Pressure gauge mounted in bottle cap

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I agree with what Bobby says here I was discussing why bottled conditioned beer takes longer to than just the time for the yeast to consume the sugar to be properly carbonated and have nice fine bubbles. Everyone seems to think that it was the CO2 dissolving into the beer from the head space, my opinion is that as the beer is allowed to settle and the yeast and sediment in the beer drop from solution that their is less nucleation sites for the CO2 to come out of solution and hence a finer bubble. The CO2 is excreted by the yeast into solution one molecule at a time the excess dissolved beer is off gassed into the head space.

CO2 in the head space of a carboy vs CO2 in the beer is extremely complicated when you look at the law of partial pressures and the affect of gasses exchanging through the water/alcohol in the air lock and the back pressure of gasses caused by the airlock it is enough to make you go crazy. This effects your carbonation level as the dissolved CO2 concentration is added to your total CO2 in most priming calculators.

If you ever want to see the law of partial pressures in action get one of those stupid pump caps that someone thought would allow you to keep soda carbonated by pumping atmospheric air into the head space of a opened soda bottle.

http://www.amazon.com/dp/B00004XSH3/?tag=skimlinks_replacement-20

It does not take into account that air is only 1% CO2, when I saw those in the super market I thought that was so funny, it was a tax for those people who were not listening in chemistry class.

Ever since I switched to 1/2 liter swing-top bottles, I've been having trouble with over carbonation and gushering, even after 2months in the bottle.I'm beginning to think I'm not leaving enough head space. With 12 oz. bottles, I would just use the displacement of the bottling wand to set the correct headspace. Does that work with larger bottles or should I leave a bit more?

Head space to beer ratio matters, I think the less head space the better as then you have less O2 in the beer during the bottling process but back off your sugar to get the desired results. All the pressure in the bottle is equal through out liquid and gas, if your head space is the same volume (determined by the bottle wand) and you are producing the same amount of CO2 your pressure will be higher.

Think of it like this 12oz bottle = 12 oz of beer with a set amount of sugar produces X volumes of CO2. 24oz of beer with the same concentration of priming sugar with produce 2X volumes of CO2. Now the head space has stayed the same so the ratio has been increased resulting in higher pressure. It is a lot more complicated than that as you have to throw in there how much space the water (beer) molecules take up so that will further skew the pressure relationship, throw in temp changes effecting the CO2 solution and it is really complicated. I don't know of a priming calculator for different size bottles but I would start with backing off the sugar concentration by 5 to 10% to start with and see how it goes. I enjoy my beer on the lower side of the carbonation style so I would rather under shoot than over shoot.

Clem
 
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In no way would the headspace ever have a higher concentration of CO2 than the beer in which it originated. The yeast don't swim to the surface to fart.
I don't claim to know the science, but didn't someone here put a pressure gauge on a bottle and record the pressure during the carbonation process at a constant temperature? What I thought I read is that the pressure peaked and then dropped.

My conclusion from this would be that it is similar to pumping CO2 in through your out tube in a keg. You don't get much benefit from it because the CO2 first rises to the head space and then reaches equilibrium over time. I'd think that naturally carbonating is the same. The yeast consumes sugars and produces CO2 which goes into the head space and raises the pressure there. Over time it comes into equilibrium with the fluid.

The yeast don't swim to the surface and fart. It's more farting in the bath tub. The first thing it does it bubble up to the surface and stink up the room. :D

But this is me being an armchair scientist. It could be like Bobby say. That the CO2 is absorbed as quickly as it is produced.
 
It sounds like a good timelapse experiment to me. The most important thing to me is making sure that temperature variations are not affecting the pressure. The way to do it would be to run thermowell and log temps along with pressure.

I think the most non-intuitive part of this thing is thinking at a molecular level. We often visualize CO2 in terms of bubbles. In order for a CO2 bubble to form, the pressure differential has to be pretty significant. If you bottle a light/clear beer in a clear glass bottle, you won't ever see bubbles.
 
After reading this thread I am still confused :confused: Would the mounted psi gauge on top of the bottle not be a great way to monitor the pressure exerted on the bottle from within during the fermentation phase?
I am thinking this would be a simple way to monitor pressure when doing batches of ginger beer in PET bottles, that is, wait 'til the guage reads 40-50 psi and then you know it's time for a cold crash vs the old 'squeeze it and see how hard it is method.' :cross: Am I right thinking along these lines, or did I miss something?
 
We're in a closed system. As yeast metabolize the sugar and create CO2, the concentration of CO2 in the beer is immediately higher than that of the headspace, let's say .8 volumes... diffusion is about to make the headpace equal and so on. In no way would the headspace ever have a higher concentration of CO2 than the beer in which it originated. The yeast don't swim to the surface to fart.

