Build a Mash Tun for All Grain Brewing

The inevitability of drinking lots of beer, and possibly also growing facial hair, is that sooner or later you’re going to want to craft your own beer.

My South African craft beer adventure is about to include brewing all grain beer, but first I need some equipment.

I’ve brewed an extract-based beer or 5 in my life, but grain brings with it an interesting set of challenges and possibilities, offering flexibility in exchange for complication. An all grain success is all that much sweeter though (or bitterer, or fuller bodied, it’s up to you).

First requirement: mash tun. Getting wort for an extract-based brew only requires working a can opener. To make your own wort from grain you need a big old teapot to steep your grains in, called a mash tun.

Yesterday I hit the shops to try and find all I needed for this project, and today I had a go at making my own mash tun for all grain brewing.

You can, of course, buy yourself a mash tun and save, if not money, then time. Yeah, you can.

What You’ll Need to Build the Mash Tun

In essence, your mash tun is a cooler box (for temperature control), into which you’ll drill a hole and install a tap, enabling the steeping of grains and draining away of the liquid, leaving spent grain behind.

All the parts required for making a DIY Mash Tun - hose connector not used

I bought everything I could from Paarl Agrimark, where everything was cheapest, plus the staff were actually interested to help me find what I needed. What they didn’t have I got from Build It.

  1. Cooler Box – R99 from Pick n Pay. The cheap, 25L Big Jim, Polypropylene (PP) cooler box was on special at Pick n Pay in Paarl Mall. After the manufacturing process Polypropylene is, apparently, innocuous and will handle mash temperatures fine without leaching any nasty chemicals into your stuff.  This Big Jim smells funny, but I haven’t aired or cleaned it properly yet. I hope the smell goes away. Another less-than-ideal trait of this cooler box is that it has rather large, concave edges on the inside where the walls become the floor. The back nuts of the tap assembly have to be flush with the cooler box wall to ensure a water-tight seal, so the cooler’s large, rounded bevel means having to mount the tap higher, and the higher up it gets the more precious wort you will potentially have to leave behind after the mash. In hindsight, I would consider a different cooler box, one with bottom edges that are not round, but flat, and will allow for a tap mount closer to the box floor.
  2. 15mm Brass Nipple – R44.14 from Paarl Agrimark – This is the core of your assembly. I guess you could get any diameter as long as everything else were sized to fit. I got one that’s 100mm in length, which is much too long and a terribly efficient heat leak. Get a shorter one.
  3. 1/2′ Back-nut Rubber Washers – R7.95 from Paarl Build It – 0.5 inch in my book is 12.7mm, but hey, it fits the 15mm brass nipple perfectly tight, so all is good. You need 2 of these, one for inside one for outside. The back nuts will tighten against them and I suppose they contribute to sealing the hole where the assembly passes through.
  4. 15mm Brass Back Nut – R15.93 from Paarl Agrimark – These tighten against the rubber washers, help with the seal and hold the assembly in place. You also need 2 of these.
  5. 15mm Hose Nipple – R7.39 from Paarl Agrimark – A tap fits on the outside end of the brass nipple. This plastic (PP) hose nipple creates a bridge between the brass nipple and the tap.
  6. 15mm Ball Valve Tap – R49.60 from Paarl Agrimark – It screws into the hose nipple above, and comes with a hose connector. I chose one without the little plastic aerator thingy in the spigot part, because you don’t want to aerate your wort at this point.
  7. Braided Connector Hose 1000mm with 15mm Fittings – R69.96 from Paarl Build It. This is the filter through which the wort will drain from the grain. The braid, hopefully, is perfect to keep the grains back and let through the wort, but inside the braid is a rubber hose, which we first need to remove. I took the longest hose they had, but I’ve since read that you only need a few inches. Not sure if it makes a difference in the end, but I’ll keep the full length in case I ever upgrade to a bigger cooler box.
  8. Drill Bit to Drill a Hole for the Assembly – R19.95 from Paarl Build It  A lesson learned: the 15mm of particularly the brass nipple, I think refers to the inside diameter of the part. So when I got the 14mm drill bit (they didn’t have 15mm), I was 6mm off, because including the part’s walls and the thread, the nipple needs a 20mm hole. Serendipitously this wasn’t a train smash, because I could gradually carve the hole bigger, which helped me create a very snug fit – all the better to ensure water-tightness.
  9. Plumbers / Thread Seal Tape – R2.68 from Paarl Agrimark – Don’t we all have some of this lying around at home somewhere already? Will seal threads and such if there are leaks in any of the assembly’s joins.

All said, assuming you don’t destroy any furniture or kitchen surfaces in the making of this mash tun, it costs R324.29 in parts, plus the R19.95 drill bit, which you may or may not need (depending on the toolkit you already have).

How to Build Your Mash Tun

Step 1: Measure

To determine where to drill the hole, start with the brass back nut against the cooler box’s inside wall and find the lowest spot where the nut remains flush with the wall. If the nut lifts away from the wall because of that bottom curve, then you likely won’t be able to create a water-tight seal. When you’ve found the best position, use a measuring tape to determine the distance from the top of the cooler wall to top edge of the nut.

