Cold Crash Suckback Issue - Resolved

[IslandLizard]

I have been assuming that the crash will reduce inner keg pressure to below outside pressure. As Doug says, that cold beer will suck in a lot of co2.

Cold crashing in a closed container will indeed reduce the pressure inside. This is partly due to lower temperatures decreasing the pressure, but mostly by the beer (or water, etc.) absorbing more CO2 at lower temps until a new pressure equilibrium has been formed between dissolved gas (in the liquid) and free gas in the headspace at the prevailing temps.

I make three gallon batches in five gallon cornies. So combined headspace would be seven gallons. With a bit of a co2 bump, that there would lots of gas volume to balance out the cold shrinkage. I would be using my dispensing keg as a Cold Crash Guardian. Maybe the inner pressure would be a touch below outer pressure, but it would be much less strain on the keg than what I am doing now.

You could calculate (or just estimate) how much CO2 will be dissolved in the beer and how much will remain as gas in the entire 2-keg system.

Since you only have 3 gallons in a 5 gallon keg (having an actual volume of about 5.25 gallons), you should be able to use only the single keg, with ~12 psi of pressure in the ~2.25 gallon of headspace, keeping it from potentially imploding (or sucking air).
The 12 psi of pressure will carbonate your beer a little, so when transferring to your serving keg put a similar amount of (counter)pressure in it and slowly bleed it off while transferring (filling) to prevent excessive foaming.

 

[mac_1103]

This is partly due to lower temperatures decreasing the pressure, but mostly by the beer (or water, etc.) absorbing more CO2 at lower temps until a new pressure equilibrium has been formed between dissolved gas (in the liquid) and free gas in the headspace at the prevailing temps.

And most of us don't cold crash nearly long enough to reach equilibrium.

You could calculate (or just estimate) how much CO2 will be dissolved in the beer and how much will remain as gas in the entire 2-keg system.

Our resident beer math nerd has a spreadsheet for that but I can't seem to find the link right now.

 

[doug293cz]

And most of us don't cold crash nearly long enough to reach equilibrium.

Our resident beer math nerd has a spreadsheet for that but I can't seem to find the link right now.

You might find it down below:

Brew on

 

[Bobby_M]

A corny keg will definitely suck air in through the lid under a mild vacuum. It's made to seal under pressure but the bale handle is just there to hold the gasket in the seat so you can get the pressure started. It's not strong enough to hold the lid in place under vacuum.

 

[Bobby_M]

Yeah I still can't wrap my brain around CO2 absorption. Add a few psi and it will be absorbed so the 2 psi you put in there is still in there but somehow the pressure has dropped back to zero. Where did the pressure go? The CO2 you put in there, is in there, but the pressure is not. But for the want of a single chemistry class in HS or trade school...

I like practical analogies. Think of the headspace of a keg as the lobby at a concert venue and the beer as the actual performance space. 1000 people are lined up outside. They let all the people into the lobby all at once an hour early so they are all crammed in banging elbows constantly. They open the doors and people start filing in but it takes time because the "interface" (door) between the two rooms is small/limited..

I don't know, it sounded better in my head than it does reading it back. The pressure never actually goes to zero. It's just that proportionally the headspace is such a small amount of the total space so 2 psi will equalized down to a tenth of that or so.

 

[Climb]

Hey @doug293cz - Do you have a similar spreadsheet that incorporates volume of CO2 generated from gravity points in addition to everything else that is already in the spreadsheet you attached above? I am thinking of a scenario where a spunded fermenter is sealed before fermentation is complete.

 

[mac_1103]

I am thinking of a scenario where a spunded fermenter is sealed before fermentation is complete.

Wouldn't "End of Fermentation Pressure" account for that?

