"In the fermenting rounds yeast is added to the wort, and the fermentation thus set up is allowed, in the Edinburgh system of brewing, to proceed for about four or five days, the temperature of the wort being kept within proper limits by the use of the attemperators or coils of pipes, through which cold water can be passed. During fermentation a portion of the saccharine matter in the wort is converted into alcohol, and carbonic acid is at the same time evolved. The reduction of the saccharine matter, or "attenuation," as it is called, is accompanied by a rise in the temperature of the wort, and it is this increase in temperature which has to be kept under control by the use of the cold-water pipes we have mentioned. When reduced to within two or three degrees of the required attenuation the contents of the rounds are run into the cleansing squares, where the beer deposits its yeast, becomes gradually cooled and fined, and in from twenty-four to thirty-six hours is fit to be drawn into casks, when hops are added to it, and it is stored or sent out to customers, as the case may be.
It is in the mode of conducting the fermentation, more perhaps than in any other portion of the brewing process, that the difference between the various so-called systems of brewing followed in this country exists. What is termed the Scotch, or, more properly, the Edinburgh system of brewing, which we have above described, is but the continuation or growth of a system of fermenting and cleansing began and practised on a small scale a long time ago. Formerly, the Edinburgh brewers used only the fermenting rounds, and cleansed from them direct into the casks sent out to their customers, the fermenting and cleansing or settling occupying from one to three weeks, according to the state of the weather and the quality of the ale. The ale so cleansed was quite "fine," and required no "topping up" in the casks. Now, however, the use of cleansing squares, such as those shown in our engravings last week, has become almost universal in Scotland, and, in fact, entirely so in the eastern parts; and the whole operation of fermenting and cleansing is completed in about a week. In the Edinburgh system the fermenting rounds are always kept of moderate dimensions or comparatively shallow; their capacity seldom exceeding forty barrels, or, if they are larger, they are made of such a diameter as to contain the required quantity of worts without the depth exceeding about 4 ft. This enables the temperature of the fermenting wort to be controlled with a moderate amount of refrigerating power.
The London system is in many respects the reverse of that practised in Scotland, the business of brewing being carried on in the metropolis on a gigantic scale, and the plant employed being large in proportion. Thus the fermenting rounds have been allowed to grow with the coppers, and quantities as large as from 600 to 800, or, in some cases, considerably over 1000 barrels are fermented in one tun, the depth being often from 12 ft. to 15 ft. With such large quantities the heat becomes uncontrollable, and subdivision into pontoons or their equivalents is a necessity. The "double square" system prevailing through the north and west of England is the same in principle as the old Edinburgh method. The double squares in which the fermentation is carried are, as it were, made by dividing an ordinary square at the middle of its depth, and making the upper part a yeast chamber, whilst the pumping of the beer from the lower to the upper square, and thus mixing it with the yeast to stimulate it, is somewhat analogous to the rousing of the yeast into the beer practised by the Edinburgh brewers for the same purpose. The Burton and some other English brewers follow the London subdividing system, but, instead of the pontoons or cleansing rounds, they employ the well-known "union casks." In the case of the Burton brewers it is the practice to stimulate the gyles with large proportions of yeast, and to thus bring about very much the same result as is obtained in London breweries by the large bulk contained in the fermenting rounds. There are, however, some other peculiarities connected with the Burton system, of which, together with special points in other systems, we shall speak in due course."
"Engineering, Volume 5 - from January to June 1868", 1868, page 464.
Wasn't that fascinating? Let's pick through the bones and see what meaty tidbits we can find to chew.