Building a 10-Gallon Mash Tun

Looking to build an inexpensive and effective mash tun? Look no further, and read on!

Please note: All specific parts listed here are fitted for a 10-gallon Igloo beverage cooler. If you have a Rubbermaid or other brand of cooler you may need to adjust the size of the fittings to cooler but the same principles apply.

One of the most important pieces equipment in a brewery is the mash tun, the large vat which extracts the fermentable sugars and tasty deliciousness from crushed grains. In the case of homebrewing, we perform essentially the same step when we steep specialty grains, perform a partial mash, or when we move to an all-grain setup. This requires that we hold our mash at a constant temperature for a period of time – usually 60 minutes if we are dealing with grains that produce fermentable sugars. This can be a tricky task when dealing with larger volumes of water. Sure, kitchen elements and propane burners provide heat but these heat sources can be difficult to dial in to yield that desired constant temperature over an extended timeframe. And really, who really wants to sit and babysit a pot and thermometer for an hour longer than they need to?

Instead of applying constant heat, many homebrewers have turned to a solution to keep the heat inside rather than pull it from the outside. Enter the insulated beverage cooler. Available in varying sizes, these can be converted into an ideal mash tun with a little DIY handiwork. Last week I converted a cooler with great results – I was able to mash my grains and only lose exactly 1 degree Fahrenheit over the course of the hour, well within the accepted range.

To make a mash tun:

1. Obtain a beverage cooler of appropriate size. I decided on a 10-gallon round Igloo beverage cooler that I purchased at Lowe’s for $49.99 in Grand Forks, ND. If you’re Canadian like me you’ll find that these are significantly less expensive South of the border. You can definitely use the smaller versions too for partial mashes, but I am slowly upgrading toward all-grain batches so the ability to hold 5 gallons of water plus grains dictated that 10 gallons was the right size. You can also find other brands like Rubbermaid of similar quality for similar prices.

2. Hit up your local hardware store(s) for some fittings:

Hardware needed, in assembly order

Parts list, from left to right (leftmost parts are installed inside the cooler, moving toward the outside):

• (a) 2 – 3/8″ stainless steel hose clamps
• (b) 1 – brass square head plug (Watts A737)
• (c) 1 – stainless steel braided faucet connection hose
• (d) 2 – 3/8″ barb x 3/8″ MIP hose barb adapters (Watts A294)
• (e) 1 – 1/2″ FIP x 3/8″ FIP pipe reducing coupling (Watts A815)
• (f) 2 – 1/2″ faucet lock nuts (Moen M3875)
• (g) 2 – 11/16″ inner diameter O-rings (Moen M3959)
• (h) 1 – 1/2″ MIP brass pipe nipple (Watts A836)
• (i) 1 – thick as possible O-ring with at least 1/2″ inner diameter (not pictured)
• (j) 2 – 1/2″ galvanized washers
• (j) 1 – 1/2″ x 1/2″ brass ball valve
• (l) 1 – 1/2″ MIP x 3/8″ FIP brass pipe hex bushing (Watts A828)
• 1 roll teflon tape

3. Remove the existing spigot from your cooler. This is easily done by unscrewing the interior plastic nut.

4. Wrap any visible threads with teflon tape to create a water-tight seal.

5. Assemble the ball valve. Insert one of the hose barb adapters (d) into the pipe hex bushing (l). Insert the male end of the pipe hex bushing into the ball valve (j) as shown. (Yes, I now realize the ball valve is backwards in the picture…)

The ball valve fitting that will form the spigot to our mash tun

6. Insert the brass nipple (h) into the spigot hole. Inside the cooler, stretch one of the O-rings (g) over the nipple and follow with a lock nut (f) to create a seal on the inside.

Inside view of the bulkhead

7. Attach the coupling (e) to the remaining thread, then screw the other barb adapter (d) into the coupling.

The hose barb attached to the bulkhead

8. On the outside of the cooler, stretch the larger O-ring (i) over the nipple and push against the cooler wall. Add two washers (j), then add the last small O-ring (g) and optionally the second locking nut (f) if you enough thread bare. This should now be nice and tight when all screwed together.

Outside view of the cooler bulkhead

9. Attach ball valve assembly from step 5 to the nipple.

Ball valve attached to cooler bulkhead

10. At this point, stop and fill with water to make sure your fittings are watertight. If you detect any leaks, check your connections, particularly where the o-rings press against the cooler. If it is indeed watertight, congrats! You’re almost done.

11. Now you need a way to strain your wort. To build the filter, cut both ends off the braided faucet line (c) with a hacksaw or a dremel.

The end of the faucet line after being sawed off with a hacksaw

12. You’ll have to remove the tube lining the stainless braid. To do this, carefully push the braid off the tubing with needlenose pliers to expose it. Grip the tubing and pull slowly and firmly while pulling on the braided casing in the opposite direction. Be extra careful to pull in the opposite direction of the braiding – you don’t want that to unravel accidentally.

Tubing being pulled from stainless braid

13. Once the tubing is removed, you’ll have a flimsy feeling stainless steel braided hose. This forms the filter for your wort, since the grain particles are too large to get through the gaps in the braid, but liquid can easily flow through it. The edges of your braid will be frayed on both sides, so use pliers to bend those inward to guard against nasty cuts and scratches to your cooler. Insert the square head plug (b) into one end of the braid.

The end of the stainless steel wort filter

14. Tighten one of the hose clamps (a) around the end of the filter to make sure it doesn’t separate from the head plug.

End of wort filter with hose clamp

15. Slide the other end of the filter on to the hose barb inside the cooler and fasten with another hose clamp (a).

Wort filter attached to hose barb

16. Huzzah! It looks like the inside of your cooler is done now too. Fill with water and test it out to make sure it’s not leaking again.

The converted cooler mash tun, all ready and ready to mash

17. There’s nothing left to do but put it to use. Sterilize the inside and spigot, rinse it out, and get mashing!

My first test mash in the new mash tun

So there you have it! You can now go off and build your very own mash tun to expand your setup or make life easier on yourself – and you can do it for under $100. Like I mentioned earlier, I experienced great results on my first mash with this setup.

I should also mention that this also gives you the option of adding a false bottom if you choose to go that route. I plan to in the near future, but the stainless braid was a nice cheap alternative that got me mashing before I decide exactly how the false bottom should work. Of course, I will be updating this blog with any upgrades I do to my setup so stay tuned!

If you do have any questions about any of this or ideas on how to improve on this, please don’t hesitate to leave a comment or find me on twitter at @impossibrewbeer