Another method of conducting fermentation is that known as the "Burton union system." In 1838, P. Walker, of Warrington, invented the method of cleansing beers, this method having for its object the superseding of the necessity which then existed for supplying by power or hand labour the place of the liquor discharged during fer mentation, to keep the casks full ; and to prevent the yeasty head from being broken in upon the wort. Ac,cording to his plan, independent passages vvere afforded for the flowing off of the yeast, and for the downward current of liquor, by which the cask or vessel was tilled up. Another advantage was that the liquor for filling up could be intro duced at the lower part of the cask, the yeasty head being left unbroken, and the attenuation allowed to go on in a regular and uniform manner.
Fig. 307 is a transverse section of such an apparatus applied to casks ; a is a conical tube inserted in tho bunghole of a cask ; from the upper part of this tube there rises the tube b, termed the yeast tube, so that the yeast as it rises may be delivered into the trough 0. A tube d de scends through the conical piece a, nearly to tho bottom of the cask, and this tube is at its upper end connected with a branch pipe which commu nicates with the trough at the bottom. These tubes are the Mug tubes, and by them the essks are filled and are kept supplied with liquor from tho trough e, to compensate the loss of that thrown off during fermentation. The joint-piece by which the branch p'pe is connected to the trough, is constructed with a plug like an ordinary cock, so that when the blanch pipe is disconnected it can be turned downwards, and the flow of liquor shut off.
The trough, which may be of any length required, is here shown suspended, whilst the casks are arranged on each side on sunk stillions. The malt liquor, in a sufficiently advanced state of fermentation, is run into the trough, from which it flows into the casks through the filling pipes, enough liquor being supplied to fill the casks, and to leave a certain quantity at the bottom of the trough. Tbe liquor thus left, together with that which is carried off with the yeast and which subsides in the trough, serves to make up the loss during cleansing. The yeast, as already stated, rises up through the tubes b, and flows into the trough c, and the fermentation and cleansing thus go on without attention until the completion of the operation, which is indicated by the yeast no longer flowing from the tubes.
The system of fermentation followed at Burton somewhat resembles both the Scotch and the London systems, but differs from both. In the Burton system, as in the Scotch, the fermenting tuns are of moderate size, from 20 t,o 100 barrels ; instead of the fermentation being essentially a slow one, the wort is stimulated with large quantities of yeast, and the same result brought about as is caused by the great bulk of beer fermented in a single tun at the London breweries. The Burton, like the London brewer, after the fermentation has proceeded for a certain time, finds it desirable to divide out the beer, the usual course being to distribute it amongst the requisite number of union casks, in which the cleansing. takes place. On the Burton system, the wort is
pitched at a low temperature, say about 13° or 14° (55° to 57° F.), and receives a liberal allowance of yeast, of 4 lb. to 5 lb. or even more a barrel. For the best ales the original gravity of the wort is about 22 lb. or 23 lb. a barrel, and the attenuation is allowed to proceed until the gravity is reduced to 4 lb. or 5 lb. No yeast is removed from the ale whilst in the fermenting tuns, the cleansing being performed entirely in the union casks ; in these the ale remains about a week before beiug discharged into the settling tanks. The fermenting tuns at the Burton breweries are in all cases of wood, and are fitted with attemperators. The tuns as a rule contain a greater depth of wort than those used in the Scotch brevveries. At a number of the establishments at Burton, open wooden troughs are employed. instead of pipes to distribute the wort to the fermenting tuns. At Bass's, tbe fermenting squarea are disposed in double rows, down each of which a pipe is led ; and from these pipes the squares are filled by the aid of open wooden trough.s. At the Burton brewery, the fermenting rounds of working capacity of 40 barrels are placed in. groups of eight, and are filled from movable wooden troughs, which receive the wort from a main trough situated round the walls of the tun room. Each movable trough extends across four tune, and these are filled simultaneously through holes in the bottom of the trough ; the holes are fitted with plugs so that the wort can be shut off from any tun. Similar open troughs slung from the ceiling are also used at many of the Burton breweries to distribute the fermented wort from the tuns to the troughs of the union casks. The advantages of open wooden troughs as a means of dis tributing the wort, are, that they are less in first oast than pipes, and may be kept thoroughly clean. They are, however, cumbrous, and are only applicable when the wort is supplied from higher level than 'the tuns. Union casks have generally a capacity of four barrels, and instead of being placed on the ground, as previously described, are slung on axles resting in bearings carried by a strong wooden frame. 'Usually the casks are disposed in double rows, each frame supporting from twelve to twenty casks. Above the oasks is plaoed the yeast trough. When the casks are thus mounted, the method of employment is as follows :—The ale to be cleansed is pumped, or run, into the yeast trough above the casks, and the plugs which close the pipes leading from the bottom of this trough being removed, the liquor runs down into the casks. When these are filled, the plugs are inserted, and the swan necks are thus left as the sole vents through which the yeast can escape.