[Brian]

I use a .5 inch hose coming out of the top of my Ss Brewtech Brew Bucket. It runs into a sanitized growler filled about 3/4 of the way up with starsan.

A couple months ago I noticed one batch had sucked about half the sani fluid into the fermenter. I talked it over with my brew club and we hypothesized it had to do with a temperature change.

Fast forward to today and I just noticed the ENTIRE volume of sani fluid has been sucked into the fermenter this time. Has anyone had this issue? Any ideas how to fix it?

[MattyAHA]

if temps drop rapidly it creates a vacuum and sucks airlock liquid back into the fermenter, another possibility is the airlock dried out, i have had that happen to me before both scenarios

[denny]

What I do with my conical is seal it and add CO2 pressure before crashing.  Can you do something like that?

[Village Taphouse]

I've seen the vacuum gig myself.  It's rare but it happens.  I have a line running from airlock-to-keg-to-blowoff-bucket and sometimes the sanitizer in the bucket ends up in the keg.  Freaks me out every time. 

[MattyAHA]

i just lower temps slow, if its not a sealed up system it will happen if you crash too rapidly, i dont care about getting star san in my beer as much as i do getting air in, the air is more harmful then the star san, in a perfect situation you should get neither in, so either crash slowly or like denny said crash in a sealed vessel(conical,keg etc etc)

[allenhuerta]

Like everyone else, I'm assuming your cold crashing but could you tell us where in the process this is? Or is it just in an area and that changes a lot?

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[KellerBrauer]

Also, where is the growler located in relation to the conical?  If it’s higher, than I’m wondering if temperature draws star-san back just enough to start a siphon. After that, game over.

[Brian]

Thanks for the replies everyone.

This isn't happening during cold crashing. It happens at a random time during fermentation. I did realize while reading people's comments that my AC is set to drop 2 degrees in the evening. I have been watching the temps closely and I think the temp drops probably 2 to 5 degrees overnight. Maybe that's enough to create a vaccuum. Sounds like it's time to invest in some jackets for my brew buckets!

[jrobe]

I got burned with this once while cooling down my SS Brewbucket late in fermentation.  I haven't heard of this before though without lowering the temperature by more than just a few degrees.  Look up "cold crash suck back" and you will see lots of information and many different possible solutions including balloons to capture CO2 and this solution.

https://www.homebrewersassociation.org/forum/index.php?topic=30363.0

I eliminated this myself when I started using a temperature controlled fermentation chamber with a mini refrigerator that holds the SS Brewbucket and an Inkbird temperature controller to maintain a stable fermentation temperature.  Then I transfer the beer to my kegs before I cool it down to serving temperatures.

[MattyAHA]

Thanks for the replies everyone.

This isn't happening during cold crashing. It happens at a random time during fermentation. I did realize while reading people's comments that my AC is set to drop 2 degrees in the evening. I have been watching the temps closely and I think the temp drops probably 2 to 5 degrees overnight. Maybe that's enough to create a vaccuum. Sounds like it's time to invest in some jackets for my brew buckets!

it can happen anytime the temp drops too rapidly, it can be during primary,secondary,crashing anytime the temp drops and you are not in a sealed vessel