BREWING.—The process of brewing comprises four distinct operations, namely (1) mashing, or the preparation of the sweet wort ; (2) boiling, or the preparation of the bitter wort; (3) cooling, or the refrigeration of the worts ; and (4) fermentation. These operations will now be described in their order.
Before describing the process of mashing, it is necessary to deal shortly with the hoppers, by which the crushed malt, or grist, is received after it leaves the malt mills. These hoppers are termed grist cases, and were formerly constructed of wood, but are now generally of iron. The iron can best be employed in the corrugated form, as the corrugation gives stiffness, with but little bracing. The form varies considerably and is determined by circumstances ; in cases where special mashing machines are not employed, the mashing being wholly performed within the mash tun, the grist cases aro generally made to deliver the grist into the tun at four places. The lower part of each case is divided to effect separate delivery into four hoppers, each of which has its separate spout for the delivery of the malt. At Bass's brewery, at Burton, the grist is delivered from the case into the mash tuns, the grist case being placed directly over the mash tun. For porter brewing, as carried on at the City of London Brewery, the grist cases aro not in the same room as the mash tuns, but the grist is supplied to the tuns by shoots, passing through one of the walls, and constructed so as to be lifted up out of the way when not in use. Where mashing machines are employed, the circumstances determine the construction of the grist case.
There are many methods of conveying the grist from the malt mills to the grist case ; but these again are determined by the arrangement of the brewery, and will be dealt with under another heading.
Mashing.—The malt having been crushed in the malt mill, is treated to prepare for the operation of mashing a saccharine wort. This is effected by mixing the crushed malt with water of a certain temperature; the malt contains the peculiar principle of fermentation referred to above, diastase, which is, however, not a true ferment. This substance possesses the property of converting starch into dex trine, and by prolonged action, into sugar, and is the cause of the formation of the saccharine wort by the mashing process. Payen and Persoz have determined that it depends, whether the starch shall be converted into dextrine or into sugar, upon the time during which the malt is digested and upon the temperature.' They quote the following experiment as illustrative of the action. From 6 to 10 parts of finely ground malt are put into 400 parts of water heated to a temperature of 27° (80° F.), and 100 parts of starch are added, the mixture being stirred, and the temperature raised to 60° (140° F.). The temperature is again raised to 70° (158° F.), and maintained between that temperature and 75° (167° F.). In twenty to thirty minutes the solution, originally milky, becomes of a pasty consistency, and loses thickness. This loss of consistency takes place when the starch is converted into dextrine. In this condition, if the solution is rapidly raised to the boiling point, and sufficient water got rid of as steam, a thick gum is obtained. But if the solution, instead.of being raised to the boiling point,
is kept at a temperature of 70° to 75° (158° to 167° F.) for two or three hours, the starch, or the greater portion of it, will be converted into sugar. By removal of the water from this sugar solution, by evaporation at the same temperature, a syrup results resembling that produced by the action of sulphuric acid on a solution of starch. Substituting in this experiment, for the mixture of malt and starch, a mashing of malt alone, the diastase, having a smaller proportion of starch to act upon, more quickly yields a saccharine liquid. Pure diastase will convert 2000 times its own weight of starch into sugar, the thue of the action being inversely as the proportion of starch. This experiment illustrates in an important manner the operation of mashing, as it shows that by the duration of the mash, tbe wort may be made to contain greater or less proportion of dextrine uot converted into sugar.
Dextrine, like sugar, is fermentable, and can be converted into alcohol. Sugar is, however, easily fermentable; dextrine is only fermentable with difficulty, and it requires a greater proportion of ferment, and a higher temperature in the fermentation tun. Dextrine may be considered to exert such an influence on the fermentation of the wort as to enable the brewer, by its means, to control the action in the tun, and is specially valuable for his use in proper proportions. These proportions depend chiefly on the class of beer to be made, as well as upon the season of the year at which the brewing takes place. An entirely saccharine wort yields too energetic a fermentation for the brewer to keep the process, even at ordinary temperature, under control. In such a case the sugar is wholly decomposed, and the wort converted into alcohol and water, or if too much oxygen is absorbed, into vinegar. In worts containing dextrine in a certain proportion, there first occurs a fermentation, agreeing with fermentation commonly so termed, during which the sugar and dextrine together undergo transformation into alcohol. There also occurs a second period during which the fermentation of the dextrine is continued, after the sugar has been decomposed ; this period is productive in brewing of some of the most valuable properties of beer ; it may be termed the period of dextrinous or after-fermentation. This after-fermentation is mueh slower than that of the first period, and to it is due the briskness to the palate of good beer, even after the beer has been a considerable time in cask. Tho carbonic acid evolved during this fermentation prevents the absorption of oxygen, and consequently the formation of acid. Beer to be kept a long time requires great care to be paid to the after-fermentation, and should be prepared from wort containing a larger proportion of dextrine. Beers brewed for rapid consumption may contain a very large proportion of sugar, but on this account will not keep, especially in hot weather. The proportion of dextrine in the wort depends upon the brewer's particular trade, and to a great extent upon the class of beer he brews, regulated by the mashing process.