Building a 5 Gallon Mash Tun

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Do you have an Igloo brand cooler that was only used a couple of times? Are you a homebrewer? Do you like to make great beer? Want to make your own mash tun inexpensively? Look no further and read on!
A mash tun is a container that can hold temperature and extract all the fermentable sugars from crushed grains. If you steep your grains or use a BIAB system you essentially are mashing to extract the sugars from the grains. This requires that you hold a temperature with the grains suspended in the water for a period of time (60-90 minutes). If you like to sit and watch a pot with a thermometer in it for an hour or longer just stop reading right now. If you have continued to this next sentence then sit back, relax and have a home brew and read on!
Instead of constantly heating your mash water, you can turn your average insulated cooler into a mash tun that very effectively holds a tight temperature range without needing to constantly apply heat that will melt your cooler BTW! If you use an insulated cooler, it will hold and retain the heat of the water placed inside for your mash time.
What You Need
  1. Insulated cooler (Igloo, Rubbermaid, etc) that will be large enough to hold your grains and water. I chose a 5 gallon cooler since that is what I had.
  2. 1 " 1/2 in x 1 1/2 in brass nipple (Watts LFA-836)
  3. 3 " 3/8 in ID x 3/8 in MIP brass hose barb (Watts LFA-294)
  4. 3 " 1/2 in MIP x 3/8 in FIP brass bushing (Watts LFA-828)
  5. 1 " 1/2 in MIP Brass tee (Watts LFA-808)
  6. 1 " 1/2 in threaded brass ball valve, Full port
  7. 1 " 3/8 in x 3/8 in x 48 in Braided Polymer Dishwasher Connector hose
  8. 2 " in rubber washers thick enough to seal the hole
  9. 2 " 3/8 in stainless steel hose clamps
  10. 2 " in locking washers (found where the electrical section of your store is)
  11. 1 " Roll of Teflon tape
  12. 2 " 10 or larger adjustable wrenches
  13. 1 " Plyers
  14. 1 " Needle nose plyers
  15. 1 " straight tin snips (or anything to cut the ends off the dishwasher hose)
1. The first thing you want to do is to remove the valve completely from the cooler. This may require the plyers and/or adjustable wrench depending on how it is installed into the cooler.

2. Use the brass nipple and one of the locking nuts and washer and install the nut and washer close to the middle of the nipple.

3. Apply Teflon tape to the end where the washer and nut are.
4. Screw the in tee into the nipple over the Teflon tape, make sure it is tight and snug.

5. Next put some Teflon tape on the threads on the hose barb connector and screw together the bushing and the hose barb connector.

6. Now place Teflon tape on the exposed threads of the hose barbs and screw two of them into the other ends of the tee.

7. Use the metal sheers cut the ends off the braided hose and discard them in the trash.

8. Carefully with the plyers grab the interior hose and push back the stainless steel braiding and remove the hose.


9. What you are left with is a hose (to be used later) and the stainless steel braid. We will be using the braid as the filter for the grains instead of a false bottom.

10. Push one end onto the hose barb along with a stainless steel hose clamp.


11. This is with the one side connected. There is no need to use the Teflon tape.
12. Measure and cut the mesh braid at any time.
13. Install the tee connector through the cooler wall and secure it on the other side with another rubber and lock washers to the cooler. G the teflon tape install the remaining hose barb in the the out port on the valve.

14. Using the hose barb and reducer install them on together
15. Thread another washer and lock nut onto the end of the nipple inside the cooler.

16. Insert the inner tubing from the braided hose over the barb on the outside.
When I was finished I heated about 4 gallons water up to around 165 degrees and filled the mash tun and made sure there were no leaks and also to time and see the temperature drop, if any, for 1 hour. I checked the temp before I started the timer and after I closed the cooler. When the hour was up I removed the lid and found that my temperature was within 1-2 degrees from where I started.


Well there you have it all completed, your new mash tun. For less than $100 you can purchase all the parts needed to build your own mash tun. With this project it is also very easy to use a false bottom over the mesh tubing.
Thanks for the pictorial Joe. Looks like a fine Mash-tun.
I think you have a somewhat warped view of what BIAB involves however.
Also steeping grains and mashing in a bag are not equivalent processes.
@AQUILAS You can get into the low 1.06 OG range with 5 gallon batches. I actually did a 5 gallon Imperial with a 5 gallon cooler, but I added 3Lb of light dry extract to the boil. It came out great; the OG just did not come 100% from the mash tun.
I do BIAB in my cooler/mash tun with no modifications. I like the BIAB method because it reduces the clean up tremendously with little efficiency degradation. I plan to make a similar modification (holding the orginal cooler valve open is a pain) except I'll be leaving off the tee and the steel braid. The bag (a paint strainer big enough to fit on the cooler) is providing sufficient macro-filtering for now.
@Kennanwt5 He just says that you have to clean brass with vinegar and hydrogen peroxide to avoid surface lead contamination, brass fittings on a mash tun are extremely common.
The Cheap'n'Easy system is...well, cheaper and easier. And works every bit as well.
I'd highly advise anyone who reads this article to NOT use brass but instead opt for all stainless fittings. This build also seems like overkill. All you need is a SS nipple, coupler, barb, washer, a silicon washer, and ball valve. False bottoms for these are like $30, well worth it rather than jimmyrigging it with that braided hose.
I have a similar rig. I have a CPVC valve.
On the inside I have a cutting board cut to the size of the bottom to reduce lost volume. I have CPVC tubing on the inside drilled with lots off holes to help with the flow to the valve, instead of your braid tube.
I use a regular 5 gallon paint straining bag for the grains. It acts as a filter, and is a great fit for the cooler.
Including the bag, valve, rubber seal material, tubing and connections, I'm guessing my cost to modify the cooler was less that $15. Probably closer to $10.
I've probably used it for 50 batches, with about 8 lbs of grain each time. I partial mash on my stove, so I am limited by my boil volume. If I did a full boil, I could easily mash 10 lbs of grain (1.060 in 5 gallons), and possibly up to 12 lbs of grain (1.070 in 5 gallons).
Consider carefully whether a 5 gal MLT is right for you. I make 7 gal batches and push the limits of my 10 gal MLT. You don't even have to do the math to know that a 5 gal MLT would be undersized for 5 gal batches, for me anyway. I know people make it work, but why not go a little bigger and save the hassles?
Yes I built one for cheaper than $100 using a 12 gallon Igloo Cube cooler and a copper tube manifold that I cut slits in ever 1/8 to 1/4 inch using a hacksaw. It worked great and I sure could get a lot of grain in it. I used it a lot for 5-6 gallon all-grain batches.
One problem with those braided bazooka-type hoses is that they are easy to crimp when you're stirring your mash. Ask me how I know. I still use one but I wrap some stainless mesh around it so my spoon can't touch the hose.
@beernutz I have used the same SS braid for 485 batches and it still works fine. If you get the right braid and don't make it too long, you should have no problems.
Actually one can use a regular square type cooler which holds considerably more mash which enables you to use more grain, and get more brew water, volume and gravity!
I did the exact Same thing with a 10gallon, and a bazooka filter.
@Kennanwt5 Nothing wrong with most brass available these days as it is lead free and will say so on the packaging. Not so sure about that zinc clamp though!
To not worry about a stuck mash you may get 1/16 th inch welding wire of stainless steel and wrap it around a small diameter dowel. Stick on end into the plastic tube and as you remove the tube the coiled wire can be pushed into the braided stainless filter. this should help it from any collapsing.
most (plumbing) brass sold these days are lead free materials.

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