It is the custom to complete the length, or total quantity, of a brewing by distributing over the goods the required amount of liquor by the aid of a sperger. A sparger in its usual fnrm consiste of two or more tubular radial arms, perforated on one side, and leading from a central cistern. These arms are mounted to revolve freely over the goods in the mash tun. In some cases, the cistern rests upon a point, and in others it is carried by friction wheels. When the mash tnn contains mashing apparatus driven from the central shaft, the cistern of the aparger is made annular to surround the shaft. The shaft carries a. disc, on which run the friction wheels of the sparger ; in many instances the bevel wheel on the shaft serves as brace for the friction wheel. The cistern ia in most cases open at the top, the liquor being delivered into it by a pipe conveniently placed ; but in some instances the vessel is connected to tbe supply pipe by a. joint, so that the water may be delivered under pressure, the joint being formed so as not to interfere with the reaction of the sparger. Spargers are chiefly driven by reaction, the water issuing from the perforations of the arme, im parting motion to them on the principle of Barker's mill. But spargers are sometimes driven from the shafting by a light belt or cord, with the object of ensuring regularity of motion, and con sequently equal distribution of the liquor over all parte of the goods ; but if a self-acting sparger ia well constructed, the irregularity of its motion must be extremely small.
A point of far more importance than any slight irregularity of motion is tbe proper distribution of the holes in the arms of a sparger. In order that the liquor may be equally distributed over all parts of the goods, it is necessary that the quantities of water delivered from different points in the arms should be iu exact proportion to the areas swept over by those points. If the first hole in the arm of a sparger ie 6 in. from the centre, and the last hole distant 6 ft. from the same point, the latter hole will, FIB the eparger revolves, cover a circle twelve times Ete great as the former, and in order that the goods passed over by the two holes should be equally wetted, the delivery of water from the outer hole should be twelve times that from the inner. The required increase in the delivery from the outer ends of the arms may be obtained either by increasing the size of the holes, or by placing them nearer together as they are farther from the centre, or by combining these two methods. The sparger arme are sometimes straight and sometimes curved, the object of the curving being to cause the water to tend outwards in radial lines. The curvature to be given depends upon the speed at which the aparger revolves and the rate of flow. If the arma be formed of tubes of the same diameter throughout, the flow will be most rapid near the centre, the rate of flow at any point being approximately proportionate to the area of the discharging holes beyond that point. The best practice is to taper the arms gradually outwards, observing that the sectional area at any given point is at least equal to the combined area of the discharging holes beyond that point. If the taper of
the arme be properly proportioned, the rate of flow will be constant at all points. Whether the arms are curved or straight will then make but little practical difference, so long as the spargcr revolves at the usual moderate speed.
The next apparatus in the order of use is the uuderback, which receives the wort from the mash tun. In some breweries, the wort is run direct into the coppers. The unclerback is a necessity where the coppers are situate at a higher level than the mash tune. Underbacks Etre of various shapes and materials, chiefly wood, and rectangular. A circular form is better, as it is more easily kept clean.
When cast iron is used it should be lagged with felt and wood, unless the wort can be very rapidly raised into the coppers, or unless the underback is fitted with steam pipes, so that the temperature of the wort may be maintained.
The underback should be situate so that the taps through which the wort is discharged are in full view. In drawing off the wort, the taps are at first partially opened, being more fully opened when the wort runs off clear. The wort is generally drawn from four or more points in each mash tun, and in the event of any tap not delivering clear wort, it is shut off for a time. The appearance of the wort will vary according to the kind of malt used. The wort drawn from the first mash should closely resemble in colour the mixture of malt used, and it should have a close and tough, silvery white head, changing to a delicate cream colour. The temperature or tap-heat at which the wort is drawn varies according t,o the nature of the malt used ; but it is about 62° to 63° (l44° to 146° F.). If the heat of the mash be too high, the head on the wort will have a brown tinge; and if too low, the head will be deficient in closeness and firmness, and the wort will not he bright or well flavoured. Wort of this kind is particularly liable to acetification, and it should be exposed to the air as little as possible. Wort of any kind is not benefited by exposure at this stage, and should never be allowed to remain in the underback longer than is necessary.
When the wort has been drained into the underback, the mash tun is cleared of the waste malt or grains. This is ordinarily done by men with wooden shovels, but involves waste of labour in large and deep tuns. A better method is to provide the tuns with openings in the side near the bottom, communicating with shoots. The wort when drawn frorn the mash tun is composed of water, glucose or saccharum, and gum or mucilage, together with small proportions of starch, gluten, and albumen. During the early part of the process of boiling, diastase effects the conversion of the starch into sugar, dextrine, and gum ; and as the boiling goes on, the wort is concentrated, and a certain proportion of the albuminous matter present is deposited in a flocculent form. The hops are added to the worts at this stage.