Would a slotted false bottom prevent uniform compaction better than a perforated false bottom?

See this model: http://www.homebrewing.org/12-Stainless-Steel-Domed-False-Bottom_p_1058.html

I'm researching parts for my first all-grain mash tun build. My intent is a round 10-gallon beverage cooler using a false bottom. All false bottoms I've come across are the round perforation type, except that one.

The only advantage I can think of with this slotted false bottom is that it might prevent uniform compaction. Maybe it would be less resilient to channeling, but it seems that's the compromise of the design if I understand the issues correctly.

  • That page also claims "The 16% open design contributes to better efficiency and a clearer sparge". Better efficiency compared to what? Is this marketing gibberish or is this a valid claim over a principle I haven't grasped yet? Jan 29, 2012 at 20:48

3 Answers 3


The principle of the false bottom is that it makes the distance to the drain and the effort needed by the liquid to get there more uniform compared to other designs, such as a hand made manfold or a bazooka screen. This is mainly a concern if you are fly sparging.

I use the blichmann false bottom, which looks very similar. Compared to my old brewery with a hand-made manifold, extraction efficiency went from 70% to 90%. There were other changes, such as using recirc pumps, but I'm pretty sure the false bottom does contribute to that increase.

  • Are you using the Blichmann false bottom in a Blichmann pot? I've seen those but it wasn't clear if they would be appropriate for a 10-gal cooler MLT. Jan 29, 2012 at 21:44
  • I'm using it in a blickmann pot. They're more expensive than the one you listed, so I'd go with your find - it looks good. The blingmanns' false bottom is purpose built for their kettles.
    – mdma
    Jan 30, 2012 at 19:37

Compaction is a function of speed during draining and resistance of the "filter". A perforated false bottom offers less restriction than the slotted one. But the compaction is just a function of how hard you are pulling out of it, which is entirely managable with the valve out of the tun (or off the pump if that's your thing.

I recently upgrades to a perforated FB in a keg, and recirc with a pump through the mash. As I was working to regulate my temperature I noticed that the grain bed was pretty firm. I re-stirred the mash and slowed the flow a bit more with the ball valve, after that the mash was still pretty fluid. Its only the third batch with the pump set up in my rig so I am still adapting to how it works. I hope my example sort of demostrates that its more of a flow rate thing than a manifold thing I suspect.


I don't think it's an appreciable difference between slots and holes, but the slots let a slightly lower volume of liquid through, since there's less surface area opened up. If you're doing a recirc system, that might not be desirable as it could restrict your flow, but if you are fly sparging, that might be ideal.

In theory, if less liquid volume passes through the false bottom, the wort would probably be better filtered, but I can't imagine it's to a significant, or even noticeable, degree.

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