When the heat of the atmosphere is more than 60 degrees, the cool of the night must be chosen to put the wort to work. In lower degrees of the atmosphere. the wort must be set at a greater heat than that of the air ; for, as the tendency to fermentation increases with the heat of the weather, it is necessary to correct this tendency, by putting the liquor to work colder in hot weather, and hotter in cold weather If the air is at 30° of FArenheit, small beer should be pitched or set to work at ,,bout 70° ; beer intended for keeping, at 56' ; and amber, or glutinous ales, at 54'. When the air is at all these kinds of beer may be set to work at 50°. in the process of fermentation, the temperature of the wort is often increased as much as 10° ; and it may in general be considered, that the wort will be 10' higher at the height of the fermentation than it was when first put to work, supposing the heat of the air continues the same.
The quantity of yeast has some effect on the degree of the fermentation : a greater quantity will increase the rapidity of the process, in the same manner as a greater degree of heat would, and vice versa ; hence a greater proportion of yeast is required in winter than in summer. The quantity which will be required at 80°, will be only one-half of that requisite to produce the same effects at 40°. Small beer, not intended for keeping, when the temperature is as low as 40°, will require about eight pints of yeast to the extract of one quarter of malt ; at 60° six pints ; and at 80° only four points.
Beer intended to be kept ten or twelve months will not require so large a proportion. Six pints at 40°, five pints at 60°, and three pints at 80°, will be found sufficient. The fermentation in the gyle tun having ad vanced to that state iv hen the head begins to decline, slims that the vinous fermentation is ended. if the beer is not cleansed just at this period, it will become yeast bitter, which gives it an unpleasant flavour, pro bably from the grosser parts of the yeast being absorb ed again in the liquor. The time when these signs will appear varies with the fermenting heat. At 60° it will sometimes require forty hours for the fermentation, though at a greater heat twenty or twenty-four are enough. The liquor is now possessed of some spirit, but is still unpalatable, from the mixture of extraneous farinaceous matter ; the wort having parted with noth ing in the fermentation but carbonic acid gas. Though the mucilage of the yeast is thrown up in part, it returns again ; but the mode of its existence is changed, from the chemical solution it had in the wort, to mechanical mixture : At least this change is partially effected, as is shewn by the turbid appearance of the liquor. If the beer were suffered to remain in the gyle tun, the acctous fermentation would take place, the spirit or al cohol at one time visible in the beer would be lost, and acidity produced. After the acetous fermentation, the beer, under certain circumstances, would produce vine gar, but not in general, for the W ort intended for beer has too much of the farina of the malt extracted in the mashing ; and the addition of the hops, if in sufficient quantity, will totally prevent it from becoming good vinegar, though it may acquire too much acidity to be drunk, and at the same time bitter, and perhaps putrid in sonic degree, from the early decomposition of some of its constituent parts ; for the acctous fermentation is followed by the putrefactive, which effects a total de composition of the beer, leaving a putrid disorganized liquor, unlit for any purpose.
Of Cleansing The object of cleansing is to stop the fermentation at the proper period, which is effected by drawing off the beer into smaller vessels, usually small casks. This lowers the temperature ; for, as the action of fermenta tion produces an internal heat in the liquor, it follows, that this heat will be diminished by dividing it into smaller quantities, when, by the casks exposing a great er surface to the external air, the heat is allowed to es cape. Notwithstanding the diminished heat, the dis turbance of the beer renews the fermentation, probably by incorporating with it the yeast which remained near the surface of the gyle tun. In cleansing, the cask being full, the head of yeast, which rises, flows off im mediately at the bung-hole, thus relieving the beer of its dregs, and perfecting the production of spirit which was begun in the gyle tun. As the quantity of beer in the cask constantly diminishes, it is filled up again ; and by this means no room is left for a head of yeast to float upon the liquor, but it must flow off and escape as fast as it is produced. This diminishes the tendency to fer mentation, which ceases spontaneously in a few days, more or less, in proportion to the heat of the atmosphere ; and the beer is ready for storing, and will be fit for the table when it has become quite fine. From what has been already mentioned, it will be seen, that it is of great consequence to keep the casks always completely filled. In the brewery (Plate LXXV11,) this is ac complished by an ingenious contrivance, which requires no attention. The cleansing batch, marked 8, Fig. 2, is left with a quantity of liquor in it, after the rounds 9 9 are all filled, which is done by one pipe 10 commu nicating with them all ; and therefore the liquor stands at the same level in all. A small square cistern is plac ed by the side of the batch, also communicating with the pipe, and a copper ball floats upon the surface of the liquor in it. The ball is connected by an iron rod, with a valve in the bottom of the batch, which, when open by the sinking of the float, admits the beer to flow into the rounds, till, by raising the surface of the liquor, the float closes the valve. The rounds have close heads, with a small square tube rising up about six inches from it, and having a spout to convey away the yeast. The liquor is adapted to stand some height in this tube, and thus, by means of the float, ensures that the beer shall never have a surface for a head of yeast to gather upon. This is a considerable improvement upon the common method, in which a great number of casks are put upon a frame called a stillion, with their axes placed horizontally, and the bung-hole upwards. They are filled by a hole from the squares; and a man is con stantly going round among them, to fill them up as they work off. This method, independent of the expense and trouble, is not so perfect as the one above described. The contents of the rounds 9 9, as drawn in the Plate, is too great to work the beer to the best effect, especially in summer. They may, however, be made much small er, without altering the principle.