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.
Originally in the Scotch, or Edinburgh system, fermentation and cleansing both took place in small rounds. No intermediate vessels were used between the rounds and the trade casks. However, by the time the article was written (1868) most Scottish brewers had introduced settling squares for cleansing. This sounds very much like the dropping system. Fermentation begins in a tall round fermenter and later the wort is dropped into a shallow settling square below (hence the dropping bit of the name) were fermentation is completed and the yeast settles out.
Except there's one big difference. In the dropping system as practised at Fullers and some other Southern breweries, the wort remained for only a short period in the round. Typical was 24 hours in the round and 5 or 6 days in the settling square before racking. In the Scotch system described above, the wort stayed in the rounds until fermentation was almost completed.
I'm sure that some of the differences were, as the author explains, due to the difference in scale between brewing in London and Scotland. As we've seen, the largest London brewers produced as much as all of Scotland. Their breweries had been designed to churn out enormous quantities of Porter and everything was on a grand scale. Even a comparatively small brewer like Fullers had fermenting vessels capable of holding more than 200 barrels.
Preventing the temperature of the wort seems a recurring theme. Hence the shallow Edinburgh rounds. Being shallow is probably also the reason why they'd been able to get away without using settling squares initially. Yeast will settle more rapidly in such a vessel. You could see this type of fermenter as a round and settling square combined. Looking at William Younger's brewing records from 1868, I can see confirmation of the small fermenter size. The largest wort I can find was 55 barrels. Most were 40-odd barrels.
I've just been taking a closer look at those Younger's records. And I think this text has helped me understand them better. Their worts spent 3 to 5 days in the fermenting tun and then 1 to 3 cleansing in a square before racking. The fermentation was in most cases, as the text says, within a few degrees of their final attenuation. Mostly just a couple of degrees (in SG). For example, 1036º to 1035º; 1030º to 1025º; 1017º to 1013º; 1017º to 1016º.
I think we all know what the "double square method" is: a Yorkshire square. Intriguing that this is likened to the Edinburgh system. Because, sure enough, there in Younger's records are the "beats" - beating the wort to rouse it. It had never occurred to me that this was the same concept as the continual rousing of a Yorkshire square. Which leads on to another question: what impact did this have on Scottish yeasts? Those used in Yorkshire squares had adapted itself to the constant rousing and wouldn't work well in a standard fermenter. Were Scottish yeasts the same?
Pontos (called pontoons here) I think we all know about. They are a forerunner of union sets, basically large casks from which the yeast is allowed to escape through the top. The difference with unions being that the casks were upright rather than on their sides and needed to be topped up manually. The troughs and pipes of a union set effectively automated the topping up process. William Younger had unions of their own. Though these, in imitation of Burton, were only used for their Pale Ales.
Amazing, isn't it, how much you can learn from three paragraphs of text.