 

[Climb]

@mac_1103 Yes, I believe it would, but that is after the fact. What I am asking for is a tool that would help you determine at what gravity to seal up the fermenter based on expected FG and desired volume of CO2 or end pressure at a specific temperature. I have found the following in a post from from Kai T. from May 2010, "each gravity point gives you about 0.5 volumes of CO2". So I suppose I could run with that. Sorry, but I kind of slept through chemistry class, so anything dealing with stoichiometry, mols and Avogadro's number takes me outside my comfort zone.
Since fermentation is on going in the sealed fermenter, the amount of CO2 is more of a dynamic system. Carbonation charts don't account for new CO2 being generated. They are meant for a closed system after fermentation is complete.

 

[mac_1103]

What I am asking for is a tool that would help you determine at what gravity to seal up the fermenter based on expected FG and desired volume of CO2 or end pressure at a specific temperature.

I guess I'm still confused. Doesn't the spunding valve make calculating this superfluous? Calculate the pressure needed for the desired volumes of CO2, then set it and forget it. Are you afraid of spunding too soon? If so, why?

Carbonation charts don't account for new CO2 being generated. They are meant for a closed system after fermentation is complete.

The physics is the same. 15 PSI at 68F gives 1.7 volumes of CO2 at equilibrium whether the pressure comes from a tank or from fermentation. If you're looking for pre-equilibrium numbers, then I think the calculation is a lot more complicated.

 

[Climb]

I can understand your confusion. I was trying to hide a lot of details that most might not be interested in. Let me start by answering your questions. I believe you are thinking of a different use case that what I am. The use case I have is similar to carbonating a keg using gravity points instead of priming sugar or external CO2. I am not afraid of spunding too soon. I am not looking for pre-equilibrium numbers.
Now let me provide some background for my request and details on my fermentation system/process and my current predicament.
My fermentation system/process - My typical batch is 10.5 gallons and I ferment in a half barrel sanke. I chain the half barrel to two sixtels in serries with a blowtie spunding valve at the output of the second sixtel; i.e. at the end of the chain. I add the blowtie after the first couple days of fermentation. This allows me to purge the sixtels and spund at the same time. After fermentation, I do a closed transfer into the two purged sixtels. I have one blowtie spunding valve that has a pressure gauge that only goes up to 15 psig. I typically spund between 5 and 10 psig and finish carbonation after kegging with a CO2 tank using the set and forget method.
My current predicament - My last batch I repitched some old yeast slurry without making a starter. This is not my normal process. I was being arrogant, overconfident and lazy. So I had either an underpitch and/or very low vitality yeast; likely both. I have never taken gravity readings to verify that fermentation has ended and that the FG is close to prediction. I just let things ferment for a few extra weeks beyond normal and then keg to the sixtels. With this batch, I kegged before fermentation was complete. My FG reading happens during transfer. The FG was way high (1.021, predicted FG is 1.007) and the sample was super sweet. At this point I knew I was in trouble and decided to finish kegging anyways. So now I have slowly fermenting beer in the sealed sixtels. The gravity has dropped and has been at 1.013 (via hydrometer) for the last month. The current temp of the sixtels is about 75 F. I am trying to push fermentation to complete with this temperature. When I connect the blowtie to the sixtel the needle on the blowtie pressure gauge pegs out, so I don't know exactly what their pressure is. Anyways, this experience has convinced me that I need to start taking gravity measurements to verify that fermentation is complete. Shame on me for not making this standard operating procedure before now. And while I was reading this thread and looking at doug293cz's spreadsheet, it seemed to me that adding in calculations for CO2 generated from yet to be fermented sugars would be a nice addition to what he has already done. It would be useful for those that want to get some carbonation from gravity points instead of using priming sugar or external CO2.

 

[kohalajohn]

Cold crashing in a closed container will indeed reduce the pressure inside. This is partly due to lower temperatures decreasing the pressure, but mostly by the beer (or water, etc.) absorbing more CO2 at lower temps until a new pressure equilibrium has been formed between dissolved gas (in the liquid) and free gas in the headspace at the prevailing temps.


You could calculate (or just estimate) how much CO2 will be dissolved in the beer and how much will remain as gas in the entire 2-keg system.

