Carbonating in keg, high psi but low carbonation

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beervoid

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Hello everyone, I'm trying to understand something and maybe the science wizards over here can help.

I spund my kegs which I ferment in at the end of fermentation to approx. 5psi for some residual natural carbonation.
Before cold crashing I pressurize the keg to 30psi and disconnect the gas. I then continue to crash to 1c.
The next day the pressure will have dropped to about 20psi for bigger beers and 12-15psi for smaller beers. (I'm guessing this is cause bigger beers are thicker so carbonation takes longer)

After the crash to 1c in approx. 24h I continue and transfer to the serving keg. I pressurize it to 30psi and disconnect the gas.
Now here is where it becomes strange for me.
I check the keg pressure every day to see how much co2 has absorbed into the beer and I can see the pressure going down. This goes very slowly though.
I'm now about 10 days in the pressure on the keg is a stable 22psi since the last few days. (the keg is almost filled to the brim)
If I sample the beer there is not much carbonation.
The kegs are stored at 2c, so if the pressure doesnt drop anymore I would expect the kegs to be overcarbonated (aim is 2.3 volumes so around 12psi at this temp)
Can someone explain to me what might be going on?

Is the carbonation just going very very slow?
Does headspace in the keg matter for the speed of co2 absorption?

Thanks alot!
 

CascadesBrewer

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I am not quite sure about what you are seeing with "the pressure on the keg is a stable 22psi", but if you want to force carbonate your beers, you need to keep the CO2 connected. Unless you have a LOT of headspace in your keg, there is not nearly enough CO2 just in a pressurized headspace to carbonate the beer.
 
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beervoid

beervoid

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I am not quite sure about what you are seeing with "the pressure on the keg is a stable 22psi", but if you want to force carbonate your beers, you need to keep the CO2 connected. Unless you have a LOT of headspace in your keg, there is not nearly enough CO2 just in a pressurized headspace to carbonate the beer.
Ok, so for this particular keg that is filled to the brim, wouldnt the little co2 thats in that small headspace be absorbed very fast then as its only a little bit?
 
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beervoid

beervoid

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It would but you need more than that to get the amount of co2 dissolved in the beer to an acceptable level.
But why is the pressure not dropping?
I just connected another keg, this one has been sitting on 22psi for another 5 days without changing.
Connected it to my kegerator and it has hardly any carbonation.
 
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beervoid

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Could it be that since they are filled more full there is little surface area to carbonate so it goes super slow?
 

ScrewyBrewer

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Some time ago I read that corny kegs should only be filled up to the top seam, where the domed head joins the straight sides of the keg. Which measures 2 7/16 inches on my ball lock kegs.
corny-keg-1.JPG
 

DuncB

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That fill level advice might be to reduce the chance of beer going back up the gas post, I have non return gas ball locks and short gas posts on my kegs.
 

ba-brewer

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I cant really help but I do know the surface area the CO2 is exposed to determines how fast the CO2 is absorbed into the beer. That is why laying a keg sideways or shaking it makes it carb faster because the surface area is increased.

If the keg is very full and the surface area of the beer is small it should take longer to get it carbonated.
 

Spikybits

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I typically leave the gas CONNECTED at 30PSI at 34F for 2-3 days depending on the carb level desired.

I do cold crash in a mini fridge and pressurize the keg to 30psi, then disconnect. the beer in the minifridge is never carbonated even when absorbed to 5 psi. i burst back to 30 PSI every few days but always have to keep on the gas in the kegerator to finish carbing
 
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beervoid

beervoid

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I cant really help but I do know the surface area the CO2 is exposed to determines how fast the CO2 is absorbed into the beer. That is why laying a keg sideways or shaking it makes it carb faster because the surface area is increased.

If the keg is very full and the surface area of the beer is small it should take longer to get it carbonated.
This must be it then. I'll keep an eye out.
 
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beervoid

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I typically leave the gas CONNECTED at 30PSI at 34F for 2-3 days depending on the carb level desired.

I do cold crash in a mini fridge and pressurize the keg to 30psi, then disconnect. the beer in the minifridge is never carbonated even when absorbed to 5 psi. i burst back to 30 PSI every few days but always have to keep on the gas in the kegerator to finish carbing
Thats what I do and normally you can see it drop fast in about a day. These kegs with different fill levels just wont go under 22psi or so.

