Finally I managed to find the time and gather the equipment to put together a shiny new stainless steel mashtun, and I’m very pleased with the results (although the first brew with the new beast will be the real proof of my amateurish construction skills.)
I bought a 50L stainless steel Thermobox from a German company called Nordic Optical around six months ago, since when it has been sitting about in a carboard box looking ominous and neglected. A Thermobox is a double-walled stainless steel vat with styrofoam insulated walls and a latch-locked lid. They are designed to carry hot food for function caterers, but can be (and have been) turned into fantastic mashtuns suitable for batch or fly-sparging just by adding a tap of some sort and a grain filtering device. My problem was to work out how to practically and affordably build a straining manifold (or false bottom) and fix a tap on to the thin twin walls.
I put the project off for some time not only because I needed the money to buy decent tools (especially holesaws) capable of cutting stainless efficiently, but also because I didn’t really know how to use the correct plumbing components and get the thing done without wrecking a valuable stainless tub. As it turned out, all I needed to do was buy some quality kit, digest a huge amount of valuable advice from homebrewers more practically minded than myself on JBK and latterly The HomeBrew Forum, then get a day off work and bite the bullet. Fortunately all went well.
I’ve attached a dozen or so photos of the process below which should be self explanatory. I began by making a mashtun manifold out of 15mm copper pipe and fittings. This is a tried and tested method of extracting the sugary wort from the mash and one that is still generally favoured over false bottoms among the UK brewing community, although I wouldn’t discount buying a US stainless FB one day if I’m lucky enough to get over there. I started cutting slots with a hacksaw and found it a complete nightmare, so after some advice I began using a Dremel 300 with cut-off wheels to cut as many slots halfway through the pipe structure as possible. The standard wheels managed about 15 cuts each before grinding down to nothing and shattering across the room, but I had more luck with the heavy duty versions (still burnt through about eight of these though!) Once done I had a nice size manifold with a lot of cuts. I realised I was maximising drainage while increasing deadspace with the extent of these cuts, but figured it would amount to no more than two litres which I would compensate for in future brewdays.
Cutting the actual Thermobox had been my biggest worry. Forums abound with tales of holesaws perishing on stainless walls and slippages wrecking that all important shiny surface. I bought the best quality holesaws I could source from a great traditional hardware store – Partridge’s of Hadleigh, Suffolk. The Bahco Bi-Metal Sandflex holesaws and arbours weren’t cheap but looked the part. Following the lead of other brewfacturers on the forums mentioned, I made a punchhole and then cut a 25mm hole in the outer skin as low down as I could to meet the internal floor. I made sure the arbour pilot drill pierced the inner wall so that I could then easily line up and cut a 22mm hole in the internal skin. So far, so good – the saws went through the steel like butter.
The next step was to fit the tap. I used the Dremel to take of any slight burrs then tried fitting the assembly. Essentially I was using a standard 15mm ball valve lever tap, a 15mm female-to female socket piece, a nylon/rubber washer and a standard 15mm tank connecter. The idea was to emulate a forum idea to leave the lip of the socket connecter outside in order to add strength to the tap connection, while its 25mm length body would span the void between the thin stainless walls and tighten to the tank connecter. In practice I had to Dremel off the lip ridge on one end of the socket connecter as well as two ridges on its body before squeezing it into the 25mm hole and fitting it tightly on to the tap (using synthetic lubricant) and into the outside hole. In order to allow the tank connecter to tighten properly from the inside, I then had to reduce its length by about 15mm and replace the washer before lubing up the thread and tightening until the walls pinched. It all looked great.
With the tap fitted I turned to the manifold. I had left a t-piece positioned at one end of the manifold grid and then attached this directly to the aperture on the back of the tank connecter with a piece of carefully bent 15mm copper pipe. The whole assembly not only comes apart for cleaning, it also pivots vertically around the t-piece, which is handy for removing moisture before storage. And that’s it really – it all looks the part. I have further plans to install a unique permanent sparging device into the lid of the tun so I can fly sparge without unlocking the tun at all, but more of that another day! Here are the pics.
Looks like a fantastic mash tun – all nice and shiny 🙂 How good is it in practice? Does it maintain the temperature long enough?
I’m seriously thinking about following your approach (thanks to your detailed process) when I step up to AG brewing.
Hi Warren. I think the thermobox is a superb piece of kit. For £40-£80 plus shipping (depending on size) you get a large, easy to clean vessel that holds temperature within a degree or two over a 90 minute mash and also looks and feels great to use. Obviously you need to put plenty of hot water in it ahead of a mash to bring the tun itself up to temperature, and there is the slight hassle/fun of making a manifold/false bottom and changing the tap, but you’ll be pleased you did it.
I must say though, that a plastic cooler from Igloo or similar will also do the job fantastically well and being plastic they are easier to adapt and work with. I had one of these with a plastic pipe drain manifold plus a sparge manifold in the lid and loved it. It was a little small and eventually got a bit tired, which is why I switched to stainless, but is a great, cheap optiion that doesn’t require bi-metal tooling.
Good luck in your hike to AG – I can’t recommend it highly enough.