This process is now modified by the adoption of " cleansing squares," into which the ale is dis charged from the fermenting rounda, when within two or three degreea of the required attenuation. In the cleansing squares, the ale deposits its yeaat, and bccomea cool and is fined. From the squares it is drawn off into casks. Both the fermenting rounda and the cleansing squares are, in the beat arranged breweriea, fitted with attemperators, for reducing the temperature of the ale. The amount of refrigerating power required in these atternperatora ia small, for the fermenting rounds are almost always of very moderate capacity, seldom exceeding 40 barrels, and if larger, they are still shallow, and have large exposed surface; consequently a considerable loss of heat by radiation occurs. The depth of the ale in the tuns is aeldom more than 4 feet ; the wort is usually pitched at a temperature of frorn 11° to 14° (52° to 57° F.). The fermentation in the rounds generally occupies from four to six days, during which time the temperature increases to 21° or 22° (70° or 72° F.). The cleansing in the squares occupies from 24 to 36 hours.
In Yorkshire, and the northern and southern countiea of England, a system known as the stone or double-square system is very largely used. Fermentation is carried on in a somewhat deep square, divided at the middle of ita depth by a horizontal partition in which is an opening. The worts are enntained in the lower portion of the square, and the upper division is used as a chamber, into which the yeast rises through the opening. The beer is occasionally pumped from the lower chamber of the square into the upper one, where it becomes mixed with the yeast and again flows down into the lower compartment. The squares are commonly of atone, and the double square in which the fermentation proceeds is enclosed in another larger square, a space being left between the two into which water can be admitted for regulating the temperature. In the double square system, the beer is kept during fermentation at a temperature of about 13° or 14° (56° or 57° F.), and this temperature, when the desired attenuation has been reached, is reduced to about 56° by causing water to circulate through the exterior chamber and through atternperating pipes immersed in the liquid. This temperature is maintained during cleansing.
In the large porter breweries, the fermenting tuns are of very great capacity, in some instances 1500 barrels. The uaual capacity is between 200 and 700 barrels. These tuns are almost always of wood. Timber ernployed in the construction of tuns should be well seasoned, or the sap will mix with the wort and injuro it. The round tuns are made of staves held together by hoops like those of a cask, the bottoms being supported by the beams on which the tuns rest. In the case of the square tuna, the planks are fastened together by bolts, and the sides are connected by cross stays stiffened by external beams. Square tuns have the advantage that they can be stowed with less
waste of room than round tuns; but the round form is the best for wooden tuns, and should always be adopted where space perrnita. Fermenting tuna are generally fitted with attemperaters. A common plan is to earry these pipes round the tun at a short distance from the aides, and to support them by braekets. Attemperators are somctimea fitted across the tun, and when thus fitted are very efficient, as the cooled wort deacenda and gives the warmer currents free access to the pipes. Before the plan of fitting the tuns with attemperating pipea came into use, the somewhat clumsy expedient of immersing in the wort caska filled with hot or eold water was employed for the purpose of accelerating or retarding the fermentation. The casks so used were termed "nursea," and are still used iu aome breweries.
At Rcid's brewery, the tuns, instead of being open at the top, are completely elosed, with the exception of a small opening left for sampling ; the carbonic acid gas evolved during fer mentation is led off by descending pipes into a reservoir, where it ia stored. From this reservoir it is drawn off at intervals into indiarubber bags, whence it is supplied to the Aerated Bread Company for the manufacture of bread on Dr. Dauglish's system.
At some of the London breweries, large quantities of iee are used in summer time to lower the temperature during fermentation, as well as fir preserving the yeast. In the ease of the fermenting wort, the ice is used both to cool the air of the tun room aud alai the wort itself ; in the latter ease being commonly immersed in the wort, which is made of greater strength in order to allow for the reduction of gravity caused by the admixture of the melted ice.
Where large quantities of wort are collected in the fermenting tun it would be more or lesa diffi cult. to complete the fermentation satisfaotorily in these vessels; and it is therefore the praetice, amongst London brewera, after the fermentation has proceeded to a certain extent, to divide out the beer from the large tuns into a number of pontoons or cleansing rounds, having a capacity of about five to twelve barrels each. Stout, for instance, having an original gravity of, say, 32 lb. a barrel, is usually pitched at a temperature of 13° or 14° (56° or 57° F.), the quantity of yeast added being about li lb. a barrel. The attenuation is allowed to go on in the fermenting tuna until the gravity is reduced one-half. The beer is then divided out into the cleansing rounds, where the fermenta tion is completed, the final gravity being for ordinary Loudon trade 9 lb. or 10 lb. a barrel. With porter, the original gravity is usually from 20 lb. to 22 lb. a barrel, and the fermentation ia con tinued until the gravity is reduced to about one-third; the quantity of yeast added is only about 1 lb. a barrel.