Mash floated while sparging???

[ChzyMnky]

Hi all,

I brewed this past weekend, and had a really weird problem that I've never encountered. I have a 15gal kettle tun with a RIMs tube and chugger pump. This recipe has a really long mash/recirc (~3 hours including step time), and it had all gone normally. The grain bed was nice and settled with only a few bits of grain floating at the top of the kettle. I stepped the mash up to 168 for mash-out, and after the grain bed had reached temperature I stopped the pump to attach my sparge arm. While I was doing that, bubbles started coming up through the grain bed, and then the entire grain bed (I think, it was hard to see) slowly floated up to the top! I didn't know what to do, so I just sparged right on to the grain and got some really terrible efficiency. (My pre-boil gravity was supposed to be ~1.070, but was only ~1.055). This is only about my fourth brew on this kettle/false bottom, so I'm still dialing in my process. Anybody have any ideas on what happened, and a way to prevent it in the future?

Here's some details:

Equipment
15 Gal kettle with false bottom & recirc port
RIMs
Chugger pump

Mash
21lbs of assorted grains
~0.5lbs of rice hulls
~5oz crushed pecans
Mashed at ~1.9qt/lb

Temp Steps
Step 1: 30min @ 122
Step 2: 120min @ 144
Mash Out: 10min @ 168

Thanks in advance for the help!

 

[Smellyglove]

You're recirculated just a bit to hard. It has happened to me lots of times. The mash looks great during recirc, but when you stop the pump bubbles emerge from the depths bringing grain with them.

 

[day_trippr]

Where do the bubbles come from?
I've never experienced anything like that, and my expectation is there should never be bubbles in a fully doughed-in mash...

Cheers!

 

[ChzyMnky]

SmellyGlove, thanks for the info.

day_trippr, I have the same question...

I wondering, would it be beneficial to pause the pump for a minute or two in the middle of the mash? If there is trapped air under the grain bed, it would give it time to escape and then reset the grain bed before the sparge... What do you think?

 

[Gnomebrewer]

Given the poor efficiency and air pocket, you may have had a dough ball - a ball of unmixed grain.