Keg Pressure and Cold Crashing

[TAK]

If you put some pressure on a keg and REMOVE the gas in line, then cold crash (or slowly cool), even though some CO2 will go into solution, there's no way that you'll loose enough pressure to keep a good seal on the keg, is there?

For example, I put 16 PSI on my keg today, and now I'm slowly cooling into lager temps. I'm not connected to the tank to maintain that PSI. So as it goes into solution, I expect the keg pressure will drop. But, it's not going to drop enough that I need to worry about the seal on my lid, do I?

And related, say I were to have gone to 30 PSI and removed the gas in line. That 30 PSI in the headspace with, say 4.5 gallons of beer in a 5 gallon keg, that's still not enough to carb the beer is it? I doubt that it would be, and my question isn't because I would want it to be, rather, I didn't put much PSI on the keg because I wasn't sure if I could possibly put too much carb by doing this and cold crashing.

It's not like I'm really concerned about either of these prospects, just thought I'd ask to get some feedback.

Cheers

 

[thadius856]

Certainly you'll drop into single digit pressures.

You have one headspace of 16psi. Lets call it 1 gallon of headspace for simplicity (probably more than you have in your corny). 16 psi will turn into 2.67 psi (1/6th) after that CO2 dissolves into the beer. It'll take some time to drop that low, but it will.

The math's a little crude, but it illustrates a point.

I don't trust my kegs below 5 PSI, personally.

 

[TAK]

Certainly you'll drop into single digit pressures.

You have one headspace of 16psi. Lets call it 1 gallon of headspace for simplicity (probably more than you have in your corny). 16 psi will turn into 2.67 psi (1/6th) after that CO2 dissolves into the beer. It'll take some time to drop that low, but it will.

The math's a little crude, but it illustrates a point.

I don't trust my kegs below 5 PSI, personally.

So, I should periodically push a bit more PSI into it then, huh?

 

[thadius856]

Might as well carb it, either naturally or by force.

Beer still ages while carbed.

 

[TAK]

Might as well carb it, either naturally or by force.

Beer still ages while carbed.

This keg will get carbed soon while it's lagering, it's just cooling down in my fermentation fridge while it's waiting for a spot in my kegorator. Once it has a spot in the kegorator, I'll have the CO2 hooked up. But right now it's standing alone.

 

[TAK]

I've still got some questions about this topic. I'd like to start cold crashing (in a keg) to get the yeast settled out before dry hopping my IPAs. I don't really want the beer to be carbed when I dry hop it though. I would cold crash for a few days, then bring it back up to cellar temps for the dry hopping.

During the cold crash, of course you need enough pressure on the keg, or already in the keg, for it to hold it's seal. However, I don't want it to carb up yet. I know lots of others do the same thing, but I've never seen any mention of the pressure used to keep a cold crashing keg sealed but not carbed. Do you put X-amount of PSI on it then remove the gas-in, or do you keep the gas-in on it and only hold X-PSI for the crashing period?

I know some of this will probably become apparent after a few batches of experience, but I'm hoping to leverage the experience of others here at HBT to get it done right the first time.

Cheers.

 

[thadius856]

Why do you need to cold crash in a keg?

Cold crash the primary. The longer, the better. With a 4 week primary and a 3 day cold crash, you're not going to get much improvement out of a secondary with another cold crash. If you're really upset about the slightest haze, I think you might want to look into filtration systems.

But to answer your question anyway...

To seal a keg without carbing the beer, just hit it with ~30psi and remove the gas supply. Assuming it's fairly full of beer, the headspace CO2 is negligible. Remember, the beer already contains residual CO2 from fermentation anyway. The CO2 will reach equilibrium with the beer eventually, so you'll have to boost it every week or two to maintain pressure.

I think the reason you're asking this question is because you're confusing dryhopping carbed beer with dryhopping in primary. It's perfectly fine to dryhop carbed beer. Dryhopping in primary will have the yeast's CO2 production push a lot of the aromatics out the airlock.

I have several kegs on tap right now that are carbed and still have the dryhop hanging in the keg. And they're absolutely delicious.

 

[TAK]

Thanks for the tip, 30 PSI in the headspace and let it equalize.

To get more specific, the reason I’m interested in cold crashing in a keg is multifaceted. However, it’s not a matter of confusion. The primary reason I’m interested in cold crashing at all is to get the yeast to drop out of solution as a benefit to the dry hopping step. I’m not really concerned about haze. Some of the hop oils bond with the yeast, so if you dry hop while they’re still in solution, when they do crash, they pull some oils with them. With this said, I do understand that there are benefits of dry hopping other various ways, such as in primary after fermentation, in the primary with a few percent attenuation left, in any vessel at various temperatures, and/or in the serving keg. They’re all worth experimenting with; I’m just thinking logistics around one specific method here: dropping the yeast, dry hopping, and then serving.

I do like the idea of dry hopping in the serving keg, but I’m not really sure about using the same charge of hops that I let the beer sit on at room temp for however many days. I’m sensitive to the vegetal flavors that come with prolonged exposure to dry hops. So, if I’m dry hopping a carbed beer that’s on tap, it’s with a fresh charge of hops and suspended 1/3rd the way down the keg. This way it’s left above the surface of the beer after a couple weeks of drinking.

