False Bottom

Not the latest fad from the plastic surgeon, but rather a device for efficient lautering (draining) of the grain bed. Up until now in my brewing I have been using a small coolerbox, the argos type, 24L I think. And it has served me well, but everyone knows that home brewing is like an arms race that you run against yourself, or perhaps your daydreaming imagination. In any case, I recently bought a Coleman 48 quart (45L) coolbox, and I decided I would up the lautering device to match. I had been using a simple copper manifold, but I though that what I now needed was a full stainless steel (= shiny) perforated false bottom, like this one.

First port of call was Ebay, where I bought a sheet of perforated stainless steel, 1.5mm thick, with 3mm holes. I am stillplan slightly concerned that 3mm is slightly too big, but I have confidence that the grain bed will act as a reasonable filter.

I decided that the false bottom would have a centre ridge, 7cm from the bottom, sloping on either side down to the edges. I had been worried that 1.5mm would need extra support, but it’s no problem, the whole thing is perfectly stiff and rigid. I would leave triangular ‘tabs’ at either end to fold down to create the ends, as you can see from the plan I drew out on the sheet. Figuring out the dimensions from the size of the floor of the cooler was a simple matter of applying Pythagoras’ theorem.

linesI initially tried to cut this with a jigsaw, first on a high speed, then on a low (after reading metal should be cut on low), but to no avail. I burned through several blades before resorting to the angle grinder. I don’t know why I didn’t in the first place, I think the angle grinder scares me, it is brutish and aggressive. It sliced through the sheet like a hot knife through butter though. 10 minutes later I had the cut out sheet, waiting to be bent. cut

1.5mm steel doesn’t actually bend that easily, and I tried a couple of methods, eventually settling on a kind of sandwich-clamp affair. Clamping some wood on either side of the line allows you to slowly put pressure on the steel and get an even bend along the line. Towards the edge it kind of flared out a bit, but this was easily remedied by holding it in a vice and giving it a few bashes with a hammer.

For the centre, I clamped scrap wood on either side of the centre line, and kneeled on one side while I pulled the other towards me, which worked well. Here are some pictures of the bending process and the finished bend.

bendingcentre bendbentfinished bend

Once the bend was finished, I realised I’d need a hole for the brass threaded tube that forms the back of the bulkhead (tap) to fit through. The idea was that some tubing would sit roughly in the middle of the floor under the false bottom to act as pickup, and the screen would have a hole that sat over the tube and the brass. I cut it with my dremel, going through about 3 of those little disks, and it’s not pretty, but hey, I’m not a metalworker. hole

Once all that was done, I checked to see if it fit, which it did. I ‘tied’ the ends together with a small piece of wire, just to keep the ends tight together, since there would be a gap where grain could get through at either end. I also thought that it would be a good idea to put some tubing, the same as the beer line that we normally use for siphoning etc. around the edges, for two reasons. tubingFirstly, even though I had ground off  the sharp edges with the grinder, because it was perf sheet it was still quite jagged. Secondly, I thought the rubbery ‘cushion’ would ensure that there was a snug fit between the false bottom and the base of the cooler, important to stop particles getting into the wort. I sliced some old tubing open with a scissors, and attached it using little plastic cable ties. Here is the finished product. I will post its efficiency as soon as I test it.

completely finished



Filed under equipment

6 responses to “False Bottom

  1. Very nice work with the false bottom.

    • stoutfellow

      thanks! I’m thinking i’ll need a fairly big beer to use this mash tun though. I’d say it will need at least 6 or 7 kg to make the grain bed deep enough.

  2. Pat

    Nice job. How did the 3mm holes work out?
    I’m looking to make a false bottom for my own MT albeit a round one.

    • stoutfellow

      Thanks. They actually worked out fine. Originally I was running a 3/4 inch plastic (similar to a siphoning line) pickup tube from the inside of the tap to about the centre of the box, so as to be drawing from the middle, but it had a tendency to block up. Whether that was from stray grain clogging I don’t know, but I suspect that since those plastic tubes get very soft and rubbery when heated, the whole thing may have been compacting. Now I use no tube, and it’s fine. Admittedly I haven’t done a beer with a high wheat content yet, but I have done ones with wheat flour added to the grist, and no problem. I recirculate the first 2 litres or so, and it seems pretty clear runnings after that, especially if I leave it a couple of hours before draining. I think once the liquid drawing compacts the bed a little, no particles tend to come through.

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