Yorkshire beer has long held a fine reputation for its quality, well beyond the boundaries of the country. Historically, this may in no small part be due to the almost unique use by the county’s brewers of the Yorkshire Stone Square method of fermentation; a system which only spread to a very limited extent to the counties of Lancashire and Nottinghamshire, but not, seemingly, elsewhere.
The method adopted almost universally throughout the rest of the country is known as the skimming system. In this system, the head of yeast formed during the beer’s fermentation is skimmed off its surface into outlets at the side of the fermentation vessels.
The only other truly regional fermentation system is the Burton Union System, in which the fermentation takes place in long rows of interconnected casks, known as Unions. The particular suitability of the Union System to the production of pale and strong ales led to its almost complete adoption by the brewers of Burton-on-Trent, though brewers from other areas may have shared in contributing to its ultimate high level of development.
Two sources attribute the invention of the "stone square" system of brewing to Timothy Bentley of the Lockwood Brewery near Huddersfield: in a brief history of Bentley & Shaw Ltd., the company founded by Timothy Bentley, and a history of Bentley’s Yorkshire Breweries Ltd., founded by one of his sons, Henry Bentley. The Lockwood Brewery history also suggests that Timothy Bentley was acquainted with Doctor Joseph Priestley, or had at least made full use of the scientist’s work relating to the brewing industry. Sigsworth, in considering the possibility of a collaboration between the two men concerning the development of the stone square system, states that there is a close resemblance between the experiments conducted by Priestley and the principles upon which the stone square system works, in particular the impregnation of the beer with carbon dioxide. He concludes that the work conducted by Priestley whilst living close to the Meadow Lane Brewery of Jacques and Co., Leeds, is adequately substantiated, but that the Bentleys’ connection with the scientist is attested only by the reference in the two advertising brochures, published at least a century later.
The yeast used in the Yorkshire system is unusual in that it acts particularly slowly and requires frequent rousing and aerating if it is to work properly. This action is due in part to the yeast’s strongly top-fermenting qualities, which cause it to rise rapidly to the surface of the fermenting wort and thereby reduce its ability to perform its task of converting sugar into alcohol and carbon dioxide. The beers produced by the system, however, "drink very full for their gravities, and which, since they retain large quantities of carbon dioxide, are full of life." The effervescent nature of the beers brewed by the stone square system help to protect them from airborne infection during fermentation; it may also offer an explanation for another, peculiarly Yorkshire tradition, that of dispensing beer by means of handpumps fitted with autovac equipment, utilizing a very tight sparkle. The agitating action of the handpump displaces much of the dissolved carbon dioxide gas and at the same time introduces air into the beer. It is the air which produces the smooth texture to the beer and supports the long lasting, creamy head, so beloved of all serious beer drinkers in the Yorkshire area.
The stone square is so called because the fermentation vessels themselves were once constructed from large slabs of hard local stone, such as were the products of the quarries of the Elland flagstones. This type of stone is, even today, much prized as a paving material for the streets of London. The square consists of four large slabs of stone for the sides and a fifth for the base, all being fastened together by means of recesses cut into the stone and secured laterally by iron bolts. A second square, about three or four inches less in height, is constructed so as to surround the first, leaving a narrow gap of about two inches all round the external surface of the first square. Into this space either warm or cold water can be introduced thereby acting as an attemperator; surplus water simply flowing away over the top.
Above the inner square is placed another horizontal slab surmounted by a second chamber; of the same area as the outer square beneath, about thirty inches deep and constructed in a similar manner. In the centre of the base of the upper chamber (which acts as a yeast trough) there is a man hole of eighteen inches diameter, surrounded by a stone collar of about six inches in height, into which fits a stone lid with a handle. Close to one of the corners of the covering slab are located two valves of about three inches diameter to which chains are attached. A long pipe extends beneath one of the valves to within a few inches of the bottom of the lower chamber; it is known as the "organ-pipe." The whole massive weight of the structure is carried on large stone pillars, and the chambers themselves are rendered watertight by the application of water resistant cement to all the joints. An additional item required for the use of stone squares is a simple pump of three inches diameter and six inch stroke, which is used to pump wort from the lower to the upper chamber.
W.J. Sykes, in his book the Principles and Practice of Brewing, gives the following description of the operation of the Yorkshire stone square: The wort is pitched with one to twelve pounds of yeast per barrel at a temperature of 58 to 59 degrees Fahrenheit. The valve at the upper end of the organ-pipe is closed and a portion of the wort run into the upper chamber; the yeast is then thoroughly roused (vigorously mixed) in with this, the valve opened, and the mixed yeast and wort allowed to flow into the lower chamber. When the whole of the wort has been collected and pitched, it is left undisturbed for 36 hours, at the end of which it should have risen to about 62 degrees Fahrenheit. It is now roused for the first time, the rousing being repeated every two hours during the next twelve hours, at the expiration of which (48 hours after pitching), pumping commences. Before starting the pump, the valve of the organ-pipe is shut and as much wort is dumped into the upper chamber as is delivered by fifteen strokes of the pump; it is then well roused, so as to mix in the yeast which has risen through the man hole, after which the valve is opened and the wort allowed to flow back into the lower chamber. Pumping and rousing are repeated every two hours, the number of strokes of the pump being increased at each repetition of the operations, beginning with fifteen strokes for the first pumping, and increasing by ten at each pumping. This is continued until the wort has reached a gravity of some 1 to 11 degrees higher than that required to finish.
During the whole period of fermentation the temperature of the wort is kept within the necessary limits by means of the attemperating jacket. When the pumping and rousing stage is passed the organ-pipe valve is closed and the yeast which rises through the man hole removed every four hours. After each removal the valve is opened for a short time to allow the beer which has drained from the yeast to run down into the lower compartment. When, by observing the surface of the beer, the yeast appears fully removed, the temperature of the beer is gradually brought down by attemperating to 60 degrees Fahrenheit, or a little lower. The man hole is then covered with the cap, and the contents of the square allowed to remain undisturbed for two days, by which time the beer is ready for racking into trade casks.
Stone squares of the type described above, were probably in use from the latter years of the eighteenth century and were well established by the 1830s. A lease taken out by Samuel Webster in May 1838 describes the working room of the Fountain Head Brewery as containing three double cisterns, with a cistern on top of each to hold yeast, three large cocks and pipes for water. By the beginning of the present century, slate began to replace stone as the material for construction of squares, an internal attemperator being used instead of a surrounding water jacket. By the 1920s, although very expensive, aluminum began to be introduced for the construction of fermenting vessels.
The new material was much easier to keep clean and maintain than either stone or slate, and it did not suffer from the same restrictions in dimensions. With the new material came changes in the design of the squares, the upper yeast chamber disappearing on the grounds of cost and easier cleaning. Many breweries, however, continued to rouse and aerate their beers as had been done with the stone square system, but the yeast trough was replaced by the more commonplace skimming system. One of the last remaining users of Yorkshire squares, though of slate construction, are Samuel Smith of Tadcaster who pride themselves on the traditional nature of their brewing techniques. Near neighbours, John Smith, have retained a single stone square, along with its ancillary equipment, which is on display in a museum type gallery in their new brewhouse, formerly the square room.
One or two sets of stone squares have survived on the sites of former breweries in a derelict state, no doubt owing to the expense and difficulty of removing them, and await the attentions of brewery and industrial historians.