What type of beer are you making? and what vols are you aiming for?
Ipa and stout. Typically around 2.3-2.5 vol.
 

DuncB

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@beervoid
Thanks have been waiting for this info. Given that you are pressure fermenting when you are about 10 points of SG off final set your spunding valve to the pressure that is needed for the temp and vols.
I use this calculator Beer Carbonation Calculator

Then you cold crash ( at final gravity when ferment finished ), do a closed transfer into a purged keg ( ideally having used some of the ferment gas) . I connect the keg to the fermenter to purge the starsan out and then put the spund on the keg. That way I have a higher pressure keg than the pressure in the fermenter once cold crashed . You can then use that excess pressure to drive the closed transfer.
I brew to fill my kegs with at most a litre of headspace but the closed transfer under pressure means the beer is carbonated to the correct vols straightaway. Then you just need to have the gas regulator set for your dispensing vols and pressure. Works a treat. You only need to use gas from the cylinder to serve.
 
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beervoid

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@beervoid
Thanks have been waiting for this info. Given that you are pressure fermenting when you are about 10 points of SG off final set your spunding valve to the pressure that is needed for the temp and vols.
I use this calculator Beer Carbonation Calculator

Then you cold crash ( at final gravity when ferment finished ), do a closed transfer into a purged keg ( ideally having used some of the ferment gas) . I connect the keg to the fermenter to purge the starsan out and then put the spund on the keg. That way I have a higher pressure keg than the pressure in the fermenter once cold crashed . You can then use that excess pressure to drive the closed transfer.
I brew to fill my kegs with at most a litre of headspace but the closed transfer under pressure means the beer is carbonated to the correct vols straightaway. Then you just need to have the gas regulator set for your dispensing vols and pressure. Works a treat. You only need to use gas from the cylinder to serve.
That would work if I wherent dry hopping after fg, I also want to keep the pressure at minimum to have a favorable environment for the yeast to cleanup and deal with hop creep asap.
Thanks for elaborating.
 

DuncB

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Are you fermenting in a keg to start with so can't add the hops under pressure. Lots of breweries now dry hopping during end of ferment and going to pressure then to keep aroma. Yeast has no trouble working under pressure in my experience ( also a 1000litre fermenter has a lot of pressure at the bottom) , you can stop the hop creep by crashing the hops out at the end of their time and dropping the yeast out.
 

DuncB

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You could carbonate down the liquid line ( fit a non return valve ) that increases the carbonation speed a lot or get a carbonation cap for the Corney keg ( if you use corneys) . Otherwise down the liquid post.
 
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beervoid

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Are you fermenting in a keg to start with so can't add the hops under pressure. Lots of breweries now dry hopping during end of ferment and going to pressure then to keep aroma. Yeast has no trouble working under pressure in my experience ( also a 1000litre fermenter has a lot of pressure at the bottom) , you can stop the hop creep by crashing the hops out at the end of their time and dropping the yeast out.
Stopping hop creep is a recipe for diacetyl and refermentation.
I rather let it finish out.

But ontopic again, I find it interesting that there is such much difference between the beers for carbonating this way.
Two beers drop to 5psi in 24h (wcipa 1.010fg) the others stuck at 22 for days on end. (2 stouts with fg of 1.026 and a 2 neipa with 1.012 and 1.009)
I checked and even the kegs with a lower fill are sitting at 22psi. When I take a sample they are undercarbonated.
So its not the matter of surface area.
Its only when I put them on constant co2 in my kegerator they begin to carb up.
 

doug293cz

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Thats what I do and normally you can see it drop fast in about a day. These kegs with different fill levels just wont go under 22psi or so.



Ipa and stout. Typically around 2.3-2.5 vol.
Two kegs, both stuck at 22 psi, makes me think your gauge is out of calibration.

The rate of CO2 absorption is proportional to the exposed surface area and the difference between the headspace pressure and the equilibrium pressure for the beer at its current temp and carbonation level. This means that as the beer absorbs CO2, the rate of carbonation goes down. If the headspace is not connected to a source of constant pressure CO2 (a tank), then as CO2 is absorbed, the headspace pressure drops, thus lowering the CO2 absorption rate. So, when not connected to a source of CO2 the rate of absorption takes a double whammy.

