Mashing technology is the process by which sweet wort is prepared. It involves ‘mashing in’, the mixing of the milled grist and the brewing liquor at the correct temperature and in the correct proportions to obtain the mash. After a period, with or without temperature changes, during which the necessary biochemical changes occur, the liquid ‘sweet wort’, which contains the extract, is separated from the residual solids, the ‘spent grains’ or ‘draff’.Some extract remains in the draff, and as much of this as possible is recovered by ‘sparging’, washing the grains with hot brewing liquor.
In traditional brewing, as practised in homes or small inns, hot water was placed in a wooden tub or tun, and the grist (malt that had been ground between millstones) was mixed and mashed in by stirring or rowing with a rake, paddle or ‘oar’. No reliable means of measuring temperatures was available. In one method, which gave rise to the ‘classical’ British infusion system, the water temperature was guessed to be suitable by feel or by how clearly the brewer’s face was reflected in the water. After a period a basket was pushed into the mash and wort that seeped into it was ladled into a receiver, in readiness for boiling with hops or other flavouring herbs.
When wort recovery became difficult more hot water was mixed into the mash (re-mashing) and another, weaker wort was recovered. This was repeated until the worts were too weak to be worth collecting. In later times wort was collected from mashes using primitive mash tuns, in which the wort drained from the mash through a perforated ‘strainer’ in the base of the tun. The structures of old , relatively small British country house breweries are documented .
In an alternative method, which gave rise to the classical mainland European decoction mashing system, traditionally used for brewing lager beers, the mash was made with slightly warm water. At intervals a ‘decoction’ was carried out, that is, a proportion of the mash, perhaps one-third, was withdrawn and slowly raised to boiling in the copper that would later be used for boiling the wort. The hot mash was then transferred back to the ‘main mash’, and was mixed in. In this way the temperature of the whole mash was increased. Repeated decoctions increased the mash temperature in steps, an approach that minimized the risk of overheating and premature total enzyme destruction.
In more modern variations of this system the temperatures achieved (now exactly controlled) are optimal for various enzyme-catalysed processes in the mash and allow comparatively under-modified malts to be mashed successfully . Raw cereal adjuncts may conveniently be cooked in decoction vessels. In contrast, the traditional infusion system of mashing requires well-modified malts and not more than about 20% of unmalted adjuncts.
The equipment used in breweries has been progressively refined and there has been a convergence in the practices of ale and lager brewers. The motives for these alterations are chiefly economic. It is often desirable to maximize productivity (‘throughput’, the number of brews completed every 24 h) and to recover as much extract as is economically worthwhile from a given grist . It is also necessary to reproducibly recover a certain volume of wort having exactly the characteristics needed to make a particular beer. At the same time energy and water usage must be minimized and so must the production of effluents. At the present time there are breweries operating with many different kinds of ‘traditional’ and ‘modern’ equipment.
The more common types will be described. Sometimes old types of plant have been retained, despite some inconvenience or poorer efficiency, because a newer system has not been able to produce a beer matching that produced by the old system. In the case of smaller breweries older kinds of equipment may be retained because of its simplicity, or because replacement is not economic. While older equipment is often made of attractive polished wood and copper, in newer equipment these materials have been largely replaced by the cheaper, more deterioration-resistant stainless steels.