When sugar is used it may be either mixed with the malt in the mash-tun, at the time of mashing, or put into the underback, just before setting the taps, and the hot wort run upon it. The proportions of malt and sugar vary according to the quality of the latter, but, on an average, from 170 lbs. to 200 lbs. of good raw sugar may be taken as the equivalent of a quarter of malt.
2. Boiling:—The wort is next transferred from the underback to the copper, and heated to the boiling-point as soon as possible, the object of this expedition being to prevent the formation of acid in the wort, by exposure to the air, before undergoing the changes which take place in the copper. As soon as the boiling of the wort commences the hops are added, and the boiling is continued for about 2 or 21⁄2 hours. A longer boiling is highly objectionable, owing to the extraction of a heavy, resinous bitter from the hop, and the danger of losing the volatile oil upon which the aroma depends. For mild beers the worts are seldom boiled so long; for strong keeping ales, sometimes a little longer. The boiling is known to be completed when the liquor ‘clears,’ as it is called, and albuminous flocks sink to the bottom of the copper.
The hops, strained from each wort, are returned into the copper with the following one.
The average loss by evaporation in the process of boiling varies from 1⁄6th to 1⁄7th of the original bulk of the wort. The gravity increases at the same time in about the ratio of 5 to 4; so that if the gravity be, at first, say 32 lbs. per barrel, it will at the end of the operation have risen to about 40 lbs.
3. Cooling:—The wort, under the common system, is ‘run off’ from the copper into the ‘hop-back,’ through a strainer which keeps back the hops. It is then pumped into large square shallow vessels called ‘coolers,’ where it is freely exposed to a current of air to reduce its temperature as quickly as possible, in order to avoid acidity or ‘souring.’ In 6 or 7 hours, or sooner, the temperature should fall to about 60° Fahr. In warm weather the depth of the liquor in the coolers should not exceed 3 or 4 inches; and in cold weather not more than 5 or 6 inches. As soon as the temperature has fallen to about 60° the liquor is ‘tunned’ and ‘yeasted.’
The loss by evaporation and condensation in the coolers varies from 13 to 18 galls. per quarter.
4. Fermentation:—The cooled wort is next run into the fermenting tuns or vessels (gyle-tuns). In small brewings these may be casks with one of their heads removed; but under any form they must not be more than 2⁄3rds filled. The yeast, previously mixed with a little wort, and kept until the whole has begun to ferment (technically termed ‘lobb’), is now added, and after agitation the vessel is covered up, and kept so, until the fermentation is well established. By this time the temperature has risen from 9° to 15°.
The quantity of yeast employed, and the temperature of the wort when it is added, differ in different breweries and for different kinds of beer. It seldom exceeds 2 lbs. per barrel unless the weather is unusually cold, or the yeast old or stale, when a larger proportion is required. The Scotch brewers generally take only 1 gall. of yeast to fully 4 hhds. of wort.
In England, the temperature at which the yeast is added varies from 55° to 65° Fahr. In Scotland, the common temperature is 51° to 52°. In cold weather the heat may be 5° or 6° higher than in mild and warm weather, and a little more yeast may also be advantageously employed. In cold weather ale is commonly tunned at 60°, porter at 64°, and weaker beers at 65° or 70° Fahr. In ‘warm weather’ strong beer should be 4° or 5°, and other beers 7° or 8° cooler than the ‘heats’ just mentioned. On the small scale, 1 to 11⁄4 pint of yeast may be used to every barrel of strong-beer wort, and 3⁄4 pint to every barrel of mild-beer wort.
The commencement of the fermentation is indicated by a line of small bubbles forming round the sides of the tun, and in a short time extending over the whole surface. A ‘crusty head’ soon forms, and then a ‘fine rocky head,’ followed by a ‘light frothy’ one. At length the head assumes a yeasty appearance, the colour becomes yellowish brown, and a vinous odour is developed. As soon as this last head begins to fall, the tun is skimmed every 2 or 3 hours, until no more yeast is formed. The object of this is, not only to check the violence of the fermentation, but also to remove a peculiar bitterness, with which the first portion of the yeast is impregnated. The beer is then put into casks, or ‘cleansed,’ as it is called. A minute attention to every stage of this process is necessary to secure a fine flavour and a brilliant beverage.