This room houses the bottom of the grist case and this is the point at which the crushed grain or grist meets the brewing liquor. Mixing of the two occurs in the Steel's masher which is a copper cylinder containing mixing rods mounted on a centre spindle. As the porridge like mixture travels along the length of the masher, salts are added from the tank on the floor above.

The mash tuns are the original cast iron vessels but clad in stainless steel following leakage. The vessels have a false bottom consisting of a number of numbered gunmetal plates, numbered so that when taken up they can be replaced in the same position. The vessel is fitted with a sparge arm to flush sugars from the grain bed, and six wort outlets spaced around the base of the vessel. Hinged lids allow access to the vessels when necessary and help retain heat.

Mashing is a temperature critical process and so it is important to warm the vessel in order that heat is not lost. To achieve this, hot liquor is run into the mash tun via the sparge arm until the void under the plates is full and the water level above the plates is around one inch. At this point the grist is mixed with the hot liquor in the Steele's masher and drops into the mash tun. The liquor temperature is controlled around two degrees higher than that desired to compensate for the fact that the grist is cold. Once the grist case is empty the mash is left to stand for one hour. During this hour the enzymes which are active in the malt break down the starch into sugars and the sugary solution or Wort is run from the mash tun into the coppers. As the wort is run from the mash tun, hot liquor is sparged over the bed of grain to wash residual sugars from the crushed grain. The spent grain is still dug out by hand and sold as cattle food.