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Insulated Keg/Mash Tun

Right now I’m doing 5gal all grain batches using a Rubbermaid/Gott insulated water cooler for my mash tun. It works great but does have some drawbacks:

  1. It works great for low, medium, and some high gravity batches, but if you want to do a really high gravity brew, like a barley wine, the grain bill and water required may come very close to exceeding the capacity of the cooler.
  2. Being plastic, and not really made to hold hot water that above 140 degrees, the inner plastic has a tendency to warp after a while, especially if you pre-heat the tun with very hot or boiling water prior to pumping in your strike water. It’s also problematic if you are using a false bottom, and the plastic warps to an extent that it allows grain to slip past and clog your dip tube.
  3. Since I use a dip tube and ball valve assembly to drain the wort out of the cooler, the warping of the bottom from the heat makes it difficult to get all of the wort out without tipping the container. I often have several quarts of wert left in this “deadspace”.
  4. Finally you are limited to 5gal or at most 6gal batches.

If moving up to 10gal batches is a goal, many homebrewers either buy a dedicated mash tun, or convert a stainless steel beer keg to a mash tun. Only problem is that if the tum is not well insulated, there has to be some way of keeping the mash at the proper temperature. Since stainless steel is an excellent conductor of heat, some way must be found to insulate the keg/tun.

Many homebrewers use reflectix insulation wrapped around the tun, others use blankets, and still others use direct-fired or recirculating heater system to keep the mash at the proper temperature.

My approach is to use a decommissioned rubber-coated keg that I found on Craigslist. After releasing any pressure in the keg, I removed the keg spear. I then turned the keg upside down, and using a combination of an angle grinder, sawsall, and dremel rotary tool, removed an approximately 11″ circle from the bottom of the keg. This is a messy job, and if you undertake it I highly recommend hand, ear, eye and breathing protection, as there are sparks, steel splinters, and rubber dust flying everywhere. This was my first attempt using the angle grinder and sawsall on a combination of rubber and steel, so the result isn’t perfect, but certainly good enough. I also deburred the sharp edges of the opening with sandpaper. The 12″ lid from my original 5gal kettle also happens to be a perfect fit.

Here is the uncut keg
This is the keg with the cutouts
The keg opening
A closeup of the keg opening, showing my “whoopsie” with the sawsall.

The reason I cut out the bottom of the keg instead of the top is to used the already domed portion of the top of the keg, along with the sanke fitting, to make a bottom-feeding drain. This is accomplished with a 1/2″ coupler, some stainless steel pipe, and a ball valve. This greatly reduces deadspace, and ensures that almost all of the wort is drained from the tun.

More photos as I progress…

Update: 03/02/2012

Did a little more work, and got some parts in…

Cut some more of the rubber away.
I hope to enlarge the opening and clean it up a little
Added the drain hardware to the bottom of the tun

Unfortunately, the 13″ stainless steel false bottom I have for my 10gal Rubbermaid cooler is too large to get through the opening of my mash tun, so I’ll prebably be ordering a new hinged false bottom from NorCal Brewing Solutions sometime soon. In the meantime, I’ll check for leaks and wait…

Update: 03/10/2012

I got my folding false bottom from NorCal Brewing Solutions, and built a small stand out of some 2x4s. Put everything together, filled it with water, with nary a leak.

Folding False Bottom (thanks JayBird!!) Wooden stand for Mash Tun

Update: 03/17/2012

OK, yesterday I filled the tun with about 13gal of 180 degree water, put a lid on top, and took temperature readings every 10 minutes for an hour and a half. The results were not good. Ambient temp was 68, with gusty winds. There was an almost linear 3 degree drop at every reading.

I’ve already started gathering what I need for a RIMS setup, and I’m going to get some reflectix.

Update: 03/24/2012

I picked up a 24″x25′ roll of reflectix insulation and some metal tape from Home Depot, and wrapped three layers around the tun. I also insulated the lid:

Relectix-wrapped Insulated lid

I didn’t have time to run any temperature tests, as I was also making a keggle, so that will have to wait.

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