Home Brew Equipment - Mash Tun

Our mash tun is made from the Coleman 45 litre cool box.  It was about £35 delivered in the UK from Simply Hike - not forgetting some cashback :)

The cool box comes ready plumbed with a value, which is more of a rubber stopper.  This was removed and replaced with a 1/2" ball valve from Screwfix.  The ball value has threads for compression nuts on either side suitable for 15mm pipe, but the thread is just long enough to push through the pre-cut hole in the cool box wall and allow a tank connecter nut plus a 1/2" rubber washer to fasten on the inside.  Tighten it up, then tighten it up some more, and you've got a water tight seal.

The only downsides to this valve/cool box combination are :

• The valve handle is too wide to allow the valve to close fully.  I had to hacksaw half the handle off so that it would rotate around enough.
• There isn't enough thread on valve on the inside of the cool box to securely fit a pipe, i.e. via compression fitting.  This wasn't a worry for us as our manifold simply slots in to the valve and doesn't need to be secured.  Because it's not an airtight joint though, there might be an issue with the syphon effect, but I've not noticed a huge amount of deadspace - more on that later.

Next up is the manifold that allows the wort to escape the mash tun.  The manifold is simply lengths of 22mm copper and 22mm end feed elbows and tees.  Everything slots firmly together without the need for any soldering or securing.  The pipe has slots cut in to it at 10mm intervals; the slots are cut to half way through the pipe.  The slots sit facing down against the bottom of the cool box.  The idea is that the grain acts as a filter and the manifold stops the larger bits of grain coming through.  In reality it takes about 6 litres of run-off and return before the grain-bed is settled and the wort is clear enough to transfer in to the boiler.

Here's the manifold as it would sit in the mash tun.

And upside down to show the slots

Finally there's a 22mm x 22mm x 15mm reducing tee to accommodate a small curved length of 15mm pipe to connect the manifold in to the ball valve on the inside of the mash tun.  The manifold sits flush on the bottom of the cool box.

When we tested the mash tun's heat retention with hot water we found it was loosing between 5°C and 10°C over a 90 minute period.  The heat retention of the water and grain mix should be much better than just water by itself, but just to be sure we took four extra steps.

• Always preheat the mash tun with boiling water from the kettle about an hour before the mash tun is needed, then discard the water.  The cold manifold and inside walls of the cool box takes a lot of heat out of any hot water that is added.  We also tend to add the mash water at a temperature about 10°C above the strike temperature and allow the water to cool.
• The lid is hollow, so we drilled 10mm holes in the top of the lid and filled each hole with as much expanding foam as we could.  The lid is now much heavier, although we're not sure it's made a huge difference to the heat retention.
• There is a lot of head space in the mash tun for a 11 litre mash, so we lay a sheet of kitchen foil on top of the grain to try and reflect as much heat back into the mash tun.
• We wrap the mash tun in a Wickes cylinder jacket - the four lengths of insulation inside red plastic - for the duration of the mash.

The mash tun holds to within 1°C over a 90 minute mash.

The only other thing we do is to put an Argos catalogue (or any other book/object that is about 2" thick) under end of the mash tun to tip it towards the valve end. We batch sparge and allow for 1 litre of deadspace in the mash tun when calculating our batch volumes.

More pictures here.

Dave & Suki.