SERIOUSLY stuck sparge in new mash tun

[izg]

Hi all,

So today I fired up my new 82l system, planning to start gentle with a 69l batch of porter (3 times my usual quantity).

All went beautifully, hit mash temp etc etc, until the end of the mash, when I started recirculation (plan being to recirculate just for 5 mins or so to help clarify the wort). Anyway, basically no wort came out. Gave the whole thing a stir, even though I'd just added some water to bring up the temp for mash out, and still nothing.

In desperation, I poured out the whole mash into buckets and poured as much as it would take into my old, tried and tested, cooler mash tun. Still no joy. Vigorous stirring allowed a little wort to flow, but I mean, really a little.

In the end I used a sieve - even then it took a lot of shaking to get the wort out - and didn't even sparge, figured I'd just make less beer and cut my losses.

So - diagnosis! I would obviously blame my new DIY mash tun false bottom (pizza tray with holes, dip tube through the middle) except that the grain didn't work in my old mash tun either, and when I examined the false bottom assembly afterwards, there was no sign of blockage.

So could it be the grain? I'd just ordered new grain, and it's possible it came milled a little finer than usual. However, 10 of the 15kg of grain was from the end of an old sack, which had presented no sparge issues before. Would 5kg of too finely ground grain in a 20kg grain bill cause such a stuck sparge?

Really keen to get some opinions on this!

Iz

 

[LarMoeCur]

Pump or no pump? How are you supporting the pizza tray mash tun?

 

[Schreiner]

I would blame the pizza tray off the bat, but with sparging not working out in your old mash tun either, I would say too fine of a crush could be the culprit. Are we to assume this is an all barley malt grain bill?

It's good to have a bag of rice hulls around for situations like this. Pretty cheap insurance.

Adding some bolts through the pie plate around the center could insure that the false bottom won't collapse.

 

[GoeHaarden]

What was your grist ratio?

Get yourself a BIAB bag and line your mashtun with it (and on top of the false bottom). Never again a stuck sparge...

 

[izg]

Pump, but I would definitely rule that out because I stopped using that ASAP..

Yes, all barley. Bolts through the false bottom are a good idea, will definitely do that before next time to make sure collapsing isn't the problem.

The ratio probably didn't help - just over 2l/kg, rather than the 3l/kg recommended ratio. HOWEVER, after pouring the mash into my old mash tun, and it not working there, I began taking grain out with a sieve, until the mash became very thin indeed. Still no joy there, even with stirring, and no blockage in the manifold (which is what my old mash tun has). I assume a very floury ground malt could do this?

 

[Smellyglove]

The pump might be the culprit actually. Thick mash, and if you ran it full speed, and full speed is to much for your FB, your could have just compacted the maltbed enough.

 

[izg]

The pump might be the culprit actually. Thick mash, and if you ran it full speed, and full speed is to much for your FB, your could have just compacted the maltbed enough.

I would agree, except the pump only ran for a second or so before wort stopped coming through. Definitely no time for grain bed to be compacted, plus I then stirred it A LOT, then transferred to another mash tun, all with no pump. So I think we can categorically rule out the pump as the problem, even though I agree that in general a full speed pump could be a problem.

 

[LarMoeCur]

If you ran a pump and did not have the pan supported it for sure collapsed. There are plenty of pictures on this forum of mangled false bottom that had supports. Once that vacuum is created, all the particulate matter fills the holes like concert. Even if you remove the pump the holes are still plugged. Pump vacuums can generate a lot of force wedging the grain in place.

It only takes second for the pump to create a vacuum. Especially, if the weight of the grain and water has already pushed the false bottom down.

 

[izg]

If you ran a pump and did not have the pan supported it for sure collapsed. There are plenty of pictures on this forum of mangled false bottom that had supports. Once that vacuum is created, all the particulate matter fills the holes like concert. Even if you remove the pump the holes are still plugged. Pump vacuums can generate a lot of force wedging the grain in place.

