Kegging then changing temp - Has anyone experimented with this?

[CoreyG]

Hey Gang,

I've got a chest freezer I have two kegs carbed to 2.25 volumes/45 degs/12psi but I need to cold crash a fermenter before kegging it.

Has anyone ever experimented with removing the CO2 tank, letting it warm (the CO2 will likely push out of the beer, increasing the pressure in the head space). Once I am done cold crashing the other.. in lets say 4 days... putting it back in to cool. I am curious how long it would take for the beer to restabilize once re-cooled?

Also, in reverse, has anyone tried carbing warm (room temp) at 25 psi (to give you roughly 2-2.25 volumes) then cooling the beer to 40-45 degF? If so, how long did you wait for everything to stabilize?

Let me know if anyone has experience with this!
Thanks Team!

 

[Yooper]

Sure, you can adjust the psi when the temperature changes to get the same level of carbonation. I do it sometimes when my kegerator is full, or when the beer I've kegged can benefit from a bit of time at room temperature to age a bit. In my house, 30 psi at my house temperature just about equals 12 psi at my kegerator temperature, so that's what I do.

But I have no idea what you mean by this:
Has anyone ever experimented with removing the CO2 tank, letting it warm (the CO2 will likely push out of the beer, increasing the pressure in the head space). Once I am done cold crashing the other.. in lets say 4 days... putting it back in to cool. I am curious how long it would take for the beer to restabilize once re-cooled?

 

[RoundKid]

Yes, I have done both of these without issue. There is no stabilization time, you just have to wait until it gets to your target temperature.

I have two kegs at 65*F / 25 PSI right now.

 

[MagicMatt]

Yes, I have done both of these without issue. There is no stabilization time, you just have to wait until it gets to your target temperature.

There is indeed a stabilization time. Whether that matters to you is another story.

If the pressure in the headspace increases as the temperature increases, and with nothing going into or out of the keg, that tells you that CO2 is coming out of solution from the beer. When you put the keg back in the keezer, it will take ~24 hours for the temp to equalize, but the pressure will take another 5-7 days or more to fully reabsorb into the beer. If you start drinking it before this happens, your beer will be undercarbed from where you intended it. I have tested this many times - I carb my beer at 34°F and 9psi for 2 weeks to ensure it's fully carbed. I then remove it from the freezer for a few weeks. The pressure eventually levels out to about 30psi @ 70°F, which makes sense following the carb charts. However, even 4 or 5 days after putting the keg back in the keezer, even though the beer has been chilled back down to 34°F for days, the pressure in the headspace still remains close to 20psi, and will gradually and eventually fall back to the 9psi if left undisturbed for another week.

Now, back to what I said at the beginning - this may not matter to you. The amount that it is undercarbed will likely not be noticeable much, if at all. Furthermore, if you intend to leave the gas hooked up at serving pressure, the beer will become fully carbed within a couple of days anyway.

So in short, yes you can definitely get away with what you describe, but there may (or may not) be a noticeable loss of carbonation of not waiting for the release gas to fully reabsorb.

 

[doug293cz]

There is indeed a stabilization time. Whether that matters to you is another story.

If the pressure in the headspace increases as the temperature increases, and with nothing going into or out of the keg, that tells you that CO2 is coming out of solution from the beer. When you put the keg back in the keezer, it will take ~24 hours for the temp to equalize, but the pressure will take another 5-7 days or more to fully reabsorb into the beer. If you start drinking it before this happens, your beer will be undercarbed from where you intended it. I have tested this many times - I carb my beer at 34°F and 9psi for 2 weeks to ensure it's fully carbed. I then remove it from the freezer for a few weeks. The pressure eventually levels out to about 30psi @ 70°F, which makes sense following the carb charts. However, even 4 or 5 days after putting the keg back in the keezer, even though the beer has been chilled back down to 34°F for days, the pressure in the headspace still remains close to 20psi, and will gradually and eventually fall back to the 9psi if left undisturbed for another week.

Now, back to what I said at the beginning - this may not matter to you. The amount that it is undercarbed will likely not be noticeable much, if at all. Furthermore, if you intend to leave the gas hooked up at serving pressure, the beer will become fully carbed within a couple of days anyway.

