About 4 years ago I decided to take up brewing my own beer as a serious hobby. By ‘serious’ I’m not talking about the 12% ABV gut-rotting death ale that many associate with homebrew, but brewing beers with faithful attention to style, strength, flavour and aroma. Beers that would stand up to my favourite commercial bitters, pale ales and stouts in terms of both taste and finish.

An early decision I made was that I wanted to brew straight from malted grains (barley, wheat, etc) rather than using tinned or powdered malt extracts. Extract brewing is perfectly respectable and a great entry-level way to start, but I felt it suited me more to dive straight in at the complicated end. However, choosing the all-grain route left me with an important requirement, I needed a ‘mash tun.’

‘Mashing’ is the term that brewers give to the process of steeping malted grains in water at a specific temperature, activating enzymes that convert the starch in the grain into fermentable sugars. The ‘mash tun’ is the vessel in which this steeping takes place for a duration of 90 minutes, so to hold a body of liquid at such a defined temperature for this length of time would obviously require something with significant insulation. What better vessel than a picnic cool box? Just as suitable for keeping a mash at a stable 64°C as it is for keeping sandwiches and salads chilled. My cool box is a Thermos 32 litre ‘Weekender’ - the Rolls Royce of cool boxes - easily capable of mashing 5 kilos of grain, enough for a 25 litre batch of the good stuff.

A couple of modifications are needed before she’s ready to go. A keg tap is core-drilled into the wall of the cool box, behind which a run-off manifold is fitted. The manifold’s job is to allow the wort (brewspeak for unfermented beer) to pass freely through the 5 kilos of grain to the tap without getting bunged up along the way, an unfortunate event known as a ’stuck mash.’ It’s made from standard copper plumbing pipe and the elbows and T-joint are solder fittings so a quick blast with a blow torch was all it took to fix it together. The crossbeam is there to increase the surface area of the manifold and the outward-turned T-joint attaches to the back of the keg tap via a hosepipe fitting and a short length of syphon tube. Finally, slots are sawed into the bottom of the manifold at 10mm intervals, at a depth of just less than half the pipe’s width. My Dad and I worked up a hell of a sweat with our junior hacksaws that day, I can tell you. Good thing we each had a bottle of Deuchars IPA to hand.

And so, tap and manifold firmly in place, (slots facing downward) the mash can begin. Water is heated in the boiler to ‘strike temperature’ (calculated to several degrees higher than the intended mash temperature, accounting for the loss of heat when the grain is added) and the grains are stirred in well to avoid clumping. If the mash temperature hasn’t been hit then either more hot or more cold water can be added to adjust. With the room already filling with a malty aroma like a cow biscuit dunked in a mug of Horlicks, the mash tun lid goes on and the whole thing is wrapped up in a thick sleeping bag for extra insulation. An hour-and-a-half later and the mash tun will be full of sweet liquid maltose (and other sugars) that the brewer’s yeast can go to town on. Mashing is only the first step along the way, of course, but one made so easy by this little DIY gem.

The bottom line is that you can mash in anything, but this set-up is extremely efficient (I’ll barely lose 2 or 3°C over the 90 minutes) and is ideal for the batch sizes I like to brew. Ladies and Gents, the cool box mash tun. Its inventor, whoe’er you may be, I salute you!

GDave