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Old 04-01-2013, 02:47 PM   #1
Feb 2013
Posts: 117
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So I am cold crashing for the first time , and the airlock is moving in reverse sucking air back into the carboy. I understand the physics of it but don't like it. It is obviously sucking air with O2 back into my carboy. I suppose since CO2 is heavier than air, there will still be a blanket of CO2 over the beer to stop oxidation but it feels wrong. Any opinion/experience out there. Should I have done something else?

Thanks, t

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Old 04-01-2013, 03:55 PM   #2
Apr 2012
Schenectady, New York
Posts: 916
Liked 116 Times on 93 Posts

How much air depends on the amount of headspace.

Air on average will lose about 4cc of volume per liter for each 1 degree drop in temperature.

If you have 1 liter of headspace in your carboy and reduce the temperature from 65 to 35 you will be sucking in about 120cc (4ounces). As to the effect this will have I do not know.

Less headspace means less suck back.

Hope this helps??


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Old 04-01-2013, 07:34 PM   #3
May 2011
Stow, MA
Posts: 18,949
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I think the whole "blanket" thing is a myth, and the air will diffuse into the CO2/vice versa, which supports the notion of keeping a minimal headspace.


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Old 04-01-2013, 07:40 PM   #4
terrapinj's Avatar
Dec 2010
Santa Monica, CA
Posts: 2,415
Liked 170 Times on 126 Posts

i started using a solid bung to plug the lid in my bucket when I cold crash

i left the airlock on for many batches though and never noticed any oxidation etc, 5.25gal batch in a 6.5gal bucket

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