Hammer Mill is one of several mill types employed in the brewhouse for crushing whole grain kernels—malted and/or unmalted, depending on the beer recipe—in preparation for mashing and lautering. Other designs are wet and dry roller mills. See dry milling, lautering, mashing, milling, and wet milling. Whereas most mills do not grind the grist to a flour-like fine powder, hammer mills are specifically designed to achieve a perfectly fine grind. In theory, the finer the grind, the easier it is for grain enzymes in the mash to access the grain starches for the purpose of converting them to wort sugars. It also improves proteolysis, which can be important in the case of undermodified malt. See modification and proteolysis. In practice, however, fine grinds tend to clump in the mash and make the mash too doughy for mash water to flush out the sugars that are produced. Instead, the sugars get trapped. For this reason, hammer mills can be used only in brewhouses that employ a mash filter instead of a conventional lauter tun. See mash filter. The construction of a hammer mill consists of a round, usually horizontal, metal housing. The top of the housing has an opening for the kernels to enter, whereas the bottom half of the housing is perforated and serves as a screening sieve. A spindle is centrally mounted inside the housing. On it are fixed one or more perpendicular disks and from the periphery of each disk protrude many fix-mounted or pivoting flat vanes, bars, pins, or “hammers.” Depending on the shape of the hammer, the mill may also be called a pin mill. As the spindle and the disks rotate, the hammers smash the kernels to bits until they are pulverized and fall through the screen, from where they are sent to the mash. There are also vertical hammer mill designs, which operate on the same principle. If used in conjunction with a mash filter, hammer mills yield the most economical wort extraction, but they also add more beta-glucans to the wort, which may cause beer filtration problems later on.

See also beta-glucans and filtration.