I don't think that's quite correct. Even in a closed system there can be a substantial difference in CO2 distribution. Take a bottle or can of soda and shake it up for a minute. The agitation will cause a lot of the CO2 to come out of solution and into the headspace, making the bottle/can much more firm from the additional pressure. The greater internal pressure relative to atmospheric pressure is what causes it to foam if opened before it has time to reabsorb the CO2.

I am thinking this would be a simple way to monitor pressure when doing batches of ginger beer in PET bottles, that is, wait 'til the guage reads 40-50 psi and then you know it's time for a cold crash vs the old 'squeeze it and see how hard it is method.' :cross: Am I right thinking along these lines, or did I miss something?

I've never made ginger beer, but it sounds like a good plan to me.
 
It sounds like a good timelapse experiment to me. The most important thing to me is making sure that temperature variations are not affecting the pressure. The way to do it would be to run thermowell and log temps along with pressure.

From another thread here-
56596d1334186331-beer-bottle-pressure-tester-dry-dock-paragon-apricot-blond-bottle-pressure.jpg


Even though there's no temp log, the person who posted this mentioned that it was in a home with the thermostat set to a low of 65° and a high of 72°. The daily temp fluctuations are fairly obvious, but it's hard to know how much the temp was really changing. The difference in pressure between 65° and 72° would be ~3.5 psi, but the difference between the peak and where the pressure settled appears to be closer to 6 psi. Unless the bottle developed a tiny leak, there was more going on to create that rise and fall trend than simply temperature fluctuations.
 
JuanMoore said:
I don't think that's quite correct. Even in a closed system there can be a substantial difference in CO2 distribution. Take a bottle or can of soda and shake it up for a minute. The agitation will cause a lot of the CO2 to come out of solution and into the headspace, making the bottle/can much more firm from the additional pressure. The greater internal pressure relative to atmospheric pressure is what causes it to foam if opened before it has time to reabsorb the CO2.

I've never made ginger beer, but it sounds like a good plan to me.

Disagree. A bottle of sealed soda has co2 at equilibrium. Shaking does not pull co2 out of solution because it can't. The partial pressure in the headspace and the newly formed bubbles already matches that of the dissolved co2. The reason it gushes after shaking is that the bubbles create nucleation point similar to mentos in diet coke.
 
JuanMoore said:
From another thread here-

Even though there's no temp log, the person who posted this mentioned that it was in a home with the thermostat set to a low of 65° and a high of 72°. The daily temp fluctuations are fairly obvious, but it's hard to know how much the temp was really changing. The difference in pressure between 65° and 72° would be ~3.5 psi, but the difference between the peak and where the pressure settled appears to be closer to 6 psi. Unless the bottle developed a tiny leak, there was more going on to create that rise and fall trend than simply temperature fluctuations.
I peg the pressure spike on temperature. There are two factors that have not come up on that graph. The first is that fermentation is exothermic so the thermostat controlling ambient temps doesnt tell us enough. Also, there is plenty of variance in temps in a house well outside the thermostat range, e.g. drafts and radiant heat from windows. Last, spikes in temp are going to affect the headspace quicker due to the heat capacity difference from liquid.

Long story short, the experiment must be repeated with the bottle in a water bath with temp logging along with pressure. The results will probably change.
 
Long story short, the experiment must be repeated with the bottle in a water bath with temp logging along with pressure. The results will probably change.

How funny that I just read this tonight as I finish bottle conditioning another batch with this setup. I did use a water bath this time, but it had limited effect on the pressure fluctuations. I think the fact that I did not cover the headspace part of the bottle let that part continue to fluctuate temps. And unfortunately I did not record temps (again!) - there's always next time. I'll post the data later. I'm still a little perplexed about the apparent overshoot, then undershoot and recovery in the first data set. I still wonder if the absorption function is such that it creates a longer term ringing and settling. This would be more apparent if I passed the data through a filter to attenuate the 24 hour signal. I guess the absorption function is a mass transfer problem and can be mathematically pretty complicated. Of course that view is consistent with the idea that pressure forms faster in the headspace, then gets absorbed toward equilibrium. I feel like that view could be right because of the fact that the process of the gas coming out of solution is easier/faster than getting it back in.
 
I peg the pressure spike on temperature.
I did go on weather underground to get external temps for my area from that timeframe, but my recollection is that when I graphed them together with pressure there wasn't any obvious correlation. However, I agree that other phenomena (drafts, etc) could have contributed. Ultimately I need to measure ambient temps - and maybe do a better job controlling them.
 
Here is the data from this batch. One procedural differences to highlight ... This time I switched to a wider bottling wand which left more headspace than last time (probably double the headspace as last time, about 2"). I'll probably go back to the narrower bottling wand b/c I don't like that much headspace.

Now some comments on the data. Near the beginning there is about 12 hours of missing data where the monitor crapped out. Think I know what happened and how to avoid it next time.

