Description of the malt kiln.—[Figs. 97], [98], [99], [100.] exhibit the construction of a well-contrived malt kiln. [Fig. 97.] is the ground plan; [fig. 98.] is the vertical section; and [figs. 99.] and [100.], a horizontal and vertical section in the line of the malt-plates. The same letters denote the same parts in each of the figures. A cast-iron cupola-shaped oven is supported in the middle, upon a wall of brickwork four feet high; and beneath it, are the grate and its ash-pit. The smoke passes off through two equi-distant pipes into the chimney. The oven is surrounded with four pillars, on whose top a stone lintel is laid: a is the grate, 9 inches below the sole of the oven b; c c c c are the four nine-inch strong pillars of brickwork which bear the lintel m; d d d d d d are strong nine-inch pillars, which support the girder and joists upon which perforated plates repose; e denotes a vaulted arch on each of the four sides of the oven; f is the space between the kiln and the side arch, into which a workman may enter, to inspect and clean the kiln; g g, the walls on either side of the kiln, upon which the arches rest, h, the space for the ashes to fall; k, the fire-door of the kiln; l l, junction-pieces to connect the pipes r r with the kiln; the mode of attaching them is shown in [fig. 99.] These smoke-pipes lie about three feet under the iron plates, and at the same distance from the side walls; they are supported upon iron props, which are made fast to the arches. In [fig. 98.], u shows their section; at s s, [fig. 99.], they enter the chimney, which is provided with two register or damper plates, to regulate the draught through the pipes. These registers are represented by t t, [fig. 100.], which shows a perpendicular section of the chimney. m, [fig. 98.], is the lintel which causes the heated air to spread laterally instead of ascending in one mass in the middle, and prevents any combustible particles from falling upon the iron cupola. n n are the main girders of iron for the iron beams o o, upon which the perforated plates p lie; q, [fig. 98.], is the vapour pipe in the middle of the roof, which allows the steam of the drying malt to escape. The kiln may be heated either with coal or wood.
The size of this kiln is about 20 feet square; but it may be made proportionally either smaller or greater. The perforated floor should be large enough to receive the contents of one steep or couch.
The perforated plate might be conveniently heated by steam pipes, laid zig-zag, or in parallel lines under it; or a wire-gauze web might be stretched upon such pipes. The wooden joists of a common floor would answer perfectly to support this steam-range, and the heat of the pipes would cause an abundant circulation of air. For drying the pale malt of the ale brewer, this plan is particularly well adapted.
The kiln-dried malt is sometimes ground between stones in a common corn mill, like oatmeal; but it is more generally crushed between iron rollers, at least for the purposes of the London brewers.
The crushing mill.—The cylinder malt-mill is constructed as shown in [fig. 101], [102.] I is the sloping-trough, by which the malt is let down from its bin or floor to the hopper A of the mill, whence it is progressively shaken in between the rollers B D. The rollers are of iron, truly cylindrical, and their ends rest in bearers of hard brass, fitted into the side frames of iron. A screw E goes through the upright, and serves to force the bearer of the one roller towards that of the other, so as to bring them closer together when the crushing effect is to be increased. G is the square end of the axis, by which one of the rollers may be turned either by the hand or by power; the other derives its rotatory motion from a pair of equal-toothed wheels H, which are fitted to the other end of the axes of the rollers. d is a catch which works into the teeth of a ratchet-wheel on the end of one of the rollers (not shown in this view). The lever c strikes the trough b at the bottom of the hopper, and gives it the shaking motion for discharging the malt between the rollers, from the slide sluice a. e e, [fig. 101.], are scraper-plates of sheet iron, the edges of which press by a weight against the surfaces of the rollers, and keep them clean.
Instead of the cylinders, some employ a crushing mill of a conical-grooved form like a coffee mill, upon a large scale. (See the [general plan], infrà.)
The mashing and boiling.—Mashing is the operation by which the wort is extracted, or eliminated from the malt, and whereby a saccharo-mucilaginous extract is made from it. The malt should not in general be ground into a fine meal, for in that case it would be apt to form a cohesive paste with hot water, or to set, as it is called, and to be difficult to drain. In crushed malt, the husk remains nearly entire, and thus helps to keep the farinaceous particles open and porous to the action of the water. The bulk of the crushed malt is about one-fifth greater than that of the whole, or one bushel of malt gives a bushel and a quarter of crushed malt. This is frequently allowed to lie a few days in a cool place, in order that it may attract moisture from the air, which it does very readily by its hygrometric power. Thus, the farinaceous substance which had been indurated in the kiln, becomes soft, spongy, and fit for the ensuing process of watery extraction.