Regardless of the faster drop of the absorption rate with a disconnected keg, the headspace pressure will drop off rapidly. More headspace will drop slower, and less surface area will also drop slower.

Brew on :mug:
 
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beervoid

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Two kegs, both stuck at 22 psi, makes me think your gauge is out of calibration.

The rate of CO2 absorption is proportional to the exposed surface area and the difference between the headspace pressure and the equilibrium pressure for the beer at its current temp and carbonation level. This means that as the beer absorbs CO2, the rate of carbonation goes down. If the headspace is not connected to a source of constant pressure CO2 (a tank), then as CO2 is absorbed, the headspace pressure drops, thus lowering the CO2 absorption rate. So, when not connected to a source of CO2 the rate of absorption takes a double whammy.

Regardless of the faster drop of the absorption rate with a disconnected keg, the headspace pressure will drop off rapidly. More headspace will drop slower, and less surface area will also drop slower.

Brew on :mug:
I have several spunding valves which I connect to the gas in to check pressure, im sure the gauges are working fine.

But what you are saying here makes the most sense, the beers are probably lightly carbonated and thus needing more pressure to carbonate correct? I will have these kegs around for another few weeks and will be monitoring.
At some point shouldnt they reach the equilibrium of the carbonation the beer really has?
 

doug293cz

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I have several spunding valves which I connect to the gas in to check pressure, im sure the gauges are working fine.

But what you are saying here makes the most sense, the beers are probably lightly carbonated and thus needing more pressure to carbonate correct? I will have these kegs around for another few weeks and will be monitoring.
At some point shouldnt they reach the equilibrium of the carbonation the beer really has?
The headspace pressure and beer carbonation level will come to equilibrium over time. There are several variables that will affect how fast the pressure drops, but the pressure should drop continuously at an ever decreasing rate, and not stop until equilibrium is reached. There is no way you are in equilibrium at 22 psi (unless you have close to 22 psi worth of air in the headspace.)

Brew on :mug:
 
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beervoid

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The headspace pressure and beer carbonation level will come to equilibrium over time. There are several variables that will affect how fast the pressure drops, but the pressure should drop continuously at an ever decreasing rate, and not stop until equilibrium is reached. There is no way you are in equilibrium at 22 psi (unless you have close to 22 psi worth of air in the headspace.)

Brew on :mug:
Maybe im not waiting long enough? Its been over a week now. Will keep monitoring
 

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I'm pretty sure that the laws of physics haven't changed recently, so Boyles law should still apply although this is not an " ideal " situation.
If the keg is still which you suggest it is and cold, there is very little disturbance at the gas ( co2 ) and liquid ( really just a very dense gas ) interface. An equilibrium will be reached quite quickly and the gradient will take a long time to spread across the distance of the keg. You are seeing equilibrium because you aren't driving the reaction with extra CO2 molecules or rocking the keg to disrupt the surface tension.
Hop creep is the diastase in the hop breaking down sugars left in the beer and making them fermentable, provided you " drop " the hops with a good crash/ finings and you have done a diacetyl rest / temp bump at the end of fermentation you should be able to avoid hop induced creep secondary to them.
 

Beermeister32

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Lots of good info here. In a nutshell, the beer needs surface area to carbonate.

If you do a high fill on a Corny keg, it will increase time to carbonate because of the lack of surface area.
 
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beervoid

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I'm pretty sure that the laws of physics haven't changed recently, so Boyles law should still apply although this is not an " ideal " situation.
If the keg is still which you suggest it is and cold, there is very little disturbance at the gas ( co2 ) and liquid ( really just a very dense gas ) interface. An equilibrium will be reached quite quickly and the gradient will take a long time to spread across the distance of the keg. You are seeing equilibrium because you aren't driving the reaction with extra CO2 molecules or rocking the keg to disrupt the surface tension.
Hop creep is the diastase in the hop breaking down sugars left in the beer and making them fermentable, provided you " drop " the hops with a good crash/ finings and you have done a diacetyl rest / temp bump at the end of fermentation you should be able to avoid hop induced creep secondary to them.
Ill try rocking the keg and see if it changes anything. Still doesnt explain why the westcoast beers are going down very fast.
Thanks!
 

