches. 30 5 35 4-1/4 40 3-1/2 45 2-3/4 50 2 55 1-1/2 60 1 65 3/4 70 1/2 75 1/4 80 just taken. As it is chiefly by the action of the air that wines are formed, if we contrive to shift this powerful agent on the surface of a must under fermentation, and to convey it more forcibly and hastily into the wort, its efficacy will be renewed, the fermentation accelerated, the liquor quickly become transparent, and soon be brought to the state of maturity age might slowly make it arrive at. Amber, or pale ales, require the hottest extracts pellucidity admits of to be made strong, and at the same time soft and smooth to the palate; but, as ales do not admit of any large quantity of hops, which would alter their nature, there is a necessity to perform hastily the act of fermentation, and to carry it on to a higher degree than is common in other malt drinks. The method of exciting and conducting repeated fermentations, with success, is perhaps not only the most difficult, but the most curious, part of the process, I shall therefore conclude, with an account of it, what I have to say with regard to the practice of fermentation.