It only takes second for the pump to create a vacuum. Especially, if the weight of the grain and water has already pushed the false bottom down.
View attachment 562056

That seems very likely tbh. Mine has the advantage over the one in that photo in that it has sides, so has inherent stiffness. Still don't think that was the whole problem tho.

 

[LarMoeCur]

How much dead space do you have under the pizza tray false bottom? Where is your dip tube located? What is your pizza tray made of? What is the mash tun made of?

Without supports, I'd bet you have about 1/2 gallon or less under the pan. Not sure what pump you are using but most are around 7 gpm. So, in 4 seconds the dead space is empty and now you have 1/20th of HP mechanical pump creating vacuum. Completely capable of collapsing your pizza pan false bottom. Mechanical pumps have one the highest vacuum factor and the effect factor curve is large. It's been a long time since I've done the math but we are talking about a lot of PSI worth of force.

 

[seatazzz]

Two things....get a ball valve on your outlet from your mash tun so you can throttle the flow. Also try lining your mash tun with a bag (wilserbrewer or your LHBS should have something similar, make sure you measure your mash tun to get the right fit). Advantages are no stuck mashes and cleaning your mash tun is literally a snap. Dump the spent grain out, rinse the bag, hang to dry, then once dry snap it a few times and it's perfectly clean and ready for next brew day. I have a store-bought false bottom AND a bazooka in my mash tun (with a bag) and haven't had a stuck mash or sparge in a long time.

When you're recirculating you need to throttle the flow to avoid creating the dreaded compacted mash bed and vacuum. For a standard ball valve, about 1/4 turn does the trick.

 

[RoadKing]

A couple things to try..Do not run the pump when mashing in. It will just pull the starchy flour down into the holes and efficiently plug them.
Also, don't run the pump for the first 10-15 minutes. Give the starches time to break down into sugar, which will be more fluid.
Unconverted starch is like paste and will clog anything. Then pulling against it with a pump will result in a stuck sparge and or collapsed bottom.

 

[Bobby_M]

Diptube bottoming out on tun floor? Cut shallow slits in bottom opening or slight angled cut.

 

[Smellyglove]

A couple things to try..Do not run the pump when mashing in. It will just pull the starchy flour down into the holes and efficiently plug them.
Also, don't run the pump for the first 10-15 minutes. Give the starches time to break down into sugar, which will be more fluid.
Unconverted starch is like paste and will clog anything. Then pulling against it with a pump will result in a stuck sparge and or collapsed bottom.

This. Although maybe not the reason for OP's stuck, it's a great tip. I always have a pump shutdown for the first 15 minutes after dough in, so the flour can convert (if mashing it at sacc temps), and let the grainbed settle naturally.

 

[seatazzz]

And +1 to the above. I let my mash sit for 15-30 minutes depending on the temperature at dough in, if higher I let it sit 15 minutes, if lower 30 minutes, before starting the pump. Timers are your friend.

 

[BudgetBrewer]

Gonna have to try this. Im usually undershooting my mash temps, so some degree of panic sets in and i fire up the pump and RIMS tube to get temps back to where they should be. Cpl deg higher strike water and a 15 min rest it is next brew day.

 

[Staticsouls]

Valve on mash tun? Was that ment to be the pump outlet? Wouldn't closing a valve before the inlet to the pump hurt the pump vs the output side?

 

[beermanpete]

2l/kg is a pretty stiff mash and it seems like there would not be much wort to recirculate after accounting for grain absorption. How much hot liquor did you add for the mash-out?

To help loosen the mash you could try underletting the mash (add hot liquor to the mash tun via the drain valve) and then stir the mash and allow to settle before resuming sparging or runnoff. Then begin the runoff slowly, less than 1l/minute to set the filter bed. A high flow rate will cause grain bed compaction and encourage a stuck sparge.

If you use a pump the valve used to control flow should be on the output of the pump to prevent cavitation in the pump. The valve on the mash tun should be fully open during this step.

The weight of the grain bed will contribute to compaction. A mash tun that is tall and narrow will be more likely to have problems with stuck sparges than a short, wide tun.