So in short, yes you can definitely get away with what you describe, but there may (or may not) be a noticeable loss of carbonation of not waiting for the release gas to fully reabsorb.

With a full keg (in which the headspace volume is about 6% of the beer volume) it doesn't seem like it should take 5 - 7 days for the beer to re-equilibrate at the cooler temp. After all a keg is essentially a big bottle (bottles also have about 6% headspace), and it doesn't take a bottle that long to re-equilibrate after being put in the fridge. A bottle has a lower surface area to volume ratio than a keg, so relative reabsorption rate for a bottle should be slower than for a keg. For a half full keg, 5 - 7 days might be reasonable however. I think I'll run an experiment on this next time I fill a keg.

Brew on

 

[CoreyG]

Awesome Gang. thanks for the input. lots of things to think about.

Yooper: Sorry, i was a little bit rambly and that wasn't so clear!

MagicMatt: How did you measure the pressure you quoted for curiosity's sake, or are they more estimates? I was contemplating (mostly for fun and experimentation's sake) drilling the removable top of one of my carboys and seeing if I could hook up a pressure line and doing a few experiments.

 

[doug293cz]

Awesome Gang. thanks for the input. lots of things to think about.

Yooper: Sorry, i was a little bit rambly and that wasn't so clear!

MagicMatt: How did you measure the pressure you quoted for curiosity's sake, or are they more estimates? I was contemplating (mostly for fun and experimentation's sake) drilling the removable top of one of my carboys and seeing if I could hook up a pressure line and doing a few experiments.

The way to check what the pressure in the headspace is doing is to connect a gas QD to a pressure gauge. Then you can watch the pressure in the headspace build up as the keg sits at room temp, and then watch the pressure drop when the keg is put back in the cooler. No need to drill holes in anything.

I hope when you said "carboy" it was a typo. They should never be pressurized.

Brew on

 

[CoreyG]

Haha ya that sounds like a much better idea Doug! And yes, it was a typo... I need to do a better job rereading things better I post them!!

 

[MagicMatt]

With a full keg (in which the headspace volume is about 6% of the beer volume) it doesn't seem like it should take 5 - 7 days for the beer to re-equilibrate at the cooler temp.

I know, it was surprising to me too. I think I even posted a question about how long it should take a few years ago when I first encountered it. It makes sense that it wouldn't happen overnight, but I would think 5 days is a bit long. Though time and time again I find that is the case. Now I'm not being very scientific with my measurements (no tracking/plotting, etc), but it definitely takes more than a couple of days. I've had one in there for over a week and the pressure was still like 22psi. I finally said screw it and purged and put the CO2 on at serving pressure.

Would the liquid level being above the bottom of the gas dip tube play into this at all? I do tend to overfill my kegs at times, but I would think the pressure would read the same.

MagicMatt: How did you measure the pressure you quoted for curiosity's sake, or are they more estimates?

I use this. Got it from William's Brewing.

 

[doug293cz]

I know, it was surprising to me too. I think I even posted a question about how long it should take a few years ago when I first encountered it. It makes sense that it wouldn't happen overnight, but I would think 5 days is a bit long. Though time and time again I find that is the case. Now I'm not being very scientific with my measurements (no tracking/plotting, etc), but it definitely takes more than a couple of days. I've had one in there for over a week and the pressure was still like 22psi. I finally said screw it and purged and put the CO2 on at serving pressure.

Would the liquid level being above the bottom of the gas dip tube play into this at all? I do tend to overfill my kegs at times, but I would think the pressure would read the same.



I use this. Got it from William's Brewing.

Even if the gas tube is submerged, the pressure reading will be the same, unless you get beer into the gauge and mess it up.

If you fill above the straight walled part of the keg, then the surface area of the beer drops (very dramatically with level of over fill), which reduced the rate of CO2 absorption (absorption rate is proportional to surface area.) But, you also reduce the volume of CO2 that must be reabsorbed, so the effect offset each other.

22 psi after a week does sound flaky, since the pressure should follow an exponential decay curve.

Brew on