The brewer uses as his primary raw materials malted barley (malt), water (liquor) and hops. Mashing involves the intimate mixing of ground malt with hot water to produce an aqueous extract of the malt called "wort" or "sweet wort". There are several methods of mashing. In an infusion mashing system, the mash is typically held at 65.degree. C. for a period of between 30 minutes to several hours. During this periods, enzymes of the malt attack principally starch and its degradation products (this is referred to as amylolysis). The production of wort takes place in a vessel, called a mash tun, which has a slotted base which acts like a sieve. In order to to wash virtually all the sweet wort from the undergraded material, hot water at 70.degree.-79.degree. C. is sprayed over the surface of the mash and the wort is allowed to drain out of the solids of the mash bed. Hence, both the mashing and wort separation are achieved within the same unit.
In the other available systems of wort preparation, the mashing is carried out, with stirring, in a jacketed vessel in which the mash temperature can be progressively increased to the required maximum value. For example, in the production of a lager beer, mashing might comprise (i) 40 minutes at 50.degree. C., (ii) 35 minutes to reach 65.degree. C., (iii) 45 minutes at 65.degree. C., (iv) 20 minutes to reach 75.degree. C. (see Spillane, M. H., Brewer's Guardian, 1978, 4, 63). In these plants, the mash is transferred to a wort separation (otherwise called "lautering") stage. The lautering systems which are now in use include: Lauter Tun, Strain Master or Mash Filter. Another system which is at the industrial assessment stage is the High Pressure Mash Filter.
In all these separation systems, separation of the wort is achieved by using a bed of the malted grain itself as the filter medium. There is in such systems a basic incompatibility between filtration rate and extraction efficiency (see Royston, M. G., J. Inst. Brewing, 1966, 77, 351). The rate of filtration increases as the particle size is increased and the bed depth is decreased, but the amount of soluble extract recovered from the grain will tend to increase as the particle size decreases and the bed depth increases. Prediction of system performance is difficult. System design is based on empirical procedures. Experience teaches that precise limits must be adhered to with respect to malt quality, the method of milling of the malt and the method of operation used during wort separation. Constant operator attention is essential in order to avoid worts which are cloudy and mashes which become set.
An increase in the percentage conversion of starch into fermentable sugars during mashing could be achieved if a finer grind of malt flour were to be used. An increase in the percentage recovery of soluble extract would lead to large savings in production costs. There is, however, a limit in the fine milling of malt beyond which the present systems become inoperable.
It is one object of the present invention to provide a separation system which functions efficiently with finer grinds of malt flour than are acceptable for the above-mentioned separation systems.
The presence of husk particles in the mash is essential for the present wort separation systems to be made operational. The husks allow the permeation of wort or sparge liquor (water) through the mash bed. Without this, the mash would be likely to set. Recovery of the soluble extract from the mash bed is achieved by (a) displacement of the strong wort with hot liquor (water) and (b) cake washing (sparging). The sparging step should extract the wort residing within the voids of the mash bed and within the solid particles. Since husk particles are cellulosic in nature the mass transfer of soluble extract from within those particles will be diffusion limited. Hence the presence of the husk particles limits the rate of separation of wort from the mash.
It is another object of the present inventions to avoid the need for husk particles to be present in the mash.
Present demands on the brewing industry suggest that the cost of raw materials will continue to increase and the market will require an ever wider range of beers. The first factor imposes a demand that the brewer works with a greater variety of feedstocks. The second factor requires the use of equipment which can perform satisfactorily at reduced load capacity. Feedstock characteristics depend on, for example, year to year variations in barley varieties, changes in the degree of malt modification, increases in the amount of unmalted materials added to the grist, and the use of non-traditional materials such as wheat malt and sorghum malt. It is another object of the present invention to go some way at least towards meeting these demands.
Apparatus for liquid-solid separation with continuous mashing systems has from time to time been proposed. These proposals include: a vacuum drum filter (see U.S. Pat. No. 2,127,759 (1938); batteries of centrifuges (see Williamson, A. G. and Brady, J. T., Tech. Q. Master Brewers Assoc., Am., 1965, 2, 79); cyclones and vibrating-screens.
Despite their deficiencies, the existing systems, in which filtering is through the grain bed, are still the methods of choice.
One of the main areas of recent efforts to optimize wort separation is improvements in the milling of the malt to provide a grain filter bed with a more easily reproducible and predictable filtering performance. For example, wet-milling can provide an efficient bed of essentially whole empty grain husks. With dry-milling, filter performance improves if the particle size of the broken husks can be kept more uniform.
For most brewers, the Lauter Tun is still the preferred equipment for wort separation. Improvements in its performance are currently being sought by careful attention to the design detail of the raking and sparging equipment of the Lauter Tun.