Since you only have 3 gallons in a 5 gallon keg (having an actual volume of about 5.25 gallons), you should be able to use only the single keg, with ~12 psi of pressure in the ~2.25 gallon of headspace, keeping it from potentially imploding (or sucking air).
The 12 psi of pressure will carbonate your beer a little, so when transferring to your serving keg put a similar amount of (counter)pressure in it and slowly bleed it off while transferring (filling) to prevent excessive foaming.

Good. And I do closed transfer, with a gas/gas jumper, so there is no foaming issue.

 

[mac_1103]

When I connect the blowtie to the sixtel the needle on the blowtie pressure gauge pegs out, so I don't know exactly what their pressure is.

Well I guess you know it's >15 PSI at least. Can you hook it up to a regulator to measure the actual pressure? If I'm understanding correctly and you spunded from 1.021 to 1.013 then your beer may be seriously overcarbonated already.

 

[kohalajohn]

A corny keg will definitely suck air in through the lid under a mild vacuum. It's made to seal under pressure but the bale handle is just there to hold the gasket in the seat so you can get the pressure started. It's not strong enough to hold the lid in place under vacuum.

Ah. That's the answer I was looking for. I was wondering why everyone was afraid of a steel tank exploding inward from a few pounds of pressure.


But it's not that. It's that cornies need inner pressure to seal. Inner pressure is a necessary part of the corny system. The expensive fermenters with tri clamps, don't have this issue.

But that can be easily fixed. First solution, use your co2 tank to slam the headspace with high pressure gas. Not so good as it will dissolve, over carbonating your beer.
eno
Or use an external bag, using the bag Guardian thing, or a second connected keg purged with co2.

Or, as some have suggested, the headspace of a 5.25 gallon corny with only 3 gallons of beer, has enough reserve space to prevent vacuum.

Can't wait to find out if option number three will work. That would be most elegant.

 

[Broken Crow]

The expensive fermenters with tri clamps, don't have this issue.

 

[mac_1103]

Or, as some have suggested, the headspace of a 5.25 gallon corny with only 3 gallons of beer, has enough reserve space to prevent vacuum.

It doesn't. According to Doug's spreadsheet, gauge pressure goes negative even in the two kegs with three gallons of beer scenario (assuming that you start at 20C and 1 atm and crash to 0C). 5 PSI at the start of the cold crash solves that problem.

 

[Broken Crow]

...Why has no-one mentioned the BBQ regulator method yet?
https://www.homebrewtalk.com/thread...-terrible-after-kegging.725613/#post-10230872

 

[Broken Crow]

...if it helps: I often have to transfer at higher than ideal temps. I just use an expanded carb chart that goes up to room temp to know what the pressure drop will be on top of what's absorbed and set my pressure accordingly:
(I hate posting large files, but this is one that won't shrink for me and still be readable, sorry.)
EDIT: As pointed out by doug below, this chart was wrong so I removed it. Please enjoy some penguins;

 

[day_trippr]

...Why has no-one mentioned the BBQ regulator method yet?
https://www.homebrewtalk.com/thread...-terrible-after-kegging.725613/#post-10230872

My bad. Thanks for picking up the slack

 

[Broken Crow]

My bad. Thanks for picking up the slack

All's Fair in Loving Beer! You gotta be sick to death by now of folk asking about that marvellous contraption on here.... I must admit, I bookmarked it so I can build one for myself if I ever get around to commiting the space and time for a proper ferm-chamber and you and others have provided adequate instructions on how do so, so for those that can be bothered to actually read through this site can do it; Thanks! No mucking about with bags or worrying about vacuum ever!

(To everyone else; use the search function!)

 

[doug293cz]

...if it helps: I often have to transfer at higher than ideal temps. I just use an expanded carb chart that goes up to room temp to know what the pressure drop will be on top of what's absorbed and set my pressure accordingly:
(I hate posting large files, but this is one that won't shrink for me and still be readable, sorry.)
View attachment 879616

This chart has a number of problems. The worst is the temp conversions from °F to °C are wrong. The proper formula is:

°C = (°F - 32°) / 1.8, or °F = °C * 1.8 + 32°​

​

For example: 10.00°C = 50.00°F, 20.00°C = 68.00°F, 30.00°C = 86.00°F, etc.

