Homebrew DIY: How to Convert a Cooler into a 40lbs Mash Tun

This Homebrew How-To shows you how to convert a 70-quart cooler into an all grain mash tun capable of mashing just over 40lbs of grain, and all for less than $100! You can also adjust these instructions to make a similar mash tun out of smaller or larger coolers.

These easy steps will quickly turn that useless insulated box into a machine for turning grains into drunkenness.


Full disclosure: These are the lowest prices I’ve found online, but I do get a couple of pennies if you buy the parts from some of the links (Amazon) below. (bloggin’ ain’t free!)


Parts Needed:

– 1 x 72-quart Cooler (Recommend Coleman XTreme) – $39.88

– 1 x Bulkhead Fitting (Thick Wall) w/ Stainless Ball Valve – $25.00

– 8 x 1/2″ CPVC 90-degree elbows – $5.44

– 12 x 1/2″ CPVC Tee Fittings – $10.08

– 1 x  3/8″ (ID) Neoprene Washer – $1.62

– 1 x 1/2″ CPVC fitting, slip to NPT Male adapter – $0.33

– 2 x 1/2″ CPVC pipes (10ft each) – $7.10

– 1 x Large Grain Bag (optional) – $10.19

TOTAL COST: $99.64


Tools Needed:

– Drill

– 1/2″ drill bit

– 3/32″ drill bit

– 1/16″ drill bit

– PVC Cutter



Installing the Ball Valve:

1. Begin by removing the drain that comes with the cooler. There is a nut on the inside of the cooler that you should be able to remove by hand.

2. Place the bulkhead fitting through the hole where the drain used to be. Use the washers and o-rings included with the fitting, along with the neoprene washer. Use the below photos to see what order to place them in. NOTE: You may need additional washers or o-rings to make this fit properly due to differing widths of cooler walls.


3. Screw the valve onto the bulkhead fitting on the outside of the cooler. See the above photo as an example.

4. Screw the CPC Slip to NPT Male adapter into the fitting on the inside of your cooler. See the above photo as an example.

Building the Bottom Manifold:


1. Cut one CPVC pipe into the following sized pieces:

– 4 x 18 inches

– 5 x 2 inches

– 2 x 3/4 inch

– 1 x 3 inches

2. Use the 1/16″ bit to drill holes all along one side of all the 18-inch, 2-inch, and 3-inch pieces of CPVC. I recommend spacing these whole about 1/8 of an inch apart. Make sure you do not drill all the way through the pipes.

3. Take the 3-inch piece of CPVC and drill one 3/32″ hole on the side with no holes in it. This hole will allow air to escape from the mashtun manifold when you fill it with water.

4. Now gather the following parts:

– 5 x CPVC Tees

– 4 x CPVC 90-degree elbow

Manifold Part Sizes

5. Attach all parts as indicated in the photo above. When complete the manifold should have all the holes on one side just like the one in the below photo.

14 - 7

6. Place the manifold in the mash tun with the holes pointing down.

14 - 5

7. (Optional) place the manifold in the large grain bag. Install the manifold back in the mash tun. This will filter out the larger pieces of grain before they even get to the wholes in your manifold.


Building the Sparge Manifold:

1. Cut remaining CPVC pipe into the following sized pieces:

– 4 x 7.5″

– 4 x 5.25″

– 6 x 3″

2. Using the 3/32″ bit, drill holes spaced one inch apart into two (2) of the 7.5″ pipes, four (4) of the 3″ pipes, and  all four (4) 5.25″ pipes. Using the same bit, drill holes spaced 1/2″ apart into the two (2) remaining 7.5″ pipes. Make sure you do not drill all the way through any of the pipes.


3. Gather the following parts:

– 7 x CPVC Tees

– 4 x CPVC elbows

4. Assemble the sparge manifold as indicated in the below photo. All holes should be facing upward, and the 7.5″ pieces with smaller spaces between the holes should be on the ends of the manifold.

Sparge Manifold Sizes

5. Using the 1/2″ drill bit, drill a hole through the lid of your cooler.

6. Stick a short piece of remaining CPVC through the hole. This may be difficult at first as there is likely to be bits of insulation clogging the hole.

7. Open the lid to the cooler and attach the sparge manifold. It may fall off at first, but it will be much more secure when the hot mash causes it to expand slightly.

8. To sparge, simply connect a hose to the end of the CPVC pipe that is sticking out of mash tun’s lid, and let the sparge water slowly flow.


There you go. If you have any questions just ask in the comments!


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