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Invert sugar is so called because the mixture of glucose and fructose which forms the "invert" is laevo-rotatory, whereas cane sugar is dextro-rotatory to the plane of polarized light. The preparation of invert sugar by the acid process consists in treating the cane sugar in solution with a little mineral acid, removing the excess of the latter by means of chalk, and concentrating to a thick syrup. The yeast process (Tompson's), which makes use of the inverting power of one of the enzymes (invertase) contained in ordinary yeast, is interesting. The cane sugar solution is pitched with yeast at about 55° C., and at this comparatively high temperature the inversion proceeds rapidly, and fermentation is practically impossible. When this operation is completed, the whole liquid (including the yeast) is run into the boiling contents of the copper. This method is more suited to the preparation of invert in the brewery itself than the acid process, which is almost exclusively used in special sugar works. Glucose, which is one of the constituents of invert sugar, is largely used by itself in brewing. It is, however, never prepared from invert sugar for this purpose, but directly from starch by means of acid. By the action of dilute boiling acid on starch the latter is rapidly converted first into a mixture of dextrine and maltose and then into glucose. The proportions of glucose, dextrine and maltose present in a commercial glucose depend very much on the duration of the boiling, the strength of the acid, and the extent of the pressure at which the starch is converted. In England the materials from which glucose is manufactured are generally sago, rice and purified maize. In Germany potatoes form the most common raw material, and in America purified Indian corn is ordinarily employed.
Hop substitutes, as a rule, are very little used. They mostly consist of quassia, gentian and camomile, and these substitutes are quite harmless per se, but impart an unpleasantly rough and bitter taste to the beer.
Preservatives.?These are generally, in fact almost universally, employed nowadays for draught ales; to a smaller extent for stock ales. The light beers in vogue to-day are less alcoholic, more lightly hopped, and more quickly brewed than the beers of the last generation, and in this respect are somewhat less stable and more likely to deteriorate than the latter were. The preservative in part replaces the alcohol and the hop extract, and shortens the brewing time. The preservatives mostly used are the bisulphites of lime and potash, and these, when employed in small quantities, are generally held to be harmless.
Brewing Operations.?The general scheme of operations in an English brewery will be readily understood if reference be made to fig. 1, which represents an 8-quarter brewery on the gravitation system, the principle of which is that all materials to be employed are pumped or hoisted to the highest point required, to start with, and that subsequently no further pumping or hoisting is required, the materials (in the shape of water, malt, wort or hops, &c.) being conveyed from one point to another by the force of gravity.
The malt, which is hoisted to the top floor, after cleaning and grading is conveyed to the Malt Mill, where it is crushed. Thence the ground malt, or "grist" as it is now called, passes to the Grist Hopper, and from the latter to the Mashing Machine, in which it is intimately mixed with hot water from the Hot Liquor Vessel. From the mashing machine the mixed grist and "liquor" pass to the Mash-Tun, where the starch of the malt is rendered soluble. From the mash-tun the clear wort passes to the Copper, where it is boiled with hops. From the copper the boiled wort passes to the Hop Back, where the insoluble hop constituents are separated from the wort. From the hop back the wort passes to the Cooler, from the latter to the Refrigerator, thence (for the purpose of enabling the revenue officers to assess the duty) to the Collecting Vessel,[4] and finally to the Fermenting Vessels, in which the wort is transformed into "green" beer. The latter is then cleansed, and finally racked and stored.
It will be seen from the above that brewing consists of seven distinct main processes, which may be classed as follows: (1) Grinding; (2) Mashing; (3) Boiling; (4) Cooling; (5) Fermenting; (6) Cleansing; (7) Racking and Storing.
