Cold Crashing Under Pressure

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kmind

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Total noob with fermenting under pressure/trying to avoid the oxygen suck back issue of cold crashing. Bare with me and you may have to explain it like I'm 5.

I'll be using a Fermzilla All Rounder to ferment under pressure for my first time. I've read a few different answers on cold crashing and just want to make sure I understand everything correctly. Assume I will be fermenting under 15psi, and I don't want to carbonate the beer much at all during the cold crash.

1. Can I simply just take off the spunding valve and set the temperature to 34 degrees? The lid has a gas and liquid post so I would assume no oxygen would get sucked in unless I had a leak?
2. Can I actually leave the spunding valve on or can oxygen still get sucked in through a spunding valve?
3. If questions 1 and 2 wouldn't work, should I just hook up CO2 from my tank and keep it at about 2psi during the cold crash?

Thanks so much!
 

burtom

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Take off the spunding valve and crash away. You should drop About 5 PSI going from 68 to 32 degrees.
 

DuncB

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you could start your cold crash with more pressure that way the carbing is occuring during the crash. So you will be able to drink the beer sooner.
 

apache_brew

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Your spunding valve won't let air in unless it incorporates some sort of vacuum relief (most dont). It's a one way valve that relieves pressure at the point you set it to. If you have a pressure gauge integral to the spunding valve, i'd just leave it on so that you can see for yourself how much the internal pressure reduces due to crashing. Like @burtom said, it will be around 5 psi drop. As long as you have positive internal pressure, you don't have to worry about oxygen getting in. Spraying starsan on all you connections under pressure is good indicator for leaks if you have any.

Hooking up a CO2 line would work too, just make sure you have a check valve on the line do you don't risk back pressurizing your co2 line/regulator.
 

ajm163

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Why would you need to take the spunding valve off?
 
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kmind

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Why would you need to take the spunding valve off?
No reason, I just wasn't sure if a spunding valve was a one way valve really. I would have only taken it off if I knew it could suck back oxygen.
 
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kmind

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Thanks for the replies!

I think I'll keep the spunding valve on to monitor how much pressure I lose. But it's good to know I can either keep it on or take it off. Just wasn't too sure.
 

Jim R

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Are you planning to just drink it from the Fermzilla? Do you keg?

With my Fermzilla All Rounder, I do a pressure transfer to my keg after fermentation is complete through the floating dip tube. Then I cold crash in the sealed keg and maintain the correct pressure to complete carbonation. The advantage of this is that I am keeping most of the trub and debris out of the keg before I cold crash. Plus the keg takes less space in the refrigerator than the All Rounder. Of course, it also frees up the All Rounder for another batch when I am ready.
 
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kmind

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Are you planning to just drink it from the Fermzilla? Do you keg?

With my Fermzilla All Rounder, I do a pressure transfer to my keg after fermentation is complete through the floating dip tube. Then I cold crash in the sealed keg and maintain the correct pressure to complete carbonation. The advantage of this is that I am keeping most of the trub and debris out of the keg before I cold crash. Plus the keg takes less space in the refrigerator than the All Rounder. Of course, it also frees up the All Rounder for another batch when I am ready.
I keg so I was planning on transferring after cold crashing in the All Rounder. You make some interesting points that I may have to test out at some point.

Could you go into more detail on how you cold crash and carbonate? What kind of PSI do you typically cold crash at to get the correct carbonation? Do you use a spunding valve when cold crashing? Thanks!
 

doug293cz

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The All Rounder has a listed total volume of 7.9 gal. If you have 6 gal of wort, then you have 1.9 gal of headspace. If you spund at 15 psig, at the end of fermentation the headspace will contain 100% CO2 at a partial pressure of 29.695 psi (spund pressure + atmospheric pressure.) If you fermented at 68°F (20°C) and then cold crash instantly to 32°F (0°C) then the headspace pressure will drop by ~2 psi just from the temperature contraction of the headspace CO2. The calculation looks like this:

New absolute pressure = 29.695 psi * 273.15°K / 293.15°K = 27.67 psi​
The beer will have 1.7 volumes of carb after spunding @ 15 psig and 68°F (0°C). The cold crashed beer will absorb CO2 from the headspace over time. If the vessel is sealed, the headspace pressure will drop as the cold beer absorbs CO2. When equilibrium is reached, the new headspace pressure will be 3.0 psig (17.7 psia), and the carb level will have increased to 1.9 volumes.

The good news is that the gauge pressure never goes negative (partial vacuum) if you do a sealed cold crash. I tested scenarios up to 7.5 gal of starting wort, and the final pressure still didn't go negative.

Brew on :mug:

Edit: corrected typo "2.9" -> "1.9"
 
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Jim R

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I don't really ferment under pressure to achieve "correct carbonation." I do it mostly just because I can with the Fermzilla. It also probably speeds up fermentation a little at a slightly higher temperature. Probably the biggest benefit is that is greatly reduces the risk of oxidation.

I usually set my spunding valve to 12 psi or so for fermentation. If I have en empty keg I fill it with sanitizer and purge it with the fermentation CO2 by connecting a hose from the spunding valve to the gas port on the keg. When fermentation is done, I then do a pressure transfer to the purged keg and cold crash the keg without the spunding valve. I then apply the correct pressure to the keg (usually 12 psi or so) and let it carbonate as I let it age for a week or so before tapping the keg. The carbonation level right out of the fermenter doesn't really matter to me.
 
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kmind

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Thank you all very much!
@doug293cz - I'll probably have to reread your post a few times for my brain to grasp everything but awesome stuff!
 

renstyle

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The calculation looks like this:

New absolute pressure = 29.695 psi * 273.15°K / 293.15°K = 27.67 psi​
I wish you were my math teacher in college... or my chemistry teacher LOL Just earlier tonight, I was having a boyle's law brain block... The explaining part, you're really good at it. :D
 

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