For the production of a fine beer, more depends upon boiling than brewers generally admit. There is more that should be considered than mere ebullition or mere attainment of 100° ; tbe influence of barometric pressure, shape of the copper, whether it is closed or open, are of great importance, but have not received that attention which experiment has shown them to merit. Tbe peculiar flavour of London porter is undoubtedly due to the particular method of boiling, and to the use of large boiling coppers. A column of water 2 ft 3 in. higb, gives a pressure of 1 lb. a square incb, and a temperature difference at the two extremities of about 1°, when heated as beers usually are, so that a boiler of 12 ft. in depth may have a difference of about 5° (8° F.) from tbe temperature of an ordinary beer copper. A wide copper, that allows freedorn to tbe currents of ebullition, keeps its wort cooler than a narrow copper, in which the upper and downward currents come into contact. For this reason a wide bulging copper, with an ascending current in the centre and descending currents at the side, is best fitted for pale beer ; and a deep copper with almost perpendicular sides, by constricting the space for circulation and causing the descending currents to return upon tbe ascending currents, in other words, the cold currents upon the hot, is best for porter. In boiling, any hindrance to circulation causes increase of temperature. The wort at tbe bottom of the copper, loses solidity, becomes frothy and thus loses its conducting power, so that the copper bottom attains a temperature which renders the copper bad for ale, but better for converting extract of black malt into porter. Boilers with steam tubes at tbe bottom, and a false bottom at some distance above the tubes, intended to keep tbe bop from contact with tbe source of beat, are unsuccessful, because there is no circulation, and the wort beneath the false bottom is superheated, whilst that above remains cold. In Scotch breweries, tbe coppers are much wider than they are deep, whilst in the West and North of England they are deeper than wide ; on this account Lancashire beer takes its peculiar flavour. The bigh temperature employed in boiling Lancashire beers is beneficial only so long as the malt is properly cured, and so dried as to approach an amber colour, but, without tbis preparation of the malt, it is useless to attempt rectification in the copper. It is agreed in tbe best practice that extra heat in the copper will not give additional keeping quality to either blaok or pale beers, unless the malt bas been cured and heated to correspond with tbe temperatures of the coppers. Narrow coppers are wasteful and troublesome, because the contents are liable to be forced over the lips from tbe want of space for the currents of ebullition. Scotland and Lancashire may be regarded as presenting examples of the extreme limits of form for coppers. In London breweries, domed coppers are employed, and this may in some measure account for the superior flavour of London porter. Porter must be boiled at a temperature of 107° to 110° (225° to 230° F.), and this temperature can be attained in a straight-sided boiler, well fired, by boiling at a charge depth of 12 ft., or with a pressure in a small domed-boiler of 4 or 5 lb. a square inch. Domed coppers, besides the safety valve have a vacuum valve to prevent collapse ; steam boiling is attended with some diffi culty unless carried out in double-bottom coppers, which require tbe use of tubes to give 50 per cent. of steam surface over that of fire surface.
Graham is of opinion that long boiling is necessary, and that a portion of the quantity of hops slaould be added after the first half-hour's boiling, the scum removed, hops again added, and boiling continued for an hour or an hour and a half, as may be required.
All beers when kept for a few months, age and lose the distinctive flavour of the hop. In the hopping of beers, the range of quantity between 4 to 24 lb. a quarter occurs in practice. Scotch mild ale is made with 4 to 6 lb. to the quarter, and Scotch pale ale with 10 lb. of bop ; Burton mild ale, 12 lb. ; Scotch export ale, 16 to 20 lb. ; Burton home pale ale, 20 to 21 lb. Porter, for early sale, is made with 8 to 10 lb. of bop, and for export, with 12 to 11 lb. good quality. Stout for home use is bopped with 12 to 11 lb. ; and export stout 16 to 18 lb. a quarter. The hop for porter and stout is always reboiled.
In raw bopping tbe beer in cask, 1 lb. to the barrel is usually allowed for home sales, and 2 lb. to the hogshead for export beers. The finest new bop is selected for this purpose ; delicate for home, and strong for extract beer. Vatted ales are always raw hopped. Stouts are sometimes thus treated, according to the prsctice of the brewer. In the best practice, it is generally admitted to be a mistake to bop the beer both in copper and cask, especially for the purpose of correcting stale malt ; a better plan is to re-dry the malt.
the introdnction of refrigerating apparatus, beer wort was cooled on cooling floora, flats of buildinga floored and flanged round t,o a depth of about 6 in. These floors were of oak, teak, cast iron, or copper, but the losa of beer from the old wooden coolers through absorption by the wood was sometimes equal to 5 per cent. of the net results of the brewing. Con,siderable difference of opinion occurs as to the advantages of refrigerators over coolers, but beyond the advan tage of evaporation, in helping to remove the mash water, there is no benefit from the use of a cooler. The moat economical and safest brewing is that conducted with refrigerators, so that the wort may be run direct from the hop-back through the refrigerator to the permeating tun. If
the refrigeration ia effected with cold water, the aupply necessary is equal to double that needed to cool with the cooler, if the wort is at a temperature when it begins to run, of about 55° (130° F.).
