Poster Child For Grain Bed Compaction: Collapsed False Bottom

I was in the habit of running a recirculation mash with the pump valves wide open. I always thought if the mash stuck, you can just stop the pump, stir the mash, and continue on with the recirculation...right?...until my false bottom collapsed (see pic) and I had to totally empty the mash into another vessel and jury rig the false bottom, just to get through the brew day. This happened on 3 batches, generally when the malt bill exceeded 30 lbs, all barley malt. (15 gallon mashtun, 11 gallon batches, as close to 1.5 quarts/lb strike water as I can get). 0.039 mill gap.

So what is happening? Pump suction due to grain bed compaction? Weight of grain and water exerting force on the legs of the false bottom? Combination of the two? Any ideas?

Possible solutions that I've considered:
1. Reduce recirculation flow, valve half open. This reduces temperature response of the system, but it beats the schmitt out of emptying my mashtun and hammering my false bottom back in shape.
2. Reinforce/add supports for the false bottom. Any ideas?
3. Increase the gap on my mill to get a more course crush...0.045? My mash efficiency isn't really all that great to begin with (~0.80), but willing to try it to avoid another FB collapse.
4. Add rice hulls to the grain bill...hate that idea...no one else I know does that unless the grain bill is 50% or higher in wheat or rye, or god forbid...pumpkin...
5. Limit my grain bill to less than 30 lbs of grain. Reduce batch size to maintain SG.
6. Add a suction gauge to the outlet of the mash tun so I know when a vaccum is forming, stirring mash if required.

Other ideas?
Anyone with a similar experience?
What worked for you?

Any help is really appreciated...

 

Ouch. Um...yeah...I'd definitely add quite a few more supports. Get some stainless sheet metal screws and acorn nuts and use the screws as supports. I'd probably use 3 or 4 for each collapsed section.

 

you need jay birds false bottom supports!!

 

I have a very similar setup and cannot imagine how this happened. I can literally stand on my FB without it bending (I weigh almost 300lb). If it were a weight or suction thing, I would have expected the perforated metal to collapse, not the handle/supports. That is bizarre.

 

daksin: the center of the perf sheet actually did collapse in the middle, causing the edges to raise up and allow the mash to bypass the screen, in addition to the legs collapsing...you can see it in the photo...hard to imagine that kind of force coming from a March 815 pump...

 

I'll check them out...sold by Nor Cal, right?

 

Sheet metal or machine screws? do you have a photo of an installation like this?

 

Just guessing at the size of yer rig but if the false bottom is say 16" diameter that's about 200 square inches. It wouldn't take a whole lot of psi to add up to a serious load quick. I'd throttle that recirc back.

 

With the FB fully plugged up, a pump can pull 1000 pounds on an area that big.

 

Yup. That collapse was totally due to pumping with a plugged FB...

Cheers!

 

Throttle back, even several pounds per square inch of suction over several hundred square inches is many hundred pounds exerted on the FB!

 

I started bending the FB support legs back in position...looks like schmitt...and wobbles, so I decided to start over with a new FB with a center support. Also have a suction gauge for the MT discharge on order.

Thanks everyone for your observations and suggestions, you've all been very helpful...and sometimes misery likes company...

 

Wow good to know! I occasionally have something like that happen on my big system and now I know not to treat it lightly. Great info in this thread.

 

Added the suction gauge a few weeks ago and brewed a couple batches without getting a twitch...I was thinking it was total overkill...until the last batch over the weekend. 40% corn and rice adjuncts, 60% 6-row...stopped stirring for 5 minutes to get a cup of coffee...come back to a compressed grain bed, zero recirculation and 2/3 DEFLECTION ON THE SUCTION GAUGE! It worked! Finished the mash and lauter...cleaned the mash and found no deflection or damage to the false bottom! Maybe not overkill after all...

 

Great fix man that's KILLER. If you decide in the long run you do need a stand PM me I can custom build you one that will work UNDER your false bottom as it sits and save you from having to replace the screen any time soon. Our stands also add a boatload of extra filtration.
Cheers
Jay

 

Jaybird, I have a false bottom just like the one the OP has indicated. How would you fix this and about how much would it cost?

 

All I would need is an exact height to the bottom of their false bottom and I could build a very simple stand to go under it. Cost? Let me check real quick and get back to you. Give me a few.

Cheers
Jay

 

$29 bucks. It would be a simple X that would go under the false bottom and between the stands you already have on the false bottom.

Cheers
Jay

 

Added a cross brace under my false bottom for a mash last week...worked awesome! Thanks for the advice Jaybird...Might seem like belt and suspenders, but if you've ever had to recover from collapsed FB and a 15 gallon compacted grain bed, you know that $29 is a bargain for the insurance...Brew Dog stood guard over the operation to maintain security...

 

SWEET! Glad I could help.. Looks killer in the kettle BrewGeek . How was the height?

Now send me samples JKJKJK..



Cheers
Jay

 

The height looks perfect to me...about 1/16" under the FB...

 

Looks like we nailed it man! I love to see a plan come together! I think once you use it a few times you'll ask yourself how you ever lived without the added filtration. The stability is just a bonus!

Cheers
Jay

 

I guess I'm a little late to this party, but you could also have fixed this problem be adding a simple grant to your setup. You'd drain from the mash tun into the grant by a simple gravity feed, then pump from the grant back to the tun. This would eliminate any suction from the mash tun altogether. It also gives you a good point at which to evaluate the wort clarity during recirculation, not to mention take samples to test for starch conversion and monitor wort pH.

 

kombat - Adding a grant is for sure another way to skin the cat...that's a great suggestion...Thanks!