Pressure in keg falling off at start

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doug293cz

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This assertion really makes no sense. Use any brewing software or online carbonation tool. We need less CO2 when the beer is cold to carbonate to the desired level vs needing more CO2 when the beer is warm (warmer than the cold beer) to get the same level of carbonation.

For example.

My uncarbonated beer is at 38F. I want it carbonated to 2.3 levels of CO2. At 38F I set the CO2 regulator to 9.15 PSI

However, if my uncarbonated beer is at 68F, then I'll need to set the CO2 regulator to 24.51 PSI to achieve the same 2.3 volumes of CO2.
You are confusing rate of absorption vs. maximum amount absorbed. The rate of CO2 absorption is lower at lower temps because diffusion is slower at lower temps. The maximum amount absorbed is higher at lower temps for any given CO2 partial pressure, because the CO2 solubility is higher at lower temps.

Brew on :mug:
 

Tobor_8thMan

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Go 97 miles and take a right...
You are confusing rate of absorption vs. maximum amount absorbed. The rate of CO2 absorption is lower at lower temps because diffusion is slower at lower temps. The maximum amount absorbed is higher at lower temps for any given CO2 partial pressure, because the CO2 solubility is higher at lower temps.

Brew on :mug:
No one goes by higher temp maximum amount absorbed. Please see

 

doug293cz

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No one goes by higher temp maximum amount absorbed. Please see

That has nothing to do with the physical chemistry of the process.

If someone wants to force carbonate at room temp (because they have no room available in a cooler), then they absolutely go by the maximum absorbed at room temp vs. pressure.

Brew on :mug:
 

VikeMan

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You are confusing rate of absorption vs. maximum amount absorbed. The rate of CO2 absorption is lower at lower temps because diffusion is slower at lower temps. The maximum amount absorbed is higher at lower temps for any given CO2 partial pressure, because the CO2 solubility is higher at lower temps.
Could you please provide some Minkowski diagrams for photons emitted from CO2 molecules in each case? I think that would clear it up nicely.

Also, you're right.
 

jddevinn

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Despite it's name volumes of CO2 is the space that the CO2 would take up at standard pressure (one atmosphere about 15 psia / 0 psig) and at standard temperature (32 °F). Essentially this unit is a mass.

The CO2 Volume per pressure and temperature table essentially shows the saturation amount (amount that can be absorbed) of CO2 in beer in Volumes at a specific temperature. At a steady pressure amount (Volumes) of CO2 that can be absorbed raises as the temperature falls.

Like almost every reaction the diffusion rate (time for absorption of that CO2) into the beer decreases as the temperature falls.

So in context of this conversation assuming the beer is not already saturated a small amount of CO2 at 15psig will absorb down to ~0psig quicker at a warm temperature than at a colder temperature, but it will happen at any temperature.
 

doug293cz

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Despite it's name volumes of CO2 is the space that the CO2 would take up at standard pressure (one atmosphere about 15 psia / 0 psig) and at standard temperature (32 °F). Essentially this unit is a mass.

...
It is more correct to say "CO2 Volumes" is a density (mass/volume) unit. 1 volume of CO2 is 1.977 g/L or 0.264 oz/gal.

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jddevinn

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It is more correct to say "CO2 Volumes" is a density (mass/volume) unit. 1 volume of CO2 is 1.977 g/L or 0.264 oz/gal.

Brew on :mug:
By essentially a mass unit I mean vs a volume unit, it does not have to be accompanied by a pressure & temperature to determine it's affect in calculations. So in 'thought math' it can be considered as a mass. But yes it is more accurate a density :mug:
 

doug293cz

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By essentially a mass unit I mean vs a volume unit, it does not have to be accompanied by a pressure & temperature to determine it's affect in calculations. So in 'thought math' it can be considered as a mass. But yes it is more accurate a density :mug:
If you have 2.75 oz of CO2 in your beer, how many "volumes" of CO2 is that?

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jddevinn

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If you have 2.75 oz of CO2 in your beer, how many "volumes" of CO2 is that?

Brew on :mug:
Of course you know the answer. Depends on how much beer. 10.4 Volumes/gallon. Assuming 5 gallons 2.1 Volumes.

But I didn't need to know the pressure or temp to know that. Similar to say volumetric flow of gas given in SCFM, not really a mass but in terms of your variable set can be treated as a "mass unit" not a "volume unit." Maybe referring to design variables that way is industry specific. If someone wants me to design a condenser and gives me volumetric flows I'm going to approach it one way; if someone gives me SCFM, mass flows, partial pressures, molar ratios, ect. I'm going to approach it another.

In the context of this thread I was stating that a small headspace at a higher pressure may absorb quicker than a large headspace at lower pressure because there is less mass even the the volume at lower pressure is larger. And with the name "Volumes" it's easy to confuse and think that Volumes is a volume CO2 to volume beer ratio that is dependent on the pressure/temp that you carbonate at, not that the pressure/temp is a saturation point. I think confusion over this is why there are so many variations of burst carbonation around.
 
