Tbe action of this arrangement is as follows : When the worts are poured in, drainage.takcs place through the false bottom between the diaphragms in the usual manner ; and !D.. ad. dition to this the wort also passes through the vertical grilles or diaphragms ioto the end divisions of tbe back. From these latter it passes through the curved grilles, which serve to separate any hops that may have passed through the vertical diaphragms, and so into the space below the false bottom, and thence to the pumps.
NThen drawn from tbe hop-back, the wort has to be cooled to the temperature at which it is placed in the fermenting tun. This temperature varies from 12° to 18° (54° to 64° F.), and allowing for some loss of heat in the hop-back and communicating pipes, the temperature of the wort has to be reduced about 83° (150° F). This reduction is sometimea effected by exposing the wort to the air in shallow vesaels, or coolers ; sometimes by passing it through a refrigerator, and very generally by a combination of the tvro methods.
Wooden coolers are those most frequently met with, probably on account of cheapness, but they are open to many objections. They are usually made of Dantzic deals about It in. thick, the boards being pegged to the joint piecea with wooden pins. The coolers should be laid with a slight inclination towards the point at which the wort is dravrn off, and the boards should be planed as smooth as possible, so that they may be more readily kept clean. Too much care cannot be paid to the cleanliness of the coolers, and they should be frequently well washed with lime water. If the coolers are not in almost continual use, it is advisable to keep them covered with water when not required for the wort, as the pores of the wood, which have been opened by the action of the hot wort, are prevented from absorbing air which would come into contact with the next wort, and Cause incipient fermentation, generally termed foxing.
Metal coolers are generally placed so that their under sides are exposed to the air as well as the upper surface, and the cooling effect is thua increased. This arrangement should be adopted in all metal coolers. At Truman's, the coolers are of copper, and are two in number, ea,ch 110 ft. long by 25 ft. wide. They are made of thin copper, the weight a square foot being about 31 lb., and are supported merely on joists, the under aides beiug freely exposed to tbe air. The wort is not
allowed to remaio in these coolers, but is run over them in a thin atream to a refrigerator, which completes the cooling process. Theae coolers are capable, under ordinary circumstances, of cooling about fifty barrels of wort an hour from the boiling point to a temperature of 43° (110° F.) ; the combined surface of the coolers being 5500 sq. ft. This is a very high result, and is partly due to the wort being kept in circulation over the coolers, and to the coolers being made of thin copper.
Special rules for the dimensions of coolers are inadmissible. Besides the variations in tempera ture and state of the atmosphere, which exercise a most important influence on the efficiency of cooling surface, the position in which the coolers are placed, and the degree in which they are protected from free currents of air by surrounding buildings, modify considerably their refrige rating power. Coolers should always be placed so that the air bas free access, and to this end it is usual to make the walls of the rooms containing them of louvres, which can be opened as may be required. If the wort is to stand on the coolera, these should be of such size that the depth of the wort may not exceed 2 in. or 2i in., or, in other words, have an area of about 36 sq. ft. s. barrel, each square foot thus carrying a gallon of wort. When covered with wort to this depth, a well-situated cooler will, under ordinary circumatances, effect the required reduction of temperature in six to eight hours.
The cooling power of a certain area of cooler surface may be increased by causing the wort to flow over the coolers instead of remaining quiescent, or by causing the surface to be swept by an artificial current of air.
If coolers are worked in connection with a refrigerator, so that there ma.y be a regular flow of wort, they should.be of considerable length in proportion to the width, or if of nearly square shape, divided by partitions placed so as to leave passages past the alternate ends, so that the wort may have to travel through a series of long and comparatively narrow channels. The wort should be drawn off from different points in the width of the stream, either through a number of openings communicating with a single pipe, or by letting the wort fall over a kind of weir extending across the stream. By these means, greater uniformity of current will be ensured.