The mash tun is the brewing vessel in which grain is heated with water in order to convert the grain's starch to sugar. This process is known as mashing. The grain is then rinsed, or lautered, either in the mash tun or in a separate vessel known as a lauter tun.
In home brewing, the mash tun and lauter tun are generally combined into a single vessel, known as a mash/lauter tun and often created from a converted picnic cooler or keg.
 Creating a Picnic Cooler Mash Tun
 Creating a Keg Mash Tun
To create a mash tun out of a keg, two important pieces of equipment are required- insulation and a false bottom (like for any mash tun). A plasma cutter will make it easier to cut holes in the keg, since they are frequently made out of stainless steel.
Very important for any mash tun is its ability to maintain stable mash temperatures. Since stainless steel conducts heat very easily, insulation should be installed on the outside to prevent it from losing heat. Camping mats are the most common insulation- though any type of foam sheeting will work fine. It is normally secured to the mash tun using steel belts.
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