Small False Bottom in Huge Mash Tun. Efficiency Woes?

[BudzAndSudz]

Ok so I used to mash in a 10 gallon igloo cooler which worked great for 10 gallon batches. However, I recently built this beautiful son of a gun;

Thing is, it's got a 25 gallon mash tun, and I'm still using my 10" false bottom from my igloo cooler. Last night I made 15 gallons of a 1.090 English Old Ale and the weight of the grains during sparge actually deformed the false bottom and nearly crushed it. Of course, this prevented it from working and I got the most absurd stuck sparge in the history of brewing. Everything in my system got clogged with grain from my hosebarbs to my pump and it took me a solid 45 minutes to get it all out. Don't think it affected the beer but man was it annoying.

On smaller batches though I'm still thinking I get poor efficiency because a 10" filter screen on a 22" wide pot seems to just encourage channeling because the drain area is so small. All the water is pulled towards the center instead of getting a nice even flow throughout the grain bed. Is there any validity to that theory?

I guess my question is what my options are. Does someone make a 20" false bottom? Will that actually help my efficiency, or will it just prevent it from crushing my false bottom? Also, I'd really like one with a 1/2" hose barb, the 1/4" one I have now is the biggest limiting factor in my system right now.

Thanks!

 

[eastoak]

http://www.norcalbrewingsolutions.com/store/False_Bottoms_Other_Custom.html

one idea, there are probably others you can buy. if you are handy you could make one too.

 

[BudzAndSudz]

Do you think it will actually help with efficiency or will it just be stronger?

 

[Bobby_M]

It looks like you are running HERMS so it's not a great idea to try to pump recirculate with such a small false bottom. There just isn't enough surface area to support that kind of flow. As you've discovered though, 22" false bottoms are not cheap. While it's not ideal, I can tell you that cutting a circle out of a 24x24" piece of perforated is possible with a thin cutoff disc on an angle grinder. Also, once you get to this size vessel, you'll find they are never perfectly round so don't expect to get an edge-tight fit. I've had best results by cutting it small enough to drop in, then scribe the exact circle by spacing a sharpie 1/4" away from the wall. Then line the edge with a silicone edge gasket with a wiper. Mcmaster.com has it. Spacing the FB off the bottom is a trick too. You can drill a bunch of holes in the FB and use stainless 1/4-20 bolts and nuts as standoffs.

 

[BudzAndSudz]

How important is it to have it be an exact fit? I'm assuming the bigger the better?

Also I really like the thought of the silicone gasket to help seal the bottom, forcing flow through the strainer portion rather than under and around.

 

[Bobby_M]

When you use a flat disc, fit is very important. When they are domed, the seal is made to the bottom of the pot.

 

[BudzAndSudz]

My one last question; I used to dough in, then let the mash set for 10 minutes to establish the grain bed because I heard that immediately starting the recirculation would lead to channeling and decreased efficiency. If I'm working with a full sized FB is that step still necessary?

 

[eastoak]

My one last question; I used to dough in, then let the mash set for 10 minutes to establish the grain bed because I heard that immediately starting the recirculation would lead to channeling and decreased efficiency. If I'm working with a full sized FB is that step still necessary?

you don't but i find that it works best for me if i do wait at least 5 min or so before starting the recirculation.

 

[BudzAndSudz]

What sort of efficiency are you getting? I'm still getting around 70% or so on this system which is basically exactly the same as my cooler MLT got. I hear that's unusual so I'm trying to figure out the best way to raise my efficiency.

 

[SavoryChef]

I have 25 gallon pots and just switched to batch sparging and went from 65%-70% to almost 80% . The deadspace in those large pots leaves a lot of usable wort

 

[BudzAndSudz]

I always batch sparge. My tiny false bottom leaves very little excess wort as well so I'm fairly confident those aren't the causes.