The initial pressure rise was really fast.

I don't really know why, but the pressures never really reached where I would have expected. I doubt it can be attributed to the increased head space. If the data is right then the CO2 in this bottle is about 1.5 volumes. I'll say that other bottles from this batch are properly carb'ed - definitely more than 1.5 volumes. I haven't cracked the monitoring bottle yet.

I do see some similar artifacts as last time (besides the 24 hour cycle) - looks like overshoot, then oscillations settling to a mean.

I'll also mention that today we did not have the AC on and local outdoor temps reached 80. That's the probable reason for the last spike.

Any thoughts on what I should do differently next time? I may have to put the bottle in my fermentation chamber to keep the temp more constant. This water bath was not a temp controlled bath - just more thermal mass to try to slow the swings and apparently wasn't very effective. I'll also see if I can get a temp recording. Would be cool to have a gravity reading too, but I can't imagine how to do that.

Trigo Oscuro - Bottle Pressure.jpg
 
I think having an RTD in a thermowell inside the beer and logging those temps would be ideal. One thing I suspected could be happening is that your bottle seal, or the bulkhead you put in is only capable of holding 10 psi and any more than that, it tweaks the seal letting some gas escape. That would explain the oscillation if it is not directly correlated to beers temps. I don't know how exothermic this mild fermentation is.
 
One thing I suspected could be happening is that your bottle seal, or the bulkhead you put in is only capable of holding 10 psi and any more than that, it tweaks the seal letting some gas escape. That would explain the oscillation if it is not directly correlated to beers temps.

I thought about this some more and tried another experiment. I used a couple of alka seltzer tablets and a small amount of water in the bottle to build pressure and test for leaks. The small amount of water was so that I wouldn't see much effect from CO2 being lost/dissolved back into the water. Some background: The cap I made uses a kork-n-seal resealable cap (see http://www.sha.org/bottle/closures.htm about midway down for a picture). I picked up some of these that were in excellent unused condition. I took this route b/c I wanted to use a glass bottle and a re-usable cap. Anyway, when I ran the leak experiment, it didn't seem like the pressure went as high as I would have predicted. When I picked up the bottle and placed pressure on the lever, I heard a hiss. I ran the experiment again and overnight the pressure dropped from about 15 PSI to 4 PSI. Definitely a leak existed. I examined the rubber seal and found that it was pretty compressed and had a slight amount of residue underneath it. I think it was the original seal in the bottle cap (prob circa 1960!). I replaced it with a new hose washer which is a slight bit thicker and made with more modern material. The lever now resists more and snaps into place. I started another experiment on this new cap and it's held 22 PSI for over 24 hours now.

I suspect the leak developed on the second batch and got even worse when I tried these leak experiments. I'm not sure about the first dataset. It seems like a leak would be more intermittent and faster. But anyway, no way telling until I run the priming experiment again. This time I'll pre-test the cap to 30 PSI and I might just switch to a plastic bottle/screwtop.

I think having an RTD in a thermowell inside the beer and logging those temps would be ideal.

That shouldn't be too hard. But I would probably change to a PET bottle if the sensor had to be in the beer. However, I think it would be good enough to tape a sensor to the outside of the bottle and insulate it.

I don't know how exothermic this mild fermentation is.
I would guess it's not very exothermic. I'd be surprised if it raised the temp by more than 1F.
 
I did go on weather underground to get external temps for my area from that timeframe, but my recollection is that when I graphed them together with pressure there wasn't any obvious correlation. However, I agree that other phenomena (drafts, etc) could have contributed. Ultimately I need to measure ambient temps - and maybe do a better job controlling them.

I guess I'm not really sure what I did back then :) ... but, I went back and graphed average outdoor temps vs pressure and there does appear to be some correlation. I still want to run the experiment with more temp control and recording just to see if this is all due to temps. I also filtered out the signal with 24 hr period in this data.

Dry Dock Paragon Apricot Blond - Bottle Pressure - 24hr filt + outdoor temps.jpg
 
Disagree. A bottle of sealed soda has co2 at equilibrium. Shaking does not pull co2 out of solution because it can't. The partial pressure in the headspace and the newly formed bubbles already matches that of the dissolved co2. The reason it gushes after shaking is that the bubbles create nucleation point similar to mentos in diet coke.

Shaking can pull it out of solution because nucleation (from energy input spent shaking) IS causing CO2 to escape from the liquid (evidenced by the bottle hardening) and it is not being replaced back into solution at the same rate, and therefore it is no longer in a state of equilibrium. Equilibrium doesn't imply that two things are equal, it just means that reactions going both directions are happening at the same rate. After shaking the bottle and causing CO2 to escape from solution, there is excess CO2 in the headspace above the liquid due to the energy put into shaking the bottle, and according to Le Chatelier's Principle, after the shaking has stopped (no more energy input on reactant's side), excess products on one side will cause the reaction to shift so that more reactants are created. Basically, CO2 will begin dissolving faster than it is escaping the liquid. But it still takes time for equilibrium to be established again. CO2 is CONSTANTLY seeping out of the liquid and being absorbed. In equilibrium, these rates are the same. When you put in energy (such as shaking), you are disrupting the equilibrium. This principle also explains the effect of temperature, because the K value changes with it.