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doug293cz

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Of course you know the answer. Depends on how much beer. 10.4 Volumes/gallon. Assuming 5 gallons 2.1 Volumes.

But I didn't need to know the pressure or temp to know that. Similar to say volumetric flow of gas given in SCFM, not really a mass but in terms of your variable set can be treated as a "mass unit" not a "volume unit." Maybe referring to design variables that way is industry specific. If someone wants me to design a condenser and gives me volumetric flows I'm going to approach it one way; if someone gives me SCFM, mass flows, partial pressures, molar ratios, ect. I'm going to approach it another.

In the context of this thread I was stating that a small headspace at a higher pressure may absorb quicker than a large headspace at lower pressure because there is less mass even the the volume at lower pressure is larger. And with the name "Volumes" it's easy to confuse and think that Volumes is a volume CO2 to volume beer ratio that is dependent on the pressure/temp that you carbonate at, not that the pressure/temp is a saturation point. I think confusion over this is why there are so many variations of burst carbonation around.
Now, if I tell you you have 0.686 oz/gal of CO2, how many "volumes" of carbonation do you have?

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jddevinn

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If I say I have a bottled pint of beer at 2.2 Volumes you'll know the mass of CO2 (other than arguments over pint vs pint)in solution, but you won't know the actual volume of the CO2 in solution without also knowing the internal pressure and temperature.
 

jddevinn

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are you calculating residule co2 from fermentation? i'm curious, does co2 have calories? i try to calculate to the nearest 10, but now i wonder if i'm burst carbing...if maybe i need to compensate for the co2?
Total CO2. We're just talking about my use of 'mass unit'. :mug: You will have residual CO2 from fermentation but it will be process and equipment dependent. It can't have much calories because it doesn't contain much energy.
 

doug293cz

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If I say I have a bottled pint of beer at 2.2 Volumes you'll know the mass of CO2 (other than arguments over pint vs pint)in solution, but you won't know the actual volume of the CO2 in solution without also knowing the internal pressure and temperature.
If I have a value, and I have to multiply that value by volume in order to know the mass of material that the value represents, then the value has units of density.

Brew on :mug:
 

Vale71

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This assertion really makes no sense. Use any brewing software or online carbonation tool. We need less CO2 when the beer is cold to carbonate to the desired level vs needing more CO2 when the beer is warm (warmer than the cold beer) to get the same level of carbonation.
Your assertion is wrong. You need the same amount of CO2 to carbonate to a given carbonation level regardless of beer temperature. 3 vols equals 5.88 g/l of CO2 at any temperature. The only thing that changes is the headspace pressure required to push CO2 into solution and to keep it there indefinitely. This all has nothing to do with how fast equilibrium is reached.
 

Vale71

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Turning off a CO2 cylinder obviously doesn't "prevent leaks".
No, but it certainly reduces the extent of loss they may cause. The amount of CO2 that's inside a regulator is quite small compared to a full cylinder. Even if the leak were upstream of the check valve worst case would be your beer goes flat as the keg slowly depressurizes, but if you leave the shut-off valve open you may well end up needed a cylinder refill sooner rather than later.
 

TLaffey

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This assertion really makes no sense. Use any brewing software or online carbonation tool. We need less CO2 when the beer is cold to carbonate to the desired level vs needing more CO2 when the beer is warm (warmer than the cold beer) to get the same level of carbonation.
More PRESSURE at higher temps, yes. Beer absorbs CO2 faster at the higher temp, but doesn't absorb as much of it. Beer will absorb more gas at lower temps. At a constant pressure, you will have more absorbed (more carbonation) at the lower temp.
 

Vale71

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Beer absorbs CO2 faster at the higher temp, but doesn't absorb as much of it.
If you look at any carbonation chart you'll see that you can reach any carbonation level, no matter how high, at any temperature provided you set the correct equilibrium pressure. This means that beer can absorb as much CO2 at a higher temperature as it can absorb at a lower temperature. Saying that beer "doesn't absorb much of it" is simply wrong.

For the case we were discussing, i.e. pressurizing a keg at a given pressure and then shutting off the gas supply, you would observe a much faster drop in pressure at a higher temperature than at a lower temperature leading you to mistakenly thinking that there must be a leak somewhere and disassembling everything in a futile attempt to fix something that "ain't broken".
 

TLaffey

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If you look at any carbonation chart you'll see that you can reach any carbonation level, no matter how high, at any temperature provided you set the correct equilibrium pressure. This means that beer can absorb as much CO2 at a higher temperature as it can absorb at a lower temperature. Saying that beer "doesn't absorb much of it" is simply wrong.

For the case we were discussing, i.e. pressurizing a keg at a given pressure and then shutting off the gas supply, you would observe a much faster drop in pressure at a higher temperature than at a lower temperature leading you to mistakenly thinking that there must be a leak somewhere and disassembling everything in a futile attempt to fix something that "ain't broken".
Yes, I agree. My wording was clumsy.
 
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