How to Make a Mash Tun for Brewing All-grain Beer

A mash tun is a vessel used in brewing all-grain beer, that can hold and maintain grain and water at a specified temperature, for a given amount of time. There are many types of mash tuns out there, but we are building a passive mash tun. In other words, there will be nothing actively heating the contents of the cooler. Water will be heated prior to filling this mash tun, and the mash tun will maintain that temperature.

Here's how I did it.

Step 1: Things You'll Need

Here are the things we'll need. I personally use stainless components for my brewing equipment because is much easier to maintain. You can use other materials, but make sure everything you use is food grade and keep things clean.

1 - 10-gallon Igloo cooler http://goo.gl/lklk4u

1 - 12 inch false bottom http://goo.gl/5Yx8n2

1 - 1/2 inch ID silicone high temp tubing, approximately 3 feet http://goo.gl/y4Suyi

1 - Teflon seal tape http://goo.gl/WEG9xE

1 - 1/2 inch three-piece stainless valve http://goo.gl/3HVV6I

3 - 1/2 inch large ID stainless washer http://goo.gl/8HrN9E

1 - 1/2 inch NPT nipple http://goo.gl/irVNnZ

1 - 1/2 inch NPT o-ring http://goo.gl/aKcZDs

1 - 1/2 inch NPS locknut http://goo.gl/KpduMn

1 - 1/2 inch female NPT hose barb http://goo.gl/rqbUcR

1 - 1/2 inch stainless F-style camlock fitting http://goo.gl/fQyT27

2 - Channel lock pliers or equivalent http://goo.gl/SoAzuq

Step 2: Prepare the Cooler

So we have a nice, insulated vessel that can maintain temperatures quite well. The only problem is that we don't have a way to connect hoses or a false bottom to this vessel. The outlet of the drink valve is so small that it would take forever to drain the mash. Also, that push button might get a little annoying if you have to hold it the whole time. None of these are concerns of ours though. We're going to install a ball valve. Before we can install that valve, we have to remove the drink valve. This is how you do it.

Unscrew the retaining nut from the back of the drink valve.
Remove the gaskets and the retaining nut.
Remove the drink valve.

Step 3: Assemble the False Bottom

The false bottom is used to keep solids like grain husks from getting into the wort. Wrapping the edge of the false bottom with silicone tubing will prevent solids from bypassing the false bottom. This is how I do it.

Cut a length of silicone tubing equal to the circumference of your false bottom.
Carefully, slice one side of the tubing lengthwise.
Slide the open edge of the silicone tubing onto the edge of the false bottom, starting inline with the nipple.
Work the tubing around until the two ends meet.
The false bottom is ready to be installed.

Step 4: Assemble the Valve

Time to assemble the valve. I use stainless steel for all of my brewing equipment. It makes things much easier on the maintenance side. Three-piece valves are nice in that way too. They can be disassembled and cleaned without much effort. This is how I put everything together.

Wrap Teflon seal tape around the threads of the fittings in the opposite direction you would turn them to install them. Otherwise, the Teflon will be pushed off the threads as the fitting turns.
Open the valve (turn the valve until the handle is inline with the valve body).
The end that the handle points to is the outlet of the valve. The other end is the inlet.
Turn the wrapped threads of the pipe nipple into the inlet of the valve body.
Turn the wrapped threads of the Camlock (or outlet fitting of your choice) into the outlet of the valve body.
Using two pairs of Channel Locks (or similar) pliers, tighten the fittings slightly. Remember, you will need to take this assembly apart from time to time to clean it, and you're only trying to make it water tight.
Your valve assembly is ready to be installed.

Step 5: Install the Valve Assembly

The cooler and the valve assembly are both prepared to be installed. This is where we need to be careful and make sure everything is water-tight. You don't want to be in the middle of mashing in (brewing term) and discover leaks. Now is the time to find and fix them.

Place three washers onto the valve assembly. The Igloo cooler requires three to insure that the valve can close completely without the handle running into the cooler. If you use a different brand, you will need to adjust yours to fit.
Fit the valve assembly into the opening on the cooler.
Install the o-ring and the lock nut onto the valve assembly.
Tighten the lock nut with pliers.
The mash tun may be leak tested at this point by closing the valve and filling the vessel full of water. Do this outside with a water hose as there may be leaks to fix.
If there are any leaks, tighten each joint until all leaks arefixed.
Your valve is installed and your mash tun is water-tight.

Step 6: Install the False Bottom

Now that the vessel is water-tight, we need the false bottom in place to filter out solids from the liquid wort. This is how we install the false bottom.

Fit the length of silicone tubing onto the tubing nipple on the valve assembly.
Lower the false bottom into the cooler, being careful to keep the silicone tubing wrapped around the false bottom. It will take a little wiggling to get the false bottom into place and under the valve assembly.
Align the gap in the two ends under the valve assembly, and make sure the false bottom is fully seated.
Connect the silicone tubing from the valve assembly to the nipple on the false bottom.
Your false bottom is installed.

Step 7: You Have a Mash Tun. Go Brew Some Beer!

Your mash tun is complete! You will need to remove the false bottom and tubing from the mash tun for cleaning after every use. The valve assembly does not have to be taken apart and cleaned as often as long as it is cleaned and rinsed in place.

Now go brew some all-grain beer and tell me if you like this thing.

Step 8: Extra Credit. Camlock Fittings

You can use any pipe fitting you want on the outlet side of the valve, but I use Camlock fittings for my brew system. Camlocks are simple, affordable, and reliable. This is how they work.