Troubleshooting Mash Tun Issue

[edramshaw]

I was hoping to get some other thoughts on this problem I have been having with my new mash tun. Its a converted keg with a 12" SS perforated false bottom that just sits on the bottom of the keg and a dip tube that extends down into center of the FB and draw from there. I have a single tier system and use two chugger pumps to move liquid around.

The problem: when I recirc the liquid will stop flowing after a while. The pump is still spinning but the liquid is not moving at all.

Attempted solutions: I am able to get it going sometimes by blowing back through the pump to the bottom of the mash tun although this doesnt always work. I notice sometimes bubbles will rise up through the mash (not while I am blowing by while the pump is shut off and I am trying to get the thing going again). MY thought was that the FB might have been bowing in the center and causing it to seal up on the bottom leaving it no place to really draw liquid from. I was all exciting that this would solve the problem so I put 2 3/4" SS nuts on the bottom near the dip tube to give it support in the center. Unfortunately this didnt work. Granted the next batch I did was an Imperial IPA so I had 40lbs of grain in there. (Didnt think that one through but damit I was sure).

Some observations:

When it stopped on this last batch I found that if I brought my heavy duty stainless steel mash rake to the bottom of the mash and scraped the grains off the bottom I would see those bubbles again and the pump would start pumping again.

When I blew back through the pump and into the mash there was little to no resistance.

When I cleared out the grain from this last batch and removed the FB I noticed that at the level the nuts were at there was maybe enough room to accommodate maybe 3/4 cup of liquid.

My thoughts now are that the collection space from below the FB is too small and it is creating a vacuum which is then sucking wet grain into the perforations and blocking the ability of the liquid to flow through. Does this make sense? I've read about other people doing it this way with success so I am not really sure. If this does look like the problem does anyone have any suggestions for ways to lift the false bottom off the bottom? Thanks!

[ajdelange]

My thoughts now are that the collection space from below the FB is too small and it is creating a vacuum which is then sucking wet grain into the perforations and blocking the ability of the liquid to flow through. Does this make sense? I've read about other people doing it this way with success so I am not really sure. If this does look like the problem does anyone have any suggestions for ways to lift the false bottom off the bottom? Thanks!

It does sound as if you have the old 'stuck mash' problem. Hypothesis: you are drawing out from under the screen and the grain bed is compacting down upon it as you do so to the point where the screen gets sealed. The more the pump draws, the tighter the grain gets packed down onto the screen. This usually happens in the lauter tun but if I understand the setup correctly there is no reason it couldn't happen in the mash tun too. The usual solution is rice hulls which keep the grain bed from compacting.

If you want to raise the false bottom some what you are already on the right track with the nuts. Get some accompanying bolts (stainless), drill three or four holes in the false bottom, put the bolts through and use a jam nut on the top of the screen and another nut on the bottom. With this arrangement you can adjust the height of the 'legs' and set the level of the false bottom wherever you like (limited by the length of the bolts).

[spiderwrangler]

If you want to raise the false bottom some what you are already on the right track with the nuts. Get some accompanying bolts (stainless), drill three or four holes in the false bottom, put the bolts through and use a jam nut on the top of the screen and another nut on the bottom. With this arrangement you can adjust the height of the 'legs' and set the level of the false bottom wherever you like (limited by the length of the bolts).

The ability to do this would likely depend on how the dip tube enters the screen, and whether the screen is the full inside diameter of the keg. What are doing with your recirc? Do you know your flow rates on your pumps?

[PSUHomebrewer]

Is your fb domed? Ihave a 9" fb in my keggle and believe I leave more than a cup of liquid there, and there was alot more when I used my 12" cooler fb in the keggle. It may seem weird but if the screen is domed that it is sitting dome up.

[ajdelange]

The ability to do this would likely depend on how the dip tube enters the screen, and whether the screen is the full inside diameter of the keg.

Good point. Guess it would work fine with the newer straight sided design but the old barrel shaped ones probably not.

Here's what I am talking about. It fits in a 15 gal Volrath stock pot. I used to use it for lautering. It still serves for steaming crabs. http://www.pbase.com/image/141669522

[Monster Mash]

I had the same problem with my false bottom years ago, since switching to a braid I have never had a stuck mash....

[cornhole]

Two thoughts: (1) Try doing your re-circulation without the grain. (2) Throttle down the output of the pump. The flow could be strong enough to pack all the grain down, essentially sealing up the false bottom.
MY $0.02

[edramshaw]

cornhole: Did that, worked fine without grain. Throtttling had no noticable , i.e. it is possible it bought me a minute but in the end it still stopped