How to Convert a Keg to a Mash Tun

Written by jacob andrew
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How to Convert a Keg to a Mash Tun
Old sankey-style beer kegs can often be acquired from distributors and brewers relatively inexpensively. (Jupiterimages/ Images)

Mash tuns are used to extract the sugars necessary to create beer from barley. A quality mash tun can be created from a variety items, including insulated coolers and used beer kegs. To best extract malt from the mash, milled barley mixed with water, must be brought to a different temperature and held there for a period of time. Keg and other metal-based mash tuns provide the benefit of allowing a burner to be mounted directly beneath, facilitating a more precise control of mash temperature than merely adding boiling water.

Skill level:

Things you need

  • Empty beer keg
  • Dremel or other metal-cutting tool
  • Adjustable wrench or wrench set
  • 3/8-inch OD threaded copper coupler
  • 3/8-inch copper hex nut
  • 3/8-inch ID sterile rubber gaskets
  • 3/8-inch copper ball valve with 3/8-inch barbed connector
  • Mash manifold

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  1. 1

    Cut a hole in the top of the keg. Ensure it is large enough to easily accommodate the dumping of loose grain, but small enough to help maintain some of its heat. Twelve inches in diameter is a reasonable size.

  2. 2

    Measure and cut a 3/8-inch hole roughly 3 inches to 6 inches from the bottom of the keg.

  3. 3

    Insert the threaded coupler into the newly cut hole.

  4. 4

    Secure the coupler by placing gaskets on the inside and outside of the keg. Follow this with a copper hex nut screwed onto the inside and the outside. The gaskets should create a tight, liquid-proof seal.

  5. 5

    Screw the ball valve onto the end of the coupler outside of the keg. This will allow for the tightly controlled extraction of the wort (unfermented barley sugar water).

  6. 6

    Attach the manifold (or false bottom) to the side of the coupler on the inside of the keg.

Tips and warnings

  • There are many variations on manifold and coupler assemblies. Some prefer to have pipes with threaded connections welded to the inside and outside of the keg instead of using gaskets, which creates a more watertight seal, but requires access to welding devices or services. Manifolds made of copper tubing are relatively cheap and easy to make, but simpler solutions can be devised from the metal mesh of washing machine hoses. Ultimately, the manifold must simply allow for liquid to pass out of the coupler without allowing barley husks or other solids through. Piping with a 3/8-inch outside diameter is commonly used for home brewers' mash tuns, but you can use larger or smaller piping at your discretion. Ensure the coupler has threading all across it. The gaskets and hex nuts need to be able to be screwed all the way to the wall of the keg. Consider adding additional features to the keg mash tun, including a thermometer or depth gauge. These are usually sold in kits from home brew stores and only require you to cut additional holes in the keg.
  • Remember that everything inside the couple and the keg is going to be used for human consumption. Do not use manifolds, piping or gaskets that are treated with chemicals proven harmful to humans. Be sure to test the watertight seal with a few gallons of hot water before using the mash tun. A leaking tun can easily be remedied with better gaskets or a further tightening the locknuts, but not if there is 4.54kg. of grain and gallons of water in the keg. Thoroughly clean the inside of the mash tun before first use, as metal shavings and other detritus can result from the cutting and shaping.

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