Cold crash suck-back volume estimate?

is there any general guidance for the volume of gas being sucked back when cold crashing?

E.g. if I have a 6.5g carboy and 5.5g of beer, and I cold crash from 68F to 35F, what volume of gas should I expect to suck-back?

if this is pretty constant and predictable, I'd like to create a large enough "gas reservoir" in my blow-off system to prevent both sanitizer and O2 from pulling back into my carboy.

FWIW, I'm thinking of just creating enough of a "gas reservoir" by lengthening my blow-off tube to provide enough volume.

 

The volume of gas will decrease proportionally to the temperature in degrees Kelvin.

68F is 293
35F is 275
With your numbers, the volume of gas will contract by about 6.1%, so you need about 0.065 gallons of reserve CO2 to prevent suckback.

If you are truly concerned about oxygen, spunding is the way to go, definitely no cold crash.

Cheers

 

We routinely see reports of a quart of sanitizer sucked into carboys. I'd make sure to cover at least that much...

Cheers!

 

Awesome. And jibes with the typical suckback horror stories wrt volumes...

Cheers!

 

Thanks. I thought I might be missing something but wasn't sure what.

 

So, I guess if I want to extend my blowoff hose to be a CO2 reservoir, I'm going to need a REALLY LONG hose...

 

Or a pretty good size mylar balloon on the far side of a catch vessel. With a bit of plumbing that should allow any liquids to end up in the catch vessel while the gases end up in the balloon...

Cheers!

 

I have observed a wild variation in the volume to satisfy the vacuum. A 6 gallon batch in a 7 gallon fermonster completely deplete a 1 gallon bladder on me twice. Other times it only deflates half way. I decided to just upgrade to 2.5 gallon bladders on my cold crash guardian product.

 

Any idea when they'll be back in stock?