The measurement was started from the inside to find the ideal place for the brass back nut

Step 2: Mark

Apply the measurement to the outside wall of the cooler and mark where the top of the nut should go. Put a nut in place, and mark the centre of the nut. I coloured in the entire centre of the nut on the box to give me a good idea of how big a hole to drill.

Repeat the measurement on the outside, mark the spot and drill it

Step 3: Drill

Once you’ve established the centre position of the nut, drill the hole through from outside in, parallel to the horisontal. This Big Jim cooler box has 3 layers: a thicker outside plastic shell, styrofoam with ridges as padding in the centre and a much thinner inner shell. You don’t want to damage that inner shell, because if it tears or cracks you’re stuck with a leak. So drill slowly and with patience. I put the cooler box against a wall and gently, but firmly pushed against it as I drilled through at a very slow pace.

Step 4: Fit

With the hole drilled, make sure the brass nipple fits. If it doesn’t fit at all, use the drill bit to gradually grind away some more plastic. Do it slowly, keep the hole round and re-measure often – if the hole becomes too big or oddly shaped, you’re stuffed. If the nipple fits, but just too tightly, try screwing it in with gentle force. I did this, and the nipple’s thread carved away a tiny bit more plastic, creating a very snug fit. I also screwed in the nipple from the inside out, because done from the outside it will lift the thin inner lining, possibly stretching it, which could lead to a tear or crack.

The nipple screwed into the drilled hole

Step 5: Mount

I left about 3cm of the nipple on the inside and the rest on the outside. On both sides the back nut rubber washers went on first followed by the brass back-nuts, which were tightened sufficiently, without over-tightening them.

Inside nipple with the rubber backing and nut attached

Step 6: Attach

Complete the outside assembly by screwing the plastic nipple onto the brass nipple, and then screwing the tap into the plastic nipple.

Brass nipple with plastic hose nipple and tap attached

Step 7: Cut

Moving on to the braided metal hose, cut off one end. Some say to cut both ends, but I wanted to find another way to do this, because the fittings that came with the hose already perfectly fit the brass nipple .

Cutting the one end of the hose with some strong metal scissors is easiest (the wire cutting part of the pliers didn’t work so well) – garden trimming scissors also work.

Cutting the metal braided hose

Step 8: Perforate

Once I removed the one end of the metal braided hose, I took a small, but strong nail and about 2cm from the still-in-tact-fitting on the other side, worked my way in between the metal braiding, and perforated the rubber hose. Don’t damage the metal braiding, just work through it, and be sure to puncture the hose in a fairly straight line all around. You want to weaken the hose so that it snaps easily when you pull it out.

Step 9: Pull

I took me about 5 minutes to satisfactorily perforate the hose. Back at the already cut end, I carefully moved the braid down a little to expose some of the hose. I pinched the still in-tact fitting between my feet, and slowly started to pull the hose, at first with a pair of pliers. The hose stretched quite a bit while the metal braid moved down to expose more of the hose, which I could soon grab with my hands. Ever increasing the tension, the hose eventually snapped, as planned, along the perforation. I then just gently worked the hose out of the braid, leaving me with just the braided metal sleeve that will become the filter for my grain bed.

After the cut with the inside rubber hose removed

Step 10: Crimp

The cut side of the metal braid is dangerous and can’t remain open. So just fold it in on itself and crimp it with a pair of pliers so that it doesn’t a) let grain in and b) hurt somebody. Once you’re done, screw the fitting on to the exposed part of the brass nipple on the inside of your cooler box and voila! Almost finished.

Completed assembly inside

Step 11: Test

All that’s left to do is double check and retighten all the fittings and fill the cooler box with a bit of water to make sure it’s all waterproof as expected. I didn’t need to use any plumber’s tape, but if any of your joins leak, then apply the plumber’s tape judiciously.

Before you actually use your mash tun, be sure to clean every part thoroughly. Make doubly sure you don’t have any plastic, styrofoam or metal splinters hanging around or stuck in the metal braid.

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About Jaco Swanepoel

Jaco discovered craft beer and home-brewing during a trip to Singapore in 2009. After noticing SA's burgeoning craft beer scene in 2012, he accepted craft into his online life too, and started plotting his craft beer discoveries and adventures on CraftBru.com. He chirps and grams every now and then.

4 comments on “Build a Mash Tun for All Grain Brewing

  1. Harper - :

    Nice one! It’s about time someone did a local step-by-step build of the mash tun. Thanks for this!

  2. Ryan - :

    Keep us updated with your first Brew.

    • CraftBru - :

      Howzit Ryan, there’s been several since this post, but here’s the first one “Homebrewing a Robust Porter“. Kind of in-between brews at the moment, but will be getting back to it again soon.

  3. daafvader - :

    Awesome thanks for the info!

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