Author’s Note: Post contains affiliate links.
Welcome to the 5th step in our process of building an all-grain brewing system. This tutorial will show you how to build a mash tun from a standard rectangular cooler. Commercially available cooler-style mash tuns cost around $130 + shipping. This DIY project uses around $35 in parts + a $20-$35 cooler (depending on size). Overall, this will save around 50-60% off purchasing a pre-built mash tun!
Coolers work very well as mash tuns, because they have insulation to keep temperatures stable during the whole mash process. The drawback I’ve discovered is it can be difficult to raise a mash temperature if you miss initially. This process is a relatively simple build. For mine, I used an old 50-qt cooler I already had. You will need the following items:
- 48-Quart Cooler for 5-gallon batches
- 70-Quart Cooler for 10-gallon batches or high gravity 5-gallon batches
Shopping List (use links below or print this list and take it to the plumbing department at Lowes/HD – the associates should be a big help)
- 3/8-inch OD Copper Tubing
- Hose Clamps
- 3/8-inch Compression x 1/2 Female Fitting
- 1/2 x 1-1/2-inch Pipe Nipple – Can be hard to find in stores
- 1/2-inch Ball Valve
- 1/2-inch NPT x 3/8-inch Barb
- 1/2-inch Stainless Steel Braid – Least expensive I could find for 5-ft length
- Teflon Tape (Plumbers Tape)
- Tubing Kit – Optional for cutting and bending copper tubing without kinks
- Small Nail
Step 1 – Install the Valve
Locate the drain on the cooler and remove the plug assembly. This should simply screw apart, and you will no longer need these parts. Add teflon tape to the pipe nipple and thread it through the hole in the cooler. Screw the ball valve onto the threads outside the cooler, and screw the barb fitting into the ball valve. On the inside of the cooler, screw the compression fitting onto the threads. Tighten the inside fitting and outside ball valve until they are flush against the walls of the cooler. Do not over-tighten, or the plastic could crack.
Step 2: Build the Manifold
The advantage of using a manifold over a simple bazooka screen is that it forces the wort to drain from the whole mash tun, instead of a single point at one end. This can help with efficiency and eliminate “dead zones” in your grain bed. John Palmer did an experiment using food coloring and an aquarium to illustrate dead zones. It’s very important to rinse the entire grain bed, otherwise you are wasting grain that you paid for, resulting in poor efficiency and ::shudder:: wasted money! Another experiment by Mr. Palmer notes that the manifold should be configured in a way that provides the shortest path for the wort to get to the drain. I have not found this to make a difference in my efficiency with my patented (not) spiral manifold design.
Cut a section from the copper tubing with a length between 3- and 5-feet. I used my angle grinder for this cut, but you can use a tubing cutter (linked above). Uncoil the tubing and carefully shape it to fill the bottom of the cooler as thoroughly as possible. More coverage = less dead zone. Once you have your tubing shaped, bend the end slightly upward to fit into the compression fitting. Do not secure it to the fitting yet.
Once the manifold has been completely shaped, remove it from the cooler. Turn it upside down and use the hammer/nail to punch small holes into the bottom approximately 1 inch apart. Cover the entire length of tubing with these holes. It is important that these holes are on the bottom of the manifold to allow it to pull wort from the lowest level of the mash tun. Otherwise, you could leave behind any wort sitting below the holes. After punching the holes, use a pair of pliers to squeeze the end of the tubing closed tightly.
Now you will need to remove the stainless steel braid from its hose. Cut the ends off of the hose (I used the angle grinder again), and slowly remove the stainless steel braid from around the hose. This process is a bit like removing a Chinese finger trap from your fingers. Once you remove the braid, slide it over the length of the copper tubing manifold. Secure it on the open end with a hose clamp, and DO NOT over-tighten. Also, be sure to leave room for the compression fitting attachment. Use pliers to secure the other end – fold the braid and copper over and squeeze to create a seal. Now that your manifold is complete, place it back in the cooler and attach it to the compression fitting. Tighten securely to prevent air from entering the seal. Some people use small o-rings to ensure an air-tight seal. Manifold complete!
**Many brewers report success with only a SS braid. However, I recommend the use of the copper manifold + SS braid for a couple reasons:
- See the linked experiment by John Palmer. A manifold will cause the wort to drain from all parts of the mash tun, not a single point at the drain. Based on the way the cooler drains, I prefer to be pulling wort from the entire grain bed through the manifold to prevent dead zones.
- Adding the braid to the manifold prevents a stuck sparge from grist clogging the manifold holes.
Step 3 – Build the Sparge Arm
Adding a sparge arm will allow you to rinse the grains while the lid is closed. This helps maintain a stable temperature through the entire process, particularly in cold weather. With this setup, you will also be able to fly sparge (my preferred method).
Select a drill bit with the same diameter as the copper tubing and drill a hole directly through the center of the cooler lid. Cut another length of copper tubing the same length or slightly longer than the first, and shape it in a similar fashion. However, this time you will need to bend the end section in the middle upward. This will go through the hole you just drilled in the cooler lid. Use the hammer and nail to punch holes into the tubing, and clamp the end closed. Slide the section of tubing up through the hole in the cooler lid and secure it on the outside with a hose clamp. Approximately 1-inch of tubing should protrude through the lid. Make sure the whole piece is mounted as tightly against the cooler lid as possible. When you run the sparge water into the top of the tubing, it will sprinkle water evenly over the grain bed, even with the cooler lid closed!
There you have it! Now you can convert those milled grains to sweet sweet wort in your brand new mash tun. A few tips for cooler mash tuns:
- Preheat the cooler – Before adding your grain, run some heated strike water through the sparge arm and into the cooler, with the lid closed. Wait a couple minutes for the water to warm the inside of the cooler, and then dump it out. This will lower your risk of missing your mash temperature on the low end.
- Keep the lid closed – Once you hit your mash temperature, resist the urge to open the lid and peek in for any reason. The cooler is very good at maintaining temperatures, but heat escapes quickly when you open the lid. Wait the full mash time before opening.
- Use a thermometer with a corded probe – This is the thermometer that I use. It will allow you to monitor mash temperature with the cooler lid closed. It also has a timer and temperature alerts, which are very useful during all parts of the brewing process.
- Add more hot water to raise temps – This is definitely not ideal, but you may miss low on your target mash temp. If so, add more water from the Hot Liquor Tun while stirring. Do this until your desired temperature is reached. Move the temperature probe to ensure no “hot pockets.”
Enjoy your new mash tun, and keep following along as we continue to build a complete all-grain brewing system. Cheers!