mash tun
An insulated vessel used in making the mashing process in which grains and water are mixed and heated to produce wort prior to fermentation.
mash tun: grain vessel where starch converts to sugar
A mash tun is an insulated cylindrical vessel, typically 50 to 500 liters in capacity, used in brewing and distilling to steep crushed grain in hot water. Its core function is to hold a mixture of malted barley (or other grains) and water at a stable temperature, usually between 62 and 72 degrees Celsius, for 60 to 90 minutes. During this rest period, enzymes naturally present in the malt break down starch into fermentable sugars and other compounds, creating wort that will later be separated from the spent grain.
The vessel itself is built from stainless steel or copper with thick insulation (foam or mineral wool) to minimize temperature loss. A perforated false bottom sits above the main drain, typically a ball valve or similar fixture. This false bottom prevents grain from clogging the outlet while allowing liquid to run off. Some mash tuns include a recirculation arm or rotating spray head to distribute water evenly across the grain bed during initial mixing and sparging.
Mashing regimes and efficiency
The quality of the resulting wort depends on maintaining precise temperature steps. A single infusion mash holds temperature constant; a step mash raises temperature in increments to activate different enzyme sets at different times. Brewers measure efficiency by how much sugar they extract from each kilogram of grain, typically targeting 65 to 80 percent depending on technique and grain type. Poor insulation, uneven heating, or grain bed channeling (water flowing through certain paths rather than the whole bed) all reduce extraction and consistency.
After mashing is complete, the brewer runs off the liquid and then sparges: sprinkling new water across the grain bed to rinse out remaining sugars. The grain bed itself acts as a filter, trapping particles that would otherwise cloud the wort. This is why a false bottom and controlled flow rate are essential, they prevent channeling and maintain clear separation.
Industrial breweries and distilleries often replace traditional mash tuns with lauter tuns (which add a rotating rake to mix grain and prevent compaction) or with mash filters that use compressed air or hydraulic pressure to squeeze liquid from grain. However, the mash tun remains standard in craft brewing and smaller operations because it is simple, reliable, and requires minimal power and maintenance beyond regular cleaning.