This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
The clarifying of the beer is another feature in the art and process of making these light, fermented beers, that must receive considerable attention. Strong beer, made from malt and hops, ferments so slowly that sufficient time is obtained for it to "fine," as it is termed - in other words, for the yeast, dirt, foreign matters, etc., to either precipitate or rise to the top, or both, and become clear and transparent. Beer made from sugar or molasses at a high temperature ferments so rapidly, and consequently sours so quickly, that sufficient time is not allowed for the fining process; and especially beer made from oils which have a milky appearance from the particles of oil suspended in the liquid; but this matter can be remedied, in a great measure, by leaching the beer through a foot or more of clean, pure, white sand, or filtering through a felt or flannel bag. The beer is thus cleared of the yeast in a measure, sufficient remaining in the liquid, however, to finish fermentation in the bottle, and the beverage, after a lapse of forty-eight hours, is sparkling and lively, and produces a natural "head". It removes all the dirt, dead yeast and impurities, and the beer, if made from an extract properly prepared, will look as clear and transparent as wine. The taste is greatly improved as well as the appearance. Another advantage is, the beer keeps sweet much longer, and improves with the age to a certain extent. The filtering must never be done until the beer is worked smart and thoroughly alive, otherwise the fermentation will be stopped and the beer will be dead. After filtering, bottle and cork tightly, and let it set in a moderately warm place until it comes up in the bottles, and is smart and lively, which may require a day or two, or a longer period. If you want it to come up quickly, keep it warm; if you want it to keep a long time, keep it on ice or in a cool place. By this process you get the fermentation, which gives that fine sparkling appearance and flavor to bottled ale, cider and champagne. By careful working, all the light after-fermented beers that contain any body or substance can be kept as long as cider, ale or champagne; they can be worked to make as good a beverage as the grape vine, when prepared and handled with the same amount of skill.
The preservation of these beers is accomplished, to a certain extent, by the skillful manipulation of the preparation in the course of its process, and a good worked beer will always last longer than one that has not worked well. The addition of certain substances, such as salicylic acid, peroxide of hydrogen, hypo-sulphurous acid, bi-sulphate of lime, and numerous others, which tend more or less to check the fermentation, have always aided the bottler and brewer in this particular way, although it is not always recommended to make use of them, especially not the latter mentioned one, which is even very objectionable, although most applied, and particularly for cider, on account of its effective working and low price at which it can be bought. A very good preservative is made by dissolving one ounce of salicylic acid in three ounces of alcohol, and adding it to a barrel of beer that has been properly worked and filtered; this will preserve and keep the beer much longer. This addition is not generally necessary, being only required where the goods are stocked for some considerable time, and should only be added when racking off for bottling.