The reason I want to do the cold crash in a keg instead of the primary is to get it done quick with the least amount of problems. I know lots of people cold crash in the primary and find in their experiences there are no issues. In my take, I have a couple concerns that are enough to lead me to avoid this method. If you cold crash quickly, this can stress the yeast and they’ll release excess esters/phenols. More of my concern is that as the liquid cools it contracts. So, at a minimum, you have to take the airlock off the primary. Still though, unless you’re setting up a work-around, the beer is pulling in regular old unfiltered air, and likely some O2 is going into solution. Neither of these may be a big concern, but cold crashing in the keg is an easy solution to both.

The reason I don’t want to carb in the cold crash keg is because the hops will then cause nucleation sites when introduced, or agitation when removed, causing foam. Moreover, I’ll probably be cold crashing in one keg, bringing the temp up and dry hopping in the same keg, then transferring off the dry hops into a second keg, and again, a carbed beer will foam during the transfer. In general, foam is built from one-use-only proteins, so I want to do the best in every step downstream not to foam the beer.

 

[thadius856]

While these are all theoretically valid concerns, I've never seen them manifest themselves in the real world.

My beer doesn't taste oxidized, it don't encounter foaming issues, and head retention is fine.

To each their own. That's what makes this hobby so great.

 

[TAK]

Absolutely, and cheers to that. I am a self ascribed over-thinker for sure. All of this business about cold crashing is because I haven't really done it before, so I think a ton going into it for the first time.

I have had head retentions issues, for example, so I'm attacking every angle to solve that going forward.

Since you cold crash in the primary, do you mind expanding on the details? Do you remove the airlock and cover with foil or something like that? Do you step it down to the 30's or move from the fermentation temp to that temp as quickly as possible?

 

[thadius856]

Sure.

Temperature control is via a freezer-based ferm chamber (7 cu ft GE with 16" collar). It holds two Vittles Vault 80# units, each with a capacity of 20 gallons. Since the hump is 9.25" tall, they sit atop a 2x10 frame a layer of plywood to give a perfectly flat, supportive surface.

Primary is typically 57-60F (liquid temp, not ambient), but varies based on yeast and recipe. I've recently switched to 4 weeks primary, with the cold crash taking up the last 3 days of it.

I set the controller down 10F and put a box fan in front of the freezer to help ease the compressor in heat exchange. I have an oversized recirc fan that helps keep the air moving. 10F typically takes 3-4 hours, and I get the compressor a 1 hour rest before cranking down another 10F. On the last temp drop, I set the controller to cycle between 34-37F, then leave it until the 3 days is up.

Without moving the primary, I unscrew the lid and attach a cask widge, which skims the top layer of liquid. I siphon directly into the serving keg, then throw the first 5 gallon keg into the keezer and carb at 3x serving pressure (as determined by a vol CO2 calculation for the style) for 24 hours. The rest go into a 70F closet for bulk aging until they're needed for serving.

If there's dry hopping involved, none go in the keezer immediately. Dry hops are suspended from a paint strainer bag with dental floss for the time prescribed in the recipe.

Because the primary was completely undisturbed for the entire 4 weeks, the beer comes out pretty freakin' clear. All remaining yeast and sediment serve off in the first pint or two.

Edit: I don't use airlocks. I use 4' of 5/16" ID blowoff tube, with the end in about 6" of StarSan inside a 16oz Gatorade bottle with a drilled lid. I've never had StarSan suck back into the fermenter, perhaps because there's about a 2.5' elevation it would have to climb to enter the fermenter.

 

[Yesfan]

The last two batches I cold crashed, I just put the primary in the keezer and took it out and transferred after a couple of days. I also let the kegs sit on about 20-30 psi for a day or two, then drop the pressure to around 12psi and the kegs sit on that for two weeks before I start serving.

It might not be the right way (or preferred way), but that's how I have done it. Like Thadius mentioned, "to each their own" but I am always open for suggestions on how to do something easier that's just as productive.

 

[day_trippr]

I'm actually near the end of cold-crashing two batches in their primary/only fermenters (6.5g carboys). I dry hopped both with free-swimming pellets on Monday morning, switched out the blow-offs for s-locks, turned the fridge controller down to 50°F yesterday evening, turned it down to 35°F just before I went to bed around midnite, and they reached 35°F this morning.

The hops are slammed to the bottom and there's a two inch bright band on the top of both carboys as the last yeasty/trubby bits drop. I could wait a few/many days for that line to continue to drop, but as I'll be "slow force carbing" these for at least two weeks I'll rack above the dregs while doing a CO2 push, keg these tomorrow, and let them brighten while they carb in a separate cold-conditioning/carbing fridge on their eventual way to the keezer.

I stopped using secondary vessels even when dry hopping (which is pretty much part of every batch I do) two years ago after trying this process out and realizing I could cut out an entire transfer (with everything that entails, pre-sanitation, post-cleaning, and oxygenation-avoidance -wise) and end up with equal if not better quality product.

As for oxygenation during cold-crashing, no doubt there's some amount of that, but the only cold-crashed batch in which I've ever detected oxygenation effects was due to kegging with a suddenly recalcitrant auto-siphon (that was promptly dispatched to Polycarbonate Heaven with the switch to CO2-push).

Considering the potential CO2 displacement due to headspace pressure drop along with the short exposure during the crash, I choose to assume any deleterious effects are minute in magnitude...

Cheers!