The millstones in common use, are of that kind of stone, called Cullen stones; a pair of which, three feet three inches diameter, will, with the power of about four horses, grind about 12 quarters, of eight bushels each, per hour. A pair of iron rollers, or about 27 in ches in length and 10 inches diameter, will crush 13 quarters per hour, and require about the same power as the millstones. Sonic breweries have lately employ ed steel mills, of the same kind with those used for grinding coffee but on a larger scale. A mill of this kind, of 10 or 12 inches diameter, and performing about 150 revolutions per minute, will grind six or eight quarters of malt per hour, in a very perfect manlier. It cuts the grains in the same manner as the millstones; but the malt passing very quickly through the steel mill, the divided parts of the corn are not rubbed to flour, as in the millstones, by being so long under the action of the machine.
The object of this process is to extract from the malt all the saccharine matter, and a certain part of farinaceous substance ; on the due proportion of which, the proper fermentation of the wort and flavour of the beer in a great illeaStI•C depends. This is done by two, three, four, and sometimes five, repeated infusions of hot water ; the heat of which being properly suited to the nature of the malt, will produce the desirable mix ture of fermentable matters ; and in this point the skill of the brewer is chiefly shown, as from the variable na ture of the malt it cannot be reduced to any absolute rule ; but he must in all cases proceed, in a great de gree, according to the existing circumstances.
Cold water will extract front the malt only a portion of those constituent parts which it is the object of the brewer to obtain; and on the other hand, boiling water. which is the greatest heat that can be employed, will have a tendency towards what is called se'ting the goods; and when applied to some kinds of malt, will actually produce this effect. This takes place, [helm the whole mass of malt in the mash tun mixes with a certain quantity of the water, and forms a pulp or paste, by dissolving the gluten contained in the malt, which is so viscous as to retain almost all the saccharum of the malt, and holds a great proportion of the liquor, so that it will not run out ofthe mash tun. The boiling liquor, therefore, will neither produce wort of a good quality, nor in any considerable quantity. Between these ex tremes of temperature, a proper medium must be sought. It should be so adapted to the malt, as to pro
duce a sweet wort, possessing the colour of the malt from which it is taken, and at the same time transpa rent when in the underback. Many practical brewers form a judgment of the proper degree of heat, from the wort in the underback bearing a frothy head; but this must be considered as a vague and indefinite crite rion. f he proper degree of heat will give the strongest wort, and in the greatest quantity ; for, if the heat is greater, though the strength of the wort is increased, a greater quantity of wort will be retained among the malt, in consequence of its tenacity. A heat too low will, indeed, produce more wort than the proper me dium; but it will be deficient in the fermentable mat ter which it ought to have extracted from the malt, and. in consequence of this, the beer will be spiritless, and liable to turn sour if kept.
The process of brewing has, of late years, been great ly improved by the application of the thermometer, to determine the degree of heat proper for mashing; but it is extremely difficult to fix with precision what this should be, as it depends upon the combination of so many circumstances. The great advantage, there fore, of the thermometer appears to be, that, when the brewer has by experience succeeded well in a brewing, he may know how to produce the same effect another time. The circumstances to be taken into considera tion are, First, the quality of the malt, the manner in which it has been dried, whether brown or pale, and also the per fection of the 'nailing, by which process the gluten con tained in the barley is in part converted into saccharum; and the degree in which this takes place will have sonic effect upon the mashing heat. The danger of setting the goods wholly or partially, will be in proportion as the malt is well or ill made, from its containing more ur less gluten, in proportion to the saccharum; and, therefore, well made malts may be mashed at the high est heats. The heat in which malt has been dried is, by Mr Combrune, made the ground of a calculation to determine the heat of the mashing liquor. He states the lowest heat for drying malt to be 120 degrees for very pale malt, and the highest, which is brown malt, at 150; and he assumes as a principle, that the heat f the extracting liquor should always be in proportion to that in which the malt was dried.