The Oxford Companion to Beer definition of
Developed and patented in England in 1853, Steel’s Masher is a device to hydrate the grist, eliminate manual mixing of the mash with paddles or oars, and optimize temperature control during mash-ins. Designed specifically for use in infusion mashing schemes with single temperature rest, a Steel’s Masher is a critical piece of equipment that allows the brewer to control both the malt flow (via a slide valve) and the mash water flow into the grain to maintain consistent temperature throughout the mash and obtain excellent wetting and mixing.
During the mash-in process, grist (milled malt) is fed into the top of the Steel’s Masher, and makes a right angle turn into a horizontal feed auger. Mash water is supplied either before or at the feed auger, then the mixture transfers through a series of mixing paddles or mixing rods where the malt is thoroughly mixed with the water. By the time the grain exits the masher, it is completely wetted. The mash then is then fed to the mash tun. This is called “doughing in.” Modern Steel’s Mashers are equipped with sophisticated temperature sensors and water mixing valves that allow precise temperature control of the mash as it enters the mash tun.
Versions of the Steel’s Masher remain in use in many English ale breweries and in some American craft breweries.