VikeMan

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What temperature are the kegs at? It takes forever to carb a room temp keg, but it sucks up the Co2 in the cold kegerator/keezer.
Higher temperatures don't slow down force carbonation. They actually speed it up slightly. But they do require higher pressures to reach "X" volumes of CO2 at equilibrium as compared with colder temperatures.
 

bracconiere

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Higher temperatures don't slow down force carbonation. They actually speed it up slightly.

i'm curious as why it takes like 15 minutes of shaking to burst at 45psi, and 80f, but only like 2-3 minutes at 45psi at 40f?

this how long it takes my co2 cylinder to lose ~1oz....?
 

doug293cz

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i'm curious as why it takes like 15 minutes of shaking to burst at 45psi, and 80f, but only like 2-3 minutes at 45psi at 40f?

this how long it takes my co2 cylinder to lose ~1oz....?
The over pressure is much higher at 40°F than at 80°F, and the over pressure is one of the variables that controls the rate of carbonation. And, as carbonation proceeds, the over pressure at 80°F the over pressure drops off faster than it does at 40°F, so the rate slows down faster at the higher temp. The rate starting out slower, and slowing down faster as things proceed causes things to take longer at 80°F.

For carbonation, the rate is controlled by absolute (more correctly partial) pressures, which are gauge pressure + 14.7 psi.

Say the beer starts out at 0.8 volumes at the end of fermentation. At 40°F the equilibrium pressure is 8.6 psi absolute. At 45 psi gauge, the absolute pressure is 45 + 14.695 = 59.7 psi absolute, thus the pressure difference is 59.7 psia - 8.6 psia = 51.1 psi. At 80°F the initial equilibrium pressure is 16.8 psia, and the initial pressure difference is 59.7 psia - 16.8 psia = 42.9 psi. So the initial rate of absorption at 40°F is 51.1 / 42.9 = 1.19 faster then at 80°F. If the final carb level is 2.5 volumes, then the equilibrium pressure at 40°F is 29.9 psia, and at 80°F the pressure is 52.4 psia. The pressure deltas (which control rate) at the end of the process are 59.7 - 29.9 = 29.8 psi at 40°F and 59.9 - 52.4 = 7.5 psi, and the absorption rate difference at the end is 29.8 / 7.5 = 4.0.

Brew on :mug:
 
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bracconiere

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So the initial rate of absorption at 40°F is 51.1 / 42.9 = 1.19 faster then at 80°F.

so dissolved co2 from fermentation, ~0.8vols would basicallly be standard atmosphereic pressure, add that. i don't see where 14.695, and 16.8 come from though...

well i was googling, and had an idea...if i hit the sweet spot to form 'liquid' co2 in the keg at something that would NOT blow the keg, so under say 60-70psi...would i be able to get the liquid into the keg, then just give it a day or two to settle?


damn i just saw something about 50psi, and had a crazy thought, liquid 750-1000 isn't it, duh :(

(sorry for hijacking beervoid! :mug:)


edit: and would it matter if the co2 was warm and beer cold? my co2 is usually at 80f and just the beer i'm carbing is 40f...because 1.19 times faster just doesn't seem like what i experience...
 

doug293cz

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so dissolved co2 from fermentation, ~0.8vols would basicallly be standard atmosphereic pressure, add that. i don't see where 14.695, and 16.8 come from though...

...

edit: and would it matter if the co2 was warm and beer cold? my co2 is usually at 80f and just the beer i'm carbing is 40f...because 1.19 times faster just doesn't seem like what i experience...
The rate of CO2 absorption is controlled by absolute pressure. Gauges read the difference between absolute pressure and atmospheric pressure (14.7 psia.) So, to get absolute pressure, you have to add 14.7 psi to the gauge pressure. Carbonation charts and calculators take care of that under the covers, because the only thing a brewer can measure directly is gauge pressure.

The 1.19 ratio is an estimate of the original rate difference. At room temp the rate quickly drops off as the pressure differential between the applied pressure and equilibrium pressure goes down. At chilled temp, the rate also goes down, but much slower than at room temp. As you get close to the target carb level the rate difference is closer to 4X. And the analysis here is oversimplified, so actual differences could be more or less.

Brew on :mug:
 

bracconiere

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man i just scrolled up, this is the science forum! sorry for intruding! :( (i did read it though and look forward to the scientifically explained answer)

i'll trying to googling sugar solutions and carbonation as a parting thought...
 
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