It may be regarded, as a rule, that the lower the temperature, and the slower, more regular, and less interrupted the process of fermentation, the better will be the quality of the brewing, and the less likely to change by age. A little more yeast is required in winter than in summer. When the fermentation becomes slack in the ‘gyle-tun,’ a little more ‘lobb’ is
generally added, and the whole is well ‘roused up,’ On the contrary, if the temperature rises considerably, or the fermentation becomes too brisk, the wort is cooled a little and skimmed, or at once cleansed.
5. Cleansing:—This consists in running the beer from the gyle-tun into casks, or other vessels, set sloping, so that the yeast as it forms way work off the one side of the top, and fall into a vessel placed below to receive it. In small brewings the beer is often at once transferred from the gyle-tun to the ‘store-casks,’ which are sloped a little until the fermentation is over, when they are skimmed, filled, and bunged.
The process of cleansing is generally commenced as soon as the ‘saccharine’ in the fermenting wort falls to about 10 lbs. per barrel, a degree of attenuation which it usually reaches in about 48 hours. Some brewers add a little wheat-flour or bean-flour (about 1⁄4 lb. per barrel) to the beer in the gyle-tun, shortly before cleansing, to quicken the discharge of yeast; but it is not clearly ascertained whether such a plan is advantageous, or the contrary.
6. Storing:—As soon as the fermentation is concluded, which generally takes from 6 to 8 days, or longer, the clear liquor is pumped into the store-casks or vats, which are then closely bunged, and deposited in a cool cellar, if not already there, to mature. The preference, which at present exists in most parts of the United Kingdom, is for mild, freshly-brewed malt liquors; the good old or mature-vatted beer being now seldom met with. This, of course, is a source of increased profit to the brewer, as it enables him to turn over his capital more rapidly, and saves the risk and expense attendant on long storage.
7. Ripening:—After a period varying from one to twelve months or longer, according to the nature of the brewing, and the condition of the cellar, the liquor will have become fine, and sufficiently mature for use. During this period the casks, &c., should be occasionally examined to see that there is no leakage, and to open the vent-holes, should any oozings appear at the joints. As equable a temperature as possible should be maintained in the cellar, by ventilation, on the one hand, and the employment of artificial heat on the other, as circumstances and seasonal changes may render necessary.
8. Fining or Clarifying:—Beer which has been badly brewed or badly stored, or which from other causes may be thick or muddy, requires clarifying by artificial means. For a barrel about 1 to 11⁄2 pint of brewer’s finings (isinglass or fish-gelatin dissolved in sour beer) is put into a bucket, and some of the beer being gradually added, the whole is violently agitated with a whisk until a frothy head is formed. The mixture is then thrown into the cask of beer, and well ‘rummaged up,’ after which the bung is replaced, and the liquor allowed to repose for a week or ten days.
Sometimes the above method is found to fail with weak and bad-conditioned beer. When such is the case, the addition of a teaspoonful of sulphuric acid, or a table-spoonful of powdered catechu (previously dissolved in 1⁄2 a pint of boiling water), followed by agitation for a quarter of an hour, will generally cause the ‘finings’ to clarify the liquor; 2 or 3 oz. of tincture of catechu (mixed with a little water) may be used in the same way. A handful of hops, previously boiled for five minutes in a little of the beer, and then added to the barrel, and the whole allowed to stand for a few days, before proceeding to clarify it, will generally have a similar effect, and cause the ‘finings’ to act with certainty. It is the absence of the proper quantity of astringent matter in beer that usually renders them ineffective.
M. Brescius employs tannin for the clarification of beer. To 1000 litres of beer he adds 140 grains of tannin dissolved in 3⁄4 of a litre of water, which is thoroughly stirred up. After three or four days he adds one litre of isinglass or two of gelatin in the proportion of 1 kilo. to 100 litres. The complete clarification requires about eight days.
Gen. commentary. The preceding is a concise account of all the essential operations of the system of brewing at present practised in this country. On the large scale, extensive and costly apparatus and machinery are employed for the purpose. On the small scale, various modifications, of a minor character, or the several processes herein detailed, are frequently adopted according to the circumstances or ingenuity of the operator. The principles and practice of brewing beer are, however, essentially the same under all the conditions here referred to. In Scotland, only one mash is made, and that at a temperature of about 180° Fahr., with one third of the quantity of the water required for the brewing. The ‘mash-tun’ is then covered up for about half an hour, when the wort is drawn off, and the operation of ‘sparging’ begun. This operation is continued until the density of the mixed worts becomes adapted to produce the quality of the ale then under process of manufacture. The ‘gyle-tun’ (fermenting-tun) is set at from 50° to 60° Fahr., the fermentation being continued slowly for fifteen to twenty days; and the ale is not ‘cleansed’ before the degree of attenuation falls to about 1⁄2 lb. per day, and not more than one fourth of the original gravity of the wort remains. Scotch ale is justly celebrated for its superior quality. Its usual original gravity is from 34 to 45 lbs. per barrel.