I saw Deebee's chopping board false bottom mash tun a while ago and wanted to have a go myself. I loved the idea of using something as cheap as a chopping board, the simplicity of design and the improved efficiency it promised, as well as the robustness and the fact that there are no pipes to knock off with a stirring spoon. My dream was to have a false bottom I could just drop in and forget; one that fitted so well I wouldn't need to worry about sealing around the edges. Fired up with the giddy hopes of slightly more efficient sparges, I bought a chopping board from Tescoids for about 4 quid, marked lines on it, cut it to size and started drilling...
626 two millimetre holes later and I had a false bottom that didn't work very well. Sure, it fitted tighter than some sort of obscene thinly-disguised sexual reference, but it had problems. Big problems. First, it floated; grain sinks but the bottom floats - a false middle isn't much use. Second, there was a big gap at one end where the handle was. I was going to make some sort of box to cover the gap, surrounding the hole where the outlet is, but with the added problem of anchoring it down, the whole thing was starting to look like a pain in the bum.
But what killed it off was the warping. I had bought two chopping boards, one for me and one for the house (you see? I don't just think of beer all the time), and after a couple of goes in the dishwasher the house one resembled a large soup bowl. Drill 626 holes in it and it gets worse. And you've got soup all over your feet. If you then counter-bore the holes out on one side to improve the flow, you get a very sensitive thermometer; if it gets even slightly hot it almost folds itself in half. I did actually fix the problem by counter-boring holes the other side too, but by this time I was out of love with the whole chopping board/false bottom thing and looking for my new sweetheart, in the shape of a copper sheet.
You can buy copper sheet on Ebay but Dennis can also get you some. I'm not sure if all Dennises can do this, but mine can and he did. Generously waving away any suggestions Dennis made of remuneration, I got to work. Here it is, cut to size and dropped in the mash tun. Amazingly, I had enough foresight to drill a big hole in the middle to stick my finger through in order to get it out. If I hadn't done this, I would have had to shake it out each time it jammed in while I was getting it to fit, probably losing at least one toe at some point.
And so on to the holes. Anther 626 of them in copper, which is pretty grim to machine on account of it occasionally grabbing hold of the drill and snapping it. Using the chopping board as a guide to drill through and plenty of cutting fluid, I did it with only 2 drills.
I attached feet (15mm end feed caps) and the inexpertly soldered outlet feed. It hoovers up the liquid to a depth of a mere 2mm from the bottom of the tun.
So here is the false bottom, fully assembled and in place. It's pretty and you can whack it with a spoon all day without any bits dropping off.
This is the volume of the dead space:
What could go wrong, other than the difference in thermal expansion rates of copper and plastic causing a large gap to open up on two sides of the false bottom when mashing, letting grain through but more importantly, providing a channel for the sparge water to flow down rather than forcing it through the grain, washing it out as it is supposed to do? So much for the nice tight fit.
Luckily, JBK forums have people who know everything, including where to get food-grade high temperature silicon rubber sheet. A quick wibble on Autocad later, and I've got the template for a large washer to go round the outside. Some chopped up silicon rubber, copper strips and some more drilling later...
and it seems to fit, even with a kettle-full of hot water in it. Hooray! I just need to try it out now. It's 12 days to the next brew day and I'll post an update on how it performed after that. It'll probably explode in my face or burn the house down or something.
So what have I learned, having spent so much time drilling 1,304 holes in things and then swearing at them? Firstly, any more problems and I'm going back to the 15mm pipe manifold filter. It wasn't that bad and ruthless efficiency isn't everything. Secondly, if you are making something, don't bother about accuracy - just fill in the gaps with bits of rubber. And thirdly, don't start making lists of things you have learned if you have only learned two things; you can probably come up with some sort of humourous item to tack on the end but it won't really work.
Nice piece of workmanship too!
