If, like me, you're a homebrewer who uses the same pot for mashing and boiling, then you may have experienced heat loss during the mash that you'd rather didn't happen. This tends to be a problem for smaller batches, or when brewing outdoors in the colder months.

My solution was to make this 'tun cosy' (or I suppose tun cozy if you're in the US), an insulating jacket for my brew pot, which I can slide on and off. I now lose only 1-2 deg C per hour while mashing batches as small as ~2 gallons, and that includes lifting the lid to check on things.

The design uses canned expanding foam, commonly used to fill large gaps in walls for DIY etc. This stuff has excellent thermal insulation properties, and as such it's often used in large quantities to insulate cavity walls in houses. Actually it's similar to what you find around hot water tanks (so it must be good!). Best of all, it's readily available, easy to use and cheap. This whole project cost me £10 (approx. $15), and most of that went on buying a huge plant pot.

In a nutshell, you're going to wrap your brew pot/kettle in aluminium foil, suspend it in a larger container, and then fill in the gap with foam. When the foam goes hard you'll have a tailor-made, removable insulating jacket for your pot.

I tend to brew ~8 litre batches so my pot is quite modest (15 litres), but there's no reason this can't be done for much larger pots, providing they have straight sides and you can find a big enough bin to contain the foam.



UPDATE 2014-03-19: I just had an idea for people with large pots, or who have pots with spigots, or who don't want to lift a heavy pot full of mash: once the foam has set then you could simply slice the whole thing in two. Then, instead of lowering the pot into the tight space, you can bring the two halves of the foam in from opposite sides and hold the whole thing together with a strap. See new step 6...