Also, the Grams per liter used (for forced carbonation) is only correct if the beer starts with 0 volumes of carbonation. Beer almost always starts out with a significant level of carbonation at the end of fermentation. Beer fermented at atmospheric pressure (0 psi gauge) and 50°F will have 1.14 volumes of carbonation, fermented at 60°F will have 0.96 volumes, and fermented at 70°F will have 0.81 volumes. Let's say your beer starts out with 0.9 volumes of carbonation, and you want 2.5 volumes. In this case you need to add 1.6 volumes of additional carbonation. 1 volume of carbonation is equal to 1.977 g/L of dissolved CO2, but for simplicity we'll just round that to 2 g/L as that's what the chart uses. That means you use 1.6 volumes * 2.0 g/L-volume = 3.2 g/L of bottled CO2 to finish force carbing, not the 5.0 g/L as given by the chart.

The carb levels in the chart also don't match up with the results of the "best" carbonation formula of which i am aware - equation 2.1 in the attached .pdf.

Brew on

 

[Dave C01]

The water sucked back from the airlock bucket into the accum chamber falls to the bottom of the accum chamber, and CO2 from the fermentation process is "returned" to the fermentation vessel.

That water will contain some dissolved oxygen. Some of that dissolved will inevitably be liberated from the water and mix with the CO2. Not a lot, but worth considering!

 

[Brockness Monster]

Beer fermented at atmospheric pressure (0 psi gauge) and 50°F will have 1.14 volumes of carbonation, fermented at 60°F will have 0.96 volumes, and fermented at 70°F will have 0.81 volumes. Let's say your beer starts out with 0.9 volumes of carbonation, and you want 2.5 volumes. In this case you need to add 1.6 volumes of additional carbonation.

If vigorous fermentation starts out at 70F, but drops to 60F near the end with slow fermentation continuing for a day or two, do we calculate based on 60F or 70F?

 

[mac_1103]

If it's been at 60F long enough for the beer to reach equilibrium with the head space, then you should use 60F. A day or two is probably not long enough to reach equilibrium.

 

[kohalajohn]

View attachment 879615

Well, I dont think that was in the recipe.

 

[beren]

My bad. Thanks for picking up the slack

That’s an amazing idea I love it.

 

[kohalajohn]

It doesn't. According to Doug's spreadsheet, gauge pressure goes negative even in the two kegs with three gallons of beer scenario (assuming that you start at 20C and 1 atm and crash to 0C). 5 PSI at the start of the cold crash solves that problem.

But I ferment under pressure, at 12psi.

But I'm not a math spreadsheet guy. I'll have to find out in a few days from now.

 

[mac_1103]

I'm not a math spreadsheet guy

Doug did all the work. All you have to do is plug in your numbers. And since I mentioned that 5 PSI solves the problem, it stands to reason that 12 PSI would too.

 

[doug293cz]

If vigorous fermentation starts out at 70F, but drops to 60F near the end with slow fermentation continuing for a day or two, do we calculate based on 60F or 70F?

Would depend on how many gravity points got fermented at the lower temperature, which determines how much CO2 will have been generated. Also, need to know the volumes of beer and headspace to determine if the generated CO2 was enough to saturate both. Not a simple calculation to do. If you are bottling, then you might want to avoid a situation that leaves an indeterminate level of carbonation in the beer, in order to minimize the chances of over or under carbonating.

Brew on

 

[doug293cz]

If it's been at 60F long enough for the beer to reach equilibrium with the head space, then you should use 60F. A day or two is probably not long enough to reach equilibrium.

If there is active fermentation at the lower temperature, then the carbonation level will increase much faster than if CO2 was just being absorbed from the headspace.

Brew on

 

[Snuffy]

View attachment 879615

Is that the fermenter from the Titan sub?