Converting A Cooler To A Mash-tun

Since I’ve started all-grain brewing, and because my first batch came out less than good, I’ve started acquiring more advanced brewing equipment. I got the converted keg as brew pot and have already used it on this beer, and since then I’ve converted a Coleman cooler into a mash-tun (MT). I had seen pictures of converted cooler MTs, and it seemed like a pretty simple DIY project after reading several people explain the process. So I got a 48 qt. cooler and some plumbing parts and built myself a MT this past Saturday morning. And now I’m going to tell you how I did it.

(Don’t think that just because there are like a million blogs and websites that explain how to do this that I’m going to pass up the chance to tell you how I did it. And I will try to be clearer and more detailed in places than other how-to’s I read were.)

Also, I’ve opened up a BrewDog Punk IPA (which I got in Atlanta), and I’ll give it a short review at the end of the post–kind of a Drinking It All subplot.

So first, I’ll cover what a MT is and does just in case you don’t really know. Basically a MT is a vessel (could be a cooler, bucket, or pot) that you steep grain in to get the wort you’ll boil as the second part of the brewing process. If you are familiar with extract brewing, the MT is what you’ll use to make your own extract (although, technically, it’s like extract but diluted so that it’s about 6-7 gallons vs. the 7-9 lbs of extract/syrup). The cooler (in my case) is fitted with a spigot so the wort can be drained into the brewpot and has some kind of false bottom or screen on the inside to keep the grains from coming out with the wort (I’m using a screen sock type thing, sometimes called a bazooka screen (no idea)).

Here’s what I used:

(1) 48 qt. Coleman cooler w/ spigot (mine’s blue)

(2) 1/2″ brass ball valve

(3) 3/4″ flat washers X 4

(4) 3/4″ rubber washers X 2

(5) #15 o-ring (it’s got a 3/4″ inner diameter)

(6) rubber seal from factory spigot

(7) 2.5″ brass pipe nipple

(8) 1/2″ barb w/ female thread

(9) 4′ stainless steel water supply hose

(10) 1/2″ x 3/8″ brass pipe bushing w/ male thread

(11) 3/8″ barb w/ female thread

And here’s a couple pictures with the plumbing fixtures:

(l-r) (not pictured: 1/2" barb) flat washer, factory spigot seal, 2.5" pipe nipple, (on top) factory spigot, #15 o-ring, another flat washer, rubber washer

2 flat washers, brass ball valve, bushing, 3/8" barb

Here’s what I did:

1. Removed the factory spigot from the cooler. At first, I couldn’t figure out how to do this, but then I looked at this video and felt like an idiot. You just hold onto the little circular collar that surrounds the spigot on the outside (it’s attached to the cap) and unscrew the piece on the inside of the cooler.

2.  Next, I put together half of the new spigot, in this order: (a) rolled the #15 o-ring onto the pipe nipple (from the right) (b) screwed on a flat washer, then both rubber washers, then 2 more flat washers (c) wrapped the exposed thread of the pipe nipple with teflon tape (d) screwed on the ball valve (e) wrapped the bushing with teflon tape and attached the 3/8″ barb.

It should look like this (minus the ball valve, bushing, and barb):

pipe nipple with o-ring, flat washer, 2 rubber washers, 2 flat washers, teflon tape

3. I put this part through the hole in the cooler where I removed the spigot.

4. I pushed the factory spigot seal onto the pipe nipple inside the cooler.

5. I pushed a flat washer on behind the factory seal.

6. Then I screwed on the 1/2″ barb (no teflon tape this time because it doesn’t matter to me if this leaks–it’s inside the cooler).

7. Finally I attached the screen sock/bazooka screen* to the barb with a 1/2″ metal hose clamp.

*Here’s how I made the screen sock/bazooka screen: (a) cut one end off the water supply hose with a hacksaw (b) scrunched the steel screen up away from the cut (the screen covers a rubber hose and if you try to pull the hose out, the screen will tighten on the hose like a Chinese finger trap so you have to scrunch the screen up and the hose will come right out.) (c) cut off a length of the screen about 7 inches long (d) crimped one open end of the screen.

It looked like this:

homemade bazooka screen. the left end is crimped, and the right end is attached to the 1/2" barb

And that’s all there is to it. I put some water in to check from leaks, and there were none, so hopefully, when I make the next beer later this week my MT will make the mashing process much easier than my mash-in-a-bag method from the London Pride clone.

Also, like I mentioned earlier, I’ve been drinking a BrewDog Punk IPA while writing this post so here’s the most concise (although maybe not the most detailed) review of a beer I’ve done yet.

Colored like a pale ale (e.g., Liberty Ale, Sierra Nevada PA). Bitter like a pale ale but not floral or citrusy. 6% ABV like a pale ale. Not sure what makes this an IPA. I’m giving it a thumbs down, if for no other reason than the label calls this beer a ‘postmodern classic pale ale.’ I’m not even going to try to unpack what that label might mean, especially for a just better than OK pale ale.

Oh, and here’s a picture of the MT all finished up:

finished mash-tun


2 responses to “Converting A Cooler To A Mash-tun

  1. i was looking into this cooler for making into a mash tun. i was going to purchase a 1/2″ weldless bulkhead with a stainless steel valve from amazon, and use a bazooka screen for draining. do you think these will work in the coleman 48 quart?

  2. Wow! I have the exact same cooler and was wondering if I could use it. Will try that this week-end. Thanks for you post! The level of details will help me a lot.


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