After boiling, the worts are, as a rule, discharged from the copper or boiling back, as the case may be, into the hop-back, a large tank or vessel fitted with strainers for separating the hop from the wort. In those breweries in which the wort has to be pumped from the hop-back into the coolers, the former, in addition to acting as a strainer, serves as a reservoir from which the pumps can draw. Sometimes the bops are pla,e,ed in the boiling back, enclosed in a perforated sheet-iron vessel, and aa in this case they cannot mix with the wort, the latter does not require to be strained after boiling, and it is therefore run direct from the boiling back to the coolers, no hop-back being used.
A hop-back should always be capable of containing the full e,ontents of the copper in connection with which it is worked, and if it is of any great size, it should be fitted with elevating machinery, for returning the hops to the copper. To enable hop-baoks to act as atrainers, they are fitted with perforated false hottoms, conatructed generally of cast-iron plates, arranged to be readily removed for cleaning purposea. The space below the false bottom communicates either with the auction pipe of the pumps, or with a pipe leading direct to the coolers. The perforations in the false bottoms are sometimes narrow slits about A in. in width, and 2 in. or 3 in. long, and sometimes small holes about * in. or A in. in diameter. In either case, the perforations are well countersunk on the inner side of the plates, so that the thickness, through which the narrow openings extend, is not great. The draining power of auy hop-back varies directly as the area of the openinga in the falao bottom, and, as them openings must not be limited iu size, they should be placed as closely together aa possible. As the flow of the wort through the perforations is accelerated by increasing the depth of wort, there has been an erroneous tendency to make hop-backe deeper than needful, to obtain increased head. With a given quantity of wort, an increased depth can only be obtained by a reduction of the horizontal, and consequently of the drainage, area, hop-backs, as a rule, being furniahed with perforations only at the bottom. The reduction of drainage area consequent upon the increase in depth varies directly aa that increase, whilst the velocity of flow through the perforations in the false bottom ia augmented only as the square root of the increase in depth. For example, a hop-back has a drainage area of 40 aq. ft., and the wort stands at a depth of 4 ft. above the false bottom. The theoretical velocity of flow through the perforations should be about 16 ft. a second. If the hop-back be supposed to be contracted until the horizontal area is reduced to 10 sq. ft., the depth of the wort will be increased to 16 ft., and the flow due to this head will be 32 ft. a second. The velocity of flow will only have been doubled, whilst the drainage area has been reduced to one fourth ; and the quantity of wort drained from the back in a given time will only be half that in the former case. The greater the depth, the greater also will be the quantity of hops deposited on each unit of area of the bottom, and the more resistance offered to the passage of the wort. When the depth of tbe wort above the false bottom is 5 ft. 9 in., there will be about one barrel above each square foot of bottom area, and the quantity of hops deposited a square foot will nearly corre spond to that quantity a barrel, whilst, if the depth is but 2 ft. 10/ in., there will be but half this quantity deposited a aquare foot, and so on. A certain portion of the drainage area can be kept clear by raking away the hops ; but the area covered by the hops will always depend upon the depth of wort originally contained in the back. Hop-backs should, therefore, not be more than 2 ft. 6 in. or 3 ft. deep above the false bottom. Where the wort is pumped from below the false bottom of a hop_ back, an artificial head is caused by the exhaustion, if the pumps are aufficiently powerful. In a. hop-back at Charrington's brewery another plan has been adopted, to avoid loss of drainage area by the deposit of hops. This hop-hack is provided with vertical grilles, in addition to the ordi nary perforated bottom. The back, 48 ft. long by 12 ft. wide and 5 ft. 3 in. deep, is provided, at a distance of 6 ft. from each end, with a diaphragm or partition. The partitions are each formed of a series of angle irona placed vertically side by side, with apaces* in. wide between. These vertical angle irons, forming the grids, are riveted at the top to an angle iron. Between the diaphragm s or screens, the hop-back is provided with a false bottom, placed 3 in. above the real bottom, and constructed of cast-iron plates. The cast-iron plates are each 3 ft. long by 1 ft. wide by Tg, in. thick round the edges, and * in. thick at the perforated portion. The holes are A in. in diameter, and are deeply countersunk on the under aide, and are placed at 1 in. pitch. The space between the false bottom communicates at each end with those portions of the hop-back beyond the vertical grilles, the end openings being each protected by a curved grill, formed of angle irons similar to those used in the vertical screens, hut placed closer together. The bottom of the back. is laid with a fall of 1; in. a foot from each end towards the centre, where a gutter, 3 ft. wide by 51 in. deep, is formed, with which the suction pipe of the pumps communicates.