The consequences of worts being set to ferment at, in an undue heat, are the following. In strong beers, or such as are intended for long keeping, if the worts be too cold, a longer time is required for their fermentation, and the drinks grow fine with more difficulty; if, on the contrary, they are too hot, acidity, and a waste of some of the spiritous parts must ensue. Either of these disadvantages appears more conspicuous in common small beer, as, in winter, this drink is seldom kept a sufficient time to correct the defect, and in summer, from being too hot, it becomes putrid, or, in the terms of the brewery, is hereby _foxed_. SECTION XV. _Of Yeast, its nature, and contents, and of the manner and quantities in which it is to be added to the worts._ Musts, or worts, though ever so rich, when unfermented, yield no spirit by distillation, nor inebriate, if drank in any quantity. The oils, as yet not sufficiently attenuated for this purpose, become so only by fermentation. Air is absolutely necessary for this process, in the course of which, some of the aerial parts mixing with, and being enveloped by, oils greatly thinned, are enclosed in vesicles not sufficiently strong to resist the force of elasticity, or prevent a bursting and explosion. In the progress of the act, the air joins with oils both coarser, and charged with earthy particles, a coat is formed capable of resisting its expansion, and if the bubbles cannot come to a volume sufficient to be floated in and upon the liquor, they sink to the bottom, and take the appellation of _lees of wine_. Between these two extremes, there is another case, when the bubbles are sufficiently strong to hold the air, but not weighty enough to sink. After floating in, they emerge, and are buoyed upon the surface of the liquor, and there remaining entire, are termed the _flowers of wine_. Both lees and flowers are, therefore, vesicles formed out of the must, filled with elastic air, and, either separately, or when mixed together, they obtain the general denomination of _yeast_. We have often mentioned the power of fire, in driving the air out of worts. Yeast, fraught with the principle now wanted for fermentation, is, therefore, the properest subject to be added to the must; but its texture is various, in proportion to the different heats of the extracts it was formed from. Keeping drinks, extracted with hotter waters, yield yeast, the oils of which have a greater spissitude. It is consequently slower, more certain, and most fit to promote a cool and gentle fermentation. That, on the contrary, which is produced from small beer, being weak, and acting at once, is apt to excite a motion like that of effervescence; such yeast ought, therefore, not to be used, but when there is no possibility to obtain the other.