Crash Cooling - Airlock or Stopper? How to prevent suck in?

When crash cooling a carboy, I assume that the negative pressure would result in drawing in liquid in the airlock and outside air.

So do people use a stopper? Since the temp is dropping so much, would there not be the risk of the stopper getting sucked into the carboy?

I've searched through a few cold crashing threads and I don't see this addressed. What technique do people use?

matts said:

When crash cooling a carboy, I assume that the negative pressure would result in drawing in liquid in the airlock and outside air.

So do people use a stopper? Since the temp is dropping so much, would there not be the risk of the stopper getting sucked into the carboy?

I've searched through a few cold crashing threads and I don't see this addressed. What technique do people use?

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I use a double bubble style airlock filled to just below the fill line so I usually don't have to worry about suck back.

I remove the airlock before I crash cool and cover with plastic wrap and a rubber band. A stopper would also work. The first time I crash cooled I sucked up a full pint of star san through the blowoff. It ended up fine though.

rack04 said:

I use a double bubble style airlock filled to just below the fill line so I usually don't have to worry about suck back.

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Thanks, I don't use those but was wondering how they handle suck back. But, even though you aren't sucking in liquid, aren't you still sucking in outside air? Contamination probably isn't very likely from that, but what about oxidization?

JonK331 said:

I remove the airlock before I crash cool and cover with plastic wrap and a rubber band. A stopper would also work. The first time I crash cooled I sucked up a full pint of star san through the blowoff. It ended up fine though.

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Sounds like a good idea, how much does the plastic wrap get sucked down?

RDWHAHB is what SWMBO always tells me.

Seriously, a double bubbler is probably the simplest semi-safe solution. You are going to be sucking in air, but its not so much that its going to cause you any major oxidation problems.

If your paranoid, rig up a sealed plastic bag filled with C02 and insert your blowoff tube into that. Or use an extra long blowoff tube with the end submerged in vodka, that way all of the air that gets sucked back up is actually CO2 that the yeast was blowing off prior to cooling. And if it sucks up too much, hey you have a higher alcohol beer!

I have always used bubbler type airlocks filled with starsan and have never ever had a problem.

matts said:

Sounds like a good idea, how much does the plastic wrap get sucked down?

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Not a huge amount of pressure so not much. The small amount of liquid in an airlock getting sucked in doesn't really bother me that much. The problem is that once the liquid gets sucked in, there is not much of a barrier between the beer and ambient air. If I'm in a really paranoid kinda mood, I soak a paper towel in star san, wring it out, and then put in on the carboy first and then the plastic on top. this way, if any air is sucked in around the rubber band, at least it has to pass the sanitizer soaked paper towel first. Overkill but....

I haven't tried it, but you could possibly use one of those foam stoppers for yeast starters. Let it soak in star san, wring it mostly out, and then wedge it into the neck of the carboy. What do you think?

I didnt see (notice) OP was using a carboy. In that case I second the idea to just soak a bunch of folded over paper towels in Starsan, and wrap a gum-band (yea thats what we call em here) around the top. No need to get elaborate (unless your paranoid and wear aluminum foil caps on your head while brewing).

https://www.homebrewtalk.com/f163/temp-reduction-suckback-lets-brainstorm-152658/


What I have done is to make a bag using my Food Saver. I cut an 18 inch length from an 11 inch wide Food Saver roll and sealed one end. Then I made a small hole in one corner of the sealed end and inserted the end of a 1/4 inch vinyl tube, securing it with DAP Household Adhesive Sealant (100% Silicone) from Lowe's. After the adhesive cured, I sealed up the other end of the bag. I put a barb-to-barb adapter on the end of the tube to connect it to my CO2 supply, with a clamp on the tube, near the barb adapter. I turned the CO2 pressure down very low (I think maybe only 1 or 2 PSI), connected the bag to the CO2, and began to fill the bag slowly. When the bag was nearly full (don't fill it too full, or it may pop; also you don't want the bag to be pressurized, just full) I closed the clamp on the tube. Now you can put the bag onto your carboy cap or bung (you will have to figure out what kind of adapter to use on the end of the tube, depending on how you want to connect to your cap or bung) and release the clamp.