Suck Back Mystery

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Active Member
May 28, 2016
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This one has me puzzled.

I ferment in a Brew Bucket and use the blowoff hose. My latest batch is a RIS. I put it in the fermenter, with some fermcap (I've got a lot of experience with excessive blowoff with big beers), blowoff tube in a 1 gal pitcher (with about 1.5" of starsan solution in the bottom) placed on the bottom of the ferm chamber. All in the fermentation chamber at about 60 deg.

Primary fermentation goes as expected. Everything finishes up. I open the door and let it rise to basement temperature of a pretty constant (for this time of year) 72 deg. All is good.

Being a RIS, I'm giving it 3 weeks in the primary before racking to the secondary for bulk conditioning. I check the blowoff pitcher every day to make sure it doesn't go dry (although it really doesn't matter, I suppose.) One day I notice the pitcher is empty and there is some liquid still trapped in the tube?! I pull the tube from the fermenter to empty it, and add some more liquid to the pitcher. A few day later it happens again.

I installed an airlock, but I can't figure out what would push the liquid up over 20".

No temperature changes, no samples pulled from the valve that would cause a drop in pressure in the vessel, no leaks. I'm stumped. Thoughts?


Well-Known Member
Jun 27, 2011
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El Dorado Hills
I'd say the temperature dropped and a siphon was created.
(I know you say you didn't change the temp)