Of the extent to which the cooling power of a given area of wort surface is increased by the p.assage over it of a current of air, some idea may be gained from Dalton's experiments on evapora tion at natural temperatures. With water at 100°, and an atmospheric temperature of 15° it was found that a surface of about 27 sq. in., which would evaporate 2.1 grains a minute in st'lll dry air, would evaporate 3.3 grains a minute when there was a brisk current of air passm* g. When coolers are placed at an elevated pait of the brewery, as is very usually the case, they are generally subjected to natural currents of air of greater or less force ; but in addition to this it is the practice in many breweries to assist the cooling by the use of fans. Fans, having each three or four vanes, are caused to rotate horizontally immediately above the surface of the wort, the biadee or vanes being placed with their surfaces inclined to the plane of rotation so that the current of air is deflected downwards as well as caused to spread radially. Fans arranged in this way not only cause a constant change of the air in contact with the wort, but give rise to currents in the wort itself, and thus tend to equalize its temperature throughout.
Another arrangement for obtaining an artificial current of air over the wort has been adopted. A cooler is attached to each pair of mash tuns, and is of sheet iron, supported on open joists, so that the under sides are freely exposed to the air. At one comer of the cooler is a fan, communi cating with a wooden trunk, led along one side of the cooler, having openings through which the air can enter. The moiet air, drawn off by the fan from the surface of the wort, L9 expelled through a pipe, which rises through the roof of the building.
The best brewing practice is now tending to the employment of refrigerators alone for cooling the wort, and for this there are many reasons. A lengthened exposure to the atmosphere, to which the wort is subjected on the coolers, is far from beneficial, and in comparatively warm weather apt to induce acidity. There is also a loss by absorption on the coolers, and a lose by evaporation. As this latter loss is merely of water, it may, at first sight, appear to be of but small consequence ; in reality this is not the case. Under ordinary circumstances, the loss by evaporation alone is about 8 per cent., and this involves the use of 8 per cent. more liquor in washing than would otherwise be necessary to produce a wort of a given final strength. The quantity of wort to be boiled is also increased 8 per cent., and since the quantity of fuel used is, in large brewings, proportional to the quantity of wort and liquor heated, an additional consumption of 8 per cent. of fuel is the result.
When the wort is cooled entirely by passing it through a refiigerator, the loss by evaporation is of course nil. and since a less quantity of liquor will have to be used in mashing, there will be a less quantity to heat as liquor, and to boil afterwards as wort. In many cases, the hot water obtained from the refrigerators may be fed into the liquor boilers. Again, where fans are used, the expense of the engine power required to drive them has also to be considered.
Against tbe disadvantages of the coolers are to be set the expense of the refrigerator and tho cost of supplying it with water, either by pumping or otherwise ; in all but very exceptional cases, the balance will be in favour of the use of the refrigerator. In many instances, the water heated by passing through tho refrigerator can be used for brewing purposes, and even when the water used for refrigeration is not available for brewing, the supply of hot liquor can generally be turned to some account. Coolers are beet employed only for effecting the reduction of the temperature of the wort from boiling point to 43° (110° F.) or 50° (120° F.), the cooling being completed by a refrigerator.
In the cooling process, a precipitate is formed due to two causes, the simple action of cold being one. Part of the albuminous matter, that which combines with tannic acid to form tannate of albumen, is precipitated, the precipitate being also due to oxidation. During a long cooling from a high temperature, as when the worts are cooled upon open coolers, oxidation is set up by the air, the most dangerous temperatures being from 39° to 50° (100° to 120° F.). If starch is present in soluble condition it is likely to set up decay, which Graham states is not due to the action of vital organisms, but to the division of the grape sugar or glucose into two equal molecules, each containing C31-1,0„ or lactic acid ; tbe molecule of glucose simply breaks up into two mole cules of lactic acid, no gas being given off nor precipitate formed, but the acid is produced by simple alteration of the molecular arrangement. This action is likely to occur in a prolonged exposure to temperatures between 16° and 38° (60° and 100° F.). Rapid cooling therefore is essential.
Wort cooled on cooling floors is stated to be sound and good if it presents a black appearance on the surface, a reddish hue being indicative of putrefaction. When this red colour occurs, the ttolers must be thoroughly cleansed with chloride of lime and quick lime, not with bisulphite of lime. Graham considers that cooling should be continued to about 18° (64° F.) or 19° (66° F.). In Burton, it is carried to 11° (57° F.), and in Bavaria, where the bottom fermentation process is employed, to 6° (42° F.).