Simply put, a mash tun (pronounced “mash ton”) is a vessel used for all grain brewing to convert the starches in crushed grain into sugars to be used for fermentation. There are many different types of mash tuns used by brewers of all skill levels, but the basic pieces of any mash tun usually includes an insulated container with a filtration device in the bottom that allows liquid to pass through while holding the crushed grains back.

In this post we will be converting a Rubbermaid 52 quart rectangle cooler into a mash tun. The process is very simple and we only use basic, necessary tools and equipment. There are no frills here. To date this is our prefered style of mash tun as it is cheap, easy to work with and very functional for the average homebrewer. One point to make note of before we move further is that we typically batch sparge when we brew. If you are planning on fly sparging you may want to consider a round 10 gallon Rubbermaid/Gott cooler. They are more expensive but due to their shape they are far more effective when fly sparging. The information in this post should appy to either type of cooler.

TOOLS:

• 2 pair channel lock pliers
• Flat head screwdriver
• Scissors
• Hacksaw
• Teflon tape

EQUIPMENT:

• 1 – 52 quart Rubbermaid Rectangle Cooler: These are usually easy to find, but there are a few things to keep in mind before making your purchase. We used a 52 quart cooler because that is what we had. You can use any similar size that you may stumble upon. Ensure that the bottom is flat! A small dip in the bottom leading to the drain is ok, but stay away from anything that might have drink holders, wheel wells, etc.
• 1 – 20″ Stainless Steel Braided Hose: These are easy to find in the bathroom/laundry supply section of any hardware store, but beware; they make many of these out of plastic. They look almost exactly the same so be sure that it says “Stainless Steel”.
• 1 – 3′ to 4′ Food Grade Quality Plastic Hose: We usually use ~ 3′.
  
• 1 – 1/2″ Threaded Brass Ball Valve
• 3 – 1/4″ to 5-8″ Hose Clamps
• 2 – #15, 1/8″ Thick Rubber O-Rings
• 2 – Watts A-385 1/2″ MIP to 1/2″ Hose Barb
• 1 – Watts A-836 1/2″ x 1-1/2″ MIP Brass Pipe Nipple
• 1 – Watts A-390 1/2″ FIP Brass Barbed Hose Adapter
• 1 – Watts A-819 1/2″ Brass Pipe Cap

Step 1:

We will begin with the stainless steel braided hose. Place one end of the hose on a steady surface or in a table top vice. We use the vice because we have one available, but it is by no means necessary. Cut off each tip with the hacksaw. We like to use a pair of scissors to finish the cut just to help keep the steel braids from fraying.

Step 2:

Grab the hose firmly with one hand. Use your other hand to pull back on the steel braid close to where you made one of your cuts. The steel braid should pull back to reveal an inner lining of plastic tube. As soon as you expose enough of this tube to grab onto, pull it out and discard it. Be careful with the steel braid from this point on; it can bend and twist very easily.

Step 3:

Place two of the 1/4″ to 5-8″ hose clamps onto your braided steel hose. Insert one of the Watts A-385 1/2″ MIP to 1/2″ Hose Barbs into one end of the hose and the Watts A-390 1/2″ FIP Brass Barbed Hose Adapter into the other. Clamp the hose onto the nipple end of the Watts A-385 1/2″ MIP to 1/2″ Hose Barb and Watts A-390 1/2″ FIP Brass Barbed Hose Adapter. Place the Watts A-819 1/2″ Brass Pipe Cap onto the end with the Watts A-385 1/2″ MIP to 1/2″ Hose Barb and set this assembly asside.

Step 4:

Remove the spigot from the cooler. Our cooler has a plastic hex nut that was easily removed; yours may differ slightly. Pull out the spigot once the necessary nuts, washers, etc. holding it on have been removed. Save any pieces once removed, you may need them later.

Step 5:

Prepare to assemble the new mash tun valve/braided hose filter contraption.

NOTE: This is where things can get tricky. We have two mash tuns of this variety assembled out of different types of coolers. For each build we had to modify the way the valve/braided hose assembly attached to the cooler. On this build we had to use the plastic hex nut, plastic washer and rubber gasket that we originally took off of the cooler in order to get a nice snug fit for the entire assembly. Our other mash tun fit together in a slightly different way; we only had to use the plastic washer to get a snug fit. The main point of this note, should you have to strike out on your own and reconfigure this set-up is; the valve/braided hose assembly MUST fit through the cooler and be held in as tight as possible with gaskets pressed firmly against the inner and outer walls of the cooler. Your beer depends on it!

Step 6:

Fit the Watts A-836 1/2″ x 1-1/2″ MIP Brass Pipe Nipple through the open hole in the cooler and place gaskets on each end. We used the gasket that came off of the cooler on the inside and 2 of the #15, 1/8″ Thick Rubber O-Rings on the outside.

Step 7:

If applicable slide the plastic washer onto the Watts A-836 1/2″ x 1-1/2″ MIP Brass Pipe Nipple on the inside of the cooler. Now attach the braided hose assembly to the Watts A-836 1/2″ x 1-1/2″ MIP Brass Pipe Nipple.

Step 8:

If applicable on the outside of the cooler slide the plastic hex nut that came off of the cooler previously onto the Watts A-836 1/2″ x 1-1/2″ MIP Brass Pipe Nipple and firmly tighten; re-exposing as much of the thread of the Watts A-836 1/2″ x 1-1/2″ MIP Brass Pipe Nipple as possible. At this point the Watts A-836 1/2″ x 1-1/2″ MIP Brass Pipe Nipple should be sealed nice and snug within the cooler wall.

Step 9:

Wrap some teflon tape onto the exposed thread of the Watts A-836 1/2″ x 1-1/2″ MIP Brass Pipe Nipple and attach the 1/2″ Threaded Brass Ball Valve. Ensure that when the 1/2″ Threaded Brass Ball Valve is open the handle faces away from the cooler.

Step 10:

Wrap some teflon tape onto the thread of the remaining Watts A-385 1/2″ MIP to 1/2″ Hose Barb and attach it to the 1/2″ Threaded Brass Ball Valve. Place a length of Food Grade Quality Plastic Hose onto the nipple of the Watts A-385 1/2″ MIP to 1/2″ Hose Barb and secure it with a 1/4″ to 5-8″ Hose Clamp. We usually use about 3 feet of tubing when we brew because it suits our set-up, your prefered length may vary.

Congratulations! You are now the proud owner of your very own mash tun. Slap some brewery stickers on that puppy and make some beer!!!

Be sure to replace the hose occasionally and clean thoroughly before use.

Try to be carefull when stirring your grist so that you do not scratch the sides of the cooler. A wooden mash paddle comes in very handy.

If after reading this you’ve decided that you’d rather just save your time and spend some extra money; Adventures in Homebrewing has a large selection of prefabricated mash tuns to fit any homebrewers needs. Just do a search for “mash tun” when you get to their site.

Please give us feed back of any sort in the comments section. We are always looking to make things better!