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Malt Milling
Malt Dry Milling
The most commonly used mills in breweries are dry grist mills. Mills are usually either of the roller type or based on impact, i.e. hammer mills. If the wort separation process is a mash/lauter tun, roller mills are employed. Hammer mills are largely used for the later generation of mash filters and continuous brewing systems. However, new generation mash filters, for example, Meura 2001, require the use of hammer mills.
Roller Mills
The principle of roller milling involves passing the malt between two closely spaced rolls; roller mills can be of the two-, four-, or six-roll format. In general, the more rolls, the greater the flexibility and capacity of the mill. Multi-roll malt mills provide a degree of control that favors gentle treatment. The grind is controlled by the rate of the feed of the unground malt, the roll corrugations and size, the spacing between the rolls, and the speed at which the rolls are driven.
Hammer Mills
A hammer mill (see Figure 8.5) consists of a rotor made of two or more plates with pins to carry the hammers. Hammers are simply flat metal bars with a hole at one or both ends. They may have some type of edge preparation such as hard facing or carbide coating to provide better wear resistance. Reduction in a hammer mill is primarily a result of impact between the hammer and particles, or between particles and screen when the material accelerated by the rotor flies out into the screen.
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