[morticaixavier]

I'd be careful about cold crashing in a closed vessel. I've read stories of pro brewers having conditioning tanks collapse in on themselves from sealing it during cold crash. If a steel tank can collapse in on itself I have even less faith that a BB isn't going to suffer the same fate.

there are scale issues to contend with volume to surface area on a 15 bbl fermenter is very different than in a 5 gallon better bottle. You are only dealing with a few percentage points of shrinkage, which on a small scale isn't that big a deal.

[S. cerevisiae]

You do not have to worry about oxidation during cold crashing because yeast cells will be in suspension long after the beer temperature equalizes with the ambient temperature.  At that point, you can fill the airlock. Oxidation only becomes a serious threat after beer has been filtered.

[S. cerevisiae]

I do not cold crash.  I just rack to a secondary after 10 to 14 days in the primary and wait for the beer to fall bright if I want non-yeasty beer on the first pint.  Cold crashing a primary for a few days does not fix the protein and hop compound precipitation problem.

[dougsoulang]

Thanks for all of the input. Much appreciated.

[Steve L]

I wonder at what point suck back becomes an issue? Is this only when you cold crash as opposed to slowly lowering temps or is there a low temp threshold at which this occurs? Or is it a steady gradient of suckage that increases as the temps drop? I have lagered before at around 40F with a bung and airlock in place but I don't know that I've ever experienced suck back? Just curious.

[morticaixavier]

I wonder at what point suck back becomes an issue? Is this only when you cold crash as opposed to slowly lowering temps or is there a low temp threshold at which this occurs? Or is it a steady gradient of suckage that increases as the temps drop? I have lagered before at around 40F with a bung and airlock in place but I don't know that I've ever experienced suck back? Just curious.

If the vessel is sealed except for the air lock the pressure inside will drop as the liquid cools and contracts until it hits 0°c and the liquid stops contracting.

[Steve L]

Does the Suck back phenomenon introduce enough air into the fermenter as to cause oxidation? I would be more worried about that than getting airlock liquid into the fermenter. One could simply use an "S" type that bubbles both ways.

[dougsoulang]

Just a quick update for those that might have been curious. I cold crashed at 34F for two days, and there was a bit of flex due to the volume change in the Better Bottle. But nothing that made me fear that there would be permanent damage to the Better Bottle itself.