2. When these air bubbles are extended over the whole surface of the must, it is said to be _creamed over_. 3. Bubbles continuing to rise, a thin crust is formed; but as the fermentation advances rather faster near the sides of the tun, than in the middle, this crust is continually repelled; from which arises the denomination of _the wort parting from the tun side_. 4. When the surface becomes uneven, as if it were rock work, this stage of fermentation, which has no particular use, is distinguished by its _height_. 5. When the head becomes lighter, more open, more uniform, and of a greater depth, being round or higher in the middle, than in any other part, and seeming to have a tendency still to rise, the liquor is denominated to be of _so many inches, head not fit to cleanse_. 6. This head having risen to its greatest height, begins to sink, to become hollow in the middle, and, at the same time, more solid, the colours changing to a stronger yellow or brown; the wort is then said to be _fit to cleanse_. After this, no farther distinctions are made; if the fermentation is suffered to proceed in the tun, the head continues to sink, and the liquor is often injured. As the denominations and tastes of liquors brewed from malt are numerous, it is impossible to specify each separate one; we shall therefore only particularize such sorts of drinks, as were taken notice of in the section of extraction, they being most in use; but, from what will be said concerning them, the method of managing any other malt liquor may easily be deduced. Spontaneous pellucidity arises from a due proportion of the oils to the salts, in the worts, but the advantage of long keeping depends not only on the quantity of oils and hops the musts possess, but also on the fermentation being carried on in a slow and cool manner. All drinks, intended long to be kept, are therefore best formed in cold weather, and made to receive their yeast at such temperature, as is set forth in the table. The yeast is to be divided in proportion to the quantities of wort let down, until the whole, being mixed together, receives its allotted portion, except so much as is to be put in just before cleansing. Under these circumstances, drinks, which are brewed for keeping, are suffered to go through the first process of fermentation, till they are so attenuated, that the liquor becomes light, and the head, or the yeast, laying on the surface of the beer, begins to sink. When, or somewhat before, this head has fallen to nearly half the greatest height it reached to, a remarkable vinous smell is perceived, and the liquor, at this term, is to be put into casks, being first well roused with the remaining part of the yeast, in the manner mentioned in the preceding section.