Building your own mash tun is inexpensive and simple, even for those of us that don’t qualify as DIY experts. 

 

This project will walk you through the construction of a round mash tun using either a 5-gallon (19-L) or 10-gallon (38-L) round picnic-style cooler.

 

A round mash tun will give you the ability to experiment with both fly sparging (which is more efficient with a round-shaped tun) and batch sparging (the mash efficiency of which generally isn’t affected adversely by tun shape). 

The total cost will vary depending on the seasonal availability of coolers in your area, whether you choose brass or stainless steel for the weldless fittings, and if you opt to use a plastic false bottom or a stainless steel model. 

For a 5-gallon (19-L) tun with stainless steel parts, the cost should be about $75.

Step 1: Place the false bottom

The reason we’re putting the false bottom in first is because, depending on the exact inner circumference of your cooler, you might not be able to fit it in easily once the bulkhead and hose barb fitting are installed. 

This likely won’t be a problem, but playing it safe by putting the false bottom in first is a good idea.

First, remove the factory cooler spigot by unscrewing it from the inside of the cooler. Once that’s out, just place the false bottom in the cooler with the attached barb facing up.

 Step 2: Install the bulkhead

The cooler conversion kit is composed of two main parts: a bulkhead fitting and a ball valve. The bulkhead is further composed of parts that screw together to form a water-tight seal through which your wort will flow when lautering and sparging. 

The ball valve allows you to control the rate of flow through the bulkhead. Start by putting the bulkhead fitting (the cylindrical silver-looking part) through the spigot hole from the inside of the cooler.

Make sure the small rubber seal goes on the inside of the cooler. Next, put the large rubber seal over the threads of the bulkhead on the outside of the cooler. 

Now tighten the brass nut on the outside of the cooler, making sure that the grooved side of the nut faces in towards the large rubber seal. Tighten the nut just until you get some resistance. Hand-tighten the whole assembly from the inside of the cooler by turning the bulkhead. 

Once it’s good and tight from the inside, you can use an adjustable wrench to tighten down the nut on the outside.

Step 3: Install the hose barb

The 3/8” brass hose barb fitting screws into the bulkhead, so that the outlet barb on the false bottom (which is also 3/8”) can connect to the bulkhead via high-temp tubing.

First, you will need to give the threads on the brass barb a few wraps of teflon pipe tape. This will help to insure a water-tight seal. Next, screw the hose barb into the bulkhead. 

Step 4: Connect the bulkhead to the false bottom

We’re almost done on the inside. All we need to do now is use a short piece of high-temp 3/8” ID tube to connect the barb on the false bottom to the barb on the bulkhead. Between 2” and 3” should do it. See figure 10 for an example of the finished inside plumbing job.

Step 5: Connect the ball valve

Now, screw the ball valve into the outside threads of the bulkhead. The only tricky part here is that it can be hard to make the ball valve assembly line up with the valve handle facing up. 

If you screw the ball valve on and it does not line up correctly, use your wrench to turn the brass nut on the bulkhead until the handle lines up with the valve handle on the top.

Step 6: Test the integrity of the valve assembly

We need to make sure that the all of the fittings and connections are watertight. Even a very slow leak is a bad thing during the course of a mashing and sparging. Put at least 2.5 gallons of water in the cooler and let it sit for 30 to 45 minutes. 

If there are no leaks whatsoever, then it’s time to have a homebrew and congratulate yourself on a job well done. If you notice a leak, you need to work backwards, re-tighten each connection and test again.

Adding grain and water

Now that the mash tun has been assembled and tested, you can go ahead and get started with an all-grain recipe. Some brewers like to add all the grain to the tun and then the water, and some do the exact opposite. 

With a round tun design, I prefer to add about a third of the total grain bill to the tun and then add about a third of the water. Then I stir for a minute to break up any clumps of grain. 

Then I add the next third of grain and water and repeat the stirring, and then add the 

final third. You may find that another method works better for you, so exp-eriment and take good notes!  After all the grain and water has been added, a thorough stirring will also help even out the temperature in the tun so that cold spots or hot spots in the mash are minimized. 

Be careful when stirring not to dislodge the tubing that connects the false bottom to the ball valve. Because of the nature of the design of the false bottom, there is a small “dead spot” at the very bottom center of the mash tun. 

After the bulk of the wort has been drained into your brew kettle, you may want to lean the mash tun forward to try to recover the residual wort that’s hiding in the dead spot. It won’t amount to much, but if you are as fanatical about efficiency as I am, every drop counts. 

Monster Mashing

If you would like in-depth techniques and step-by-step guides on the process of mashing and sparging, there are a number of great resources available. You can start with “Cheap and Easy Batch Sparging” in the January–February 2004 issue of BYO!

Forrest Whitesides is the new Projects contributor for BYO.