Instructional: How to Make a Mash Tun

In my previous post, I put up a video and promised to post more details. Here is a step-by-step guide that accompanies the video I made. There is much more space here, so if the video left you with a few unanswered questions, hopefully you'll find what you need by reading this.

Overview
I needed to make a new mash tun because my current one, a 5 gallon drink cooler, was too small. It only held about 12 pounds of grain, and prevented me from making big beers and 10 gallon batches. The solution was to build a much larger mash tun. You'll see how I designed the mash tun, starting with...

The Cooler
I selected a 52 quart Coleman cooler from Kmart. It cost $35, has plenty of room for grain, and also accommodates the manifold design.

Front view

Side view, the drain valve will be removed

Note the valley by the drain valve

Manifold Design Considerations
I currently do fly sparging, so there were a couple design considerations to support this. The first was even slit distribution so that drainage is even, and the second is proper spacing of the manifold across the bottom and away from the edges. However, I will want to do batch and no-sparge in the future, so the number of slits needed to be high enough to allow for fast drainage.

Exploded view of manifold and valve

From left to right:

• 1/2" threaded brass ball valve ($7.32)
• Brass washer ($1.09)
• Rubber o-ring (about $2 for a pack of 10)
• 1/2" x 2" brass nipple ($4.56)
• Rubber o-ring
• Brass washer
• 1/2" copper female adapter ($4.17)
• 1/2" type L copper piping (3 24" lengths, $7.44 per unit)
• 1/2" copper tees (8 at $0.97)
• 1/2" copper caps (5 at $0.68)
• Not shown: 1/2" copper street 90 (2 which I had already)

Exploded view of valve assembly

Valve assembled, cooler wall will occupy space between o-rings

Dry Fitting
Once the measuring was done (took advice from John Palmer's How To Brew online resource, appendix D) and the plan was put on paper, the pipe needed to be cut. You can use a reciprocating saw with a 18 tpi metal blade, a hack saw, a multi-tool, or a pipe cutter. I have the latter, and it simply involves rotating it around the pipe and gradually screwing in the cutting wheel.

A pipe cutter makes nice even cuts

Here is the dry fit

Soldering
Some people fit the pipe and fittings together with friction, but I prefer soldering because it makes it nice and solid so it won't come apart when I stir the mash. The image below shows what is needed.

Torch, solder, q-tips for applying flux, the flux, and sandpaper

First, sand the ends of the copper piping. This exposes bare copper, which will more easily accept the solder.

Do the same with the inside of the fittings where the copper pipe will be joined.

Apply flux to the outside of the pipe where you just sanded. The flux is an acid-based paste that cleans the pipe when it gets heated, so that the pipe will better accept the solder. Since it is acidic, I use a q-tip to apply it.

Repeat the process for the inside of the fittings to be soldered.

When you're done applying flux and assembling, it should look like this, ready for soldering. I put scrap piping under the manifold to lift it off the wood so that it can be heated without burning the wood.

When you solder, apply heat to the fitting. You'll probably see flux dripping out of the joint, and maybe hear some crackling as it heats up. Then gently touch the solder to a joint. If the copper is hot enough, the solder will get sucked into the joint and migrate around it. If this doesn't happen, just apply a little more heat and retry.

Applying heat with propane torch

Solder just beginning to migrate into joint

Remember that this manifold won't be seeing any pressure, so the soldering doesn't need to be as perfect as it would be for a water line. The solder is just keeping it from coming apart.

Slitting the Manifold
After soldering and allowing the manifold to cool off, I was time to slit the piping. An important point to remember is that fly sparging requires even distribution of the slits, so only the long horizontal pipes need to be cut. If the short cross-pieces get cut, you'll end up was a zone where drainage will be favored, potentially making your extraction uneven.

For making the slits, you can use a variety of methods:

• Hack saw: labor intensive, difficult to get into tight areas
• Reciprocating saw: costly, fast, little difficult to control, difficult to get into tight areas
• Multi-tool: medium cost, blades are expensive
• Dremel tool: medium cost, very accurate, you'll go through a few cutting wheels

Whatever method you select, just make sure your slits are fairly evenly distributed, even through the tees.

Partially slit manifold, clamped to work bench

Fitting the Valve
Remove the drain from the cooler and install the valve assembly. Be sure to use teflon tape on the threads, and tighten well. It's a good idea to partially fill the cooler with water and let it stand for a while as you look for any leaks.

Exterior view of installed valve

Interior view, after water test

Installation
The manifold needs to be cleaned before it gets installed, because it has burrs from the slitting, and it still has flux from the soldering. I simply sanded the outside with fine sandpaper, and sanded the inside with a strip of sandpaper that I put through a flute cleaner and ran through with a drill. This got rid of a bulk of the burrs this way. For the flux, I used carburetor cleaner, which is mostly alcohol. This stripped away the flux really well, and I cleared the manifold further with hot soapy water after that.

Installed and ready for mashing

A couple points about the installation:

• I added 2 street 90s on the end to keep the manifold centered in the cooler.
• The drain assembly is lower than the manifold, so I used a piece of PVC braided hose to join them. It fits very snug, so there is no need for a clamp (but feel free to add one if you'd like).
• To allow for easy cleaning of husks and grain particles, the caps are removable. To keep them in place, simply squeeze the end of the pipe very slightly with some channel locks, and then push the cap on.
• To provide easier access, I removed the hinges from the lid while I was working. I've decided to keep the hinges off so that I can have unencumbered access during mashing.
• Since my mash tun was young, inexperienced, and plastic, I named it Mashtun Kutcher. ;^)

Mashtun Kutcher in action, fly sparging for an imperial IPA