Drying the 111,11t.—This is effected in a room called a kiln.' Here the grain is spread out in a layer about 12 in. thick, and subjected to a temperature beginning at 35°, but increasing to 55° or 60', until the grain is nearly dry,.when it may be still further raised to 80° or 90°. The germinated and dried barley is called malt ; it is known to be of good quality when the grain is round and. full of flour ; when the skin is very thin ; and when it has an agreeable odour and sweetish taste. Pale malt, or that which has not been altered iu colour by heat, is the heaviest and best for distillation.
Grinding.—The dried malt must be coarsely ground on a mill, in order that none of the grains may escape fermentation; it is not necessary that they should be reduced to flour. If the grain be raw or unmalted, it must be ground more finely, so that it may be thoroughly penetrated by water, in the subsequent operations, and the starch more readily converted into sugar by the action of the diastase. The grain must not be ground until it is required for use, as it is liable to become musty, in which condition it loses much of its fermenteseible property.
Mashing.—After being crushed, the malt, together with the other grains, is placed in a vat, and warm water is run in, in small quantities at a time, in about the proportion of a litre to every kilo. of flour ; its temperature should bo about '35° to 36'. During the entrance of tho water the mass is well stirred, so as to cause the whole of the grain to be thoroughly soaked, and to prevent the formation of lumps. The vat must then be covered tightly and left for twenty or thirty minutes.
It usually requires three mashings to extract the whole of the saccharine and fermenteseible matters contained in the grain. In some places, it is customary to boil down the liquors from the three mashings until they have acquired a specific-gravity of about 1.05, the liquor from a fourth wash being kept back for the next mashing. Some distillers use enough water in the first two mashings to bring the whole to the correct degree for fermentation, the liquors from the third and fourth being boiled down to the same density and then added to the rest. In a large Glasgow distillery, the charge for the mash-tun is 260 cwts. of grain together with the proper proportion of malt. Two mashings are employed, about 28,300 gallons of water being required; the first wash ing has a temperature of 60°, and the second that of 80°. In Dublin, the proportion of malt employed is only about one eighth of the entire charge. One mashing is employed, and the temperature of the water is kept at about 62°. The subsequent mashings are kept for the next day's brewing.
Infusion.—The object of this important operation is the conversion of the starch of the grain into sugar by means of the diastase contained in the malt. To effect this, boiling water must be poured into the vat until the temperature of the mass reaches about 60° or 70°, the whole being well stirred meanwhile ; when this temperature has been reached, the vat is again covered and left to stand for four hours, during which time the temperature should, if possible, be maintained at 60°, and on no account suffered to fall below 50°, in order to avoid the inevitable loss of alcohol consequent upon the acidity always produced by so low a temperature. In cold weather the heat should, of course, be considerably greater than in hot. It should be also remarked that the greater the quantity of water employed, the more complete will he the saecharification, and the shorter the time occupied by the process.
Having undergone all the above processes, the wash is next drawn from the mash tin into a cistern, and from this it is pumped into coolers placed at the top of the building. These coolers consist of shallow iron vessels, or, in some eases, of copper tubes kept cool by water. When the wash has acquired the correct temperature—viz. from 20° to 26°, according to the bulk operated upon—it is run down again into the fermenting vats situated on the floor beneath. 5 or 6 litres of liquid, or 21 to 3 kilos. of dry brewer's yeast are then added for every 100 kilos. of grain; the vat is securely covered, and the contents are left to ferment. The process is complete at the end of four or five days, and if conducted under favourable conditions there should be a yield of about 2S litres of pure alcohol to every 100 kilos. of grain employed.
187.
The apparatus used in England for the distillation of grain-spirit is known as " Coffey's" still ; and is shown in Fig. 187. It consists of two columns, CHEF and G H J K, placed side by side, and above a rectangular chamber, containing a steam-pipe I from the boiler A. This chamber is divided into two compartments by a horizontal partition, pierced with small holes, and furnished with four safety-valves e e e e. Tho column C D E F, called the analyzer, is divided into twelve small compartments, by means of horizontal partitions similar to the one beneath, also pierced with boles and each provided with two little valves f. The spirituous vapours passing op this column are led by a pipe to the bottom of the second column or rectifier. This column is also divided into compart ments in precisely the same way, except that there are fifteen of them, the ten lowest being separated by the partitions Ic, which are pierced with holes. The remaining five partitions are not perforated, but have a wide opening as at w, for the passage of the vapours. Between each of these partitions passes one bend of a long zig-zsg pipe m, beginning at the top of the column, winding downwards to the bottom, and finally passing upwards again to the top of the other column, so as to discharge its contents into the highest compartment. The apparatus works in the following way : The primp Q is set in motion, and the zig-zag pipe then fills with the wash or fermented liquor until it runs over at n'. The pump is then stopped, and steam is introduced through h, passing up through the two bottom chambers and the short pipe z into the analyzing column C D E F, finally reaching the bottom of the other column by means of the pipe i. Here it surrounds the coil pipe containing the wash, so that the latter becomes rapidly heated. When several bends of the pipe have become heated, the pump is again set to work, and the hot wash is driven rapidly through the coil and into the analyzer at n'. Here it takes the course indicated by the arrows, running down from chamber to chamber until it reaches the bottom ; none of the liquor finds its way through the perforations in the various partitions, owing to the pressure of the ascending steam. In its course downwards the wash is met by the steam, and the whole of the spirit which it contains is thus converted into vapour. As soon as the chamber B' is nearly full of the spent wash, its contents are run off into the lower compartment by opening a valve in the pipe V. By means of the cock N, they are filially discharged from the apparatus. This process is continued until all the wash has been pumped through.