EDIT: here's a picture

carb.jpg
 
Shaking can pull it out of solution because nucleation (from energy input spent shaking) IS causing CO2 to escape from the liquid (evidenced by the bottle hardening) and it is not being replaced back into e and causing CO2 to escape from solution, there is excess CO2 in the headspace above the liquid due to the energy put into shaking the bottle, and according to Le Chatelier's Principle, after the shaking has stopped (no more energy input on reactant's side), excess products on one side will cause the reaction to shift so that more reactants are created. Basically, CO2 will begin dissosolution at the same rate, and therefore it is no longer in a state of equilibrium. Equilibrium doesn't imply that two things are equal, it just means that reactions going both directions are happening at the same rate. After shaking the bottllving faster than it is escaping the liquid. But it still takes time for equilibrium to be established again. CO2 is CONSTANTLY seeping out of the liquid and being absorbed. In equilibrium, these rates are the same. When you put in energy (such as shaking), you are disrupting the equilibrium. This principle also explains the effect of temperature, because the K value changes with it.

EDIT: here's a picture


I'm not biting on this just yet. Have you ever put a pressure gauge on a sealed carbonated container, noted the pressure at stasis and then noted a pressure increase after shaking? If you haven't but know of a video or paper where it has been documented let me know.

http://www.phys.csuchico.edu/kagan/profdev/soda.pdf

I don't know why you would suggest that shaking in a closed system disrupts equilibrium. Le Châtelier's Principle requires that you change something like temperature, pressure or concentration. Shaking does none of this.
 
OK, trial 3 is finally done. It turned out to be a pretty tasty beer too! (afterall, this really is still about making beer) It started as a Goose Island Mild Winter clone, but I decided to add a little more rye than normally recommended. I tastes nice, but I know I wouldn't add any more rye than I did.

Anyway about the experiment. I built an entirely new cap/bulkhead to try to eliminate the leak issue:

Pressure Monitor.jpg

I pressure tested it to 49 PSI for about 2 days and it didn't appear to leak at all:

Bottle Pressure Monitor - Pressure Test Data.png

The priming was carried out in my fermentation chamber at around 70 F for 3 weeks. It does look like the pressure built to a plateau of 39 PSI and then diminished to settle at 35 PSI. The priming sugar amount should have put this at 2 volumes. At 72 F (as measured) that should have make a pressure of about 23 PSI at equilibrium. This is obviously well above that.

Mild Winter Clone Bottle Priming Pressure.png

Mild Winter Clone Bottle Priming Temperature.png
 
I don't know why you would suggest that shaking in a closed system disrupts equilibrium. Le Châtelier's Principle requires that you change something like temperature, pressure or concentration. Shaking does none of this.

Pressure is changing when the bottle is shaken. It is obvious because the walls of the container become harder to move, because there are more molecules of gas in the headspace colliding against the container's walls. I don't see what more evidence you need. Given time, equilibrium will become reestablished and the container will return to the original hardness.

I think that your assumption of a closed system is a false premise. Closing something off in a bottle doesn't shut the system off from the universe, as I can shake it, heat it, pass light through it, make gas come out of solution, etc. As CO2 leaves solution, the concentration has changed, and thus the equilibrium shifts.

Look at the graphs above. See the dip off in pressure? That indicates that at some point in time the pressure was higher than the pressure at equilibrium. That is because initially the yeast were producing CO2 in solution (reactants). This causes the reaction to shift to create more products. After the yeast have ceased making reactants, the reaction shifts back towards creation of the reactants (because of the excess products that were made earlier..indicated by the beginning of the 'dip'), and eventually equilibrium is reached (meaning that the creation of reactants and products is happening at the same rate).
 
Pressure is changing when the bottle is shaken. It is obvious because the walls of the container become harder to move, because there are more molecules of gas in the headspace colliding against the container's walls. I don't see what more evidence you need. Given time, equilibrium will become reestablished and the container will return to the original hardness. I think that your assumption of a closed system is a false premise. Closing something off in a bottle doesn't shut the system off from the universe, as I can shake it, heat it, pass light through it, make gas come out of solution, etc. As CO2 leaves solution, the concentration has changed, and thus the equilibrium shifts.

When I first saw this discussion, I tried this out, and I have to say that I did not notice any change in pressure by feel in a 16 oz pop bottle. It wouldn't be too hard to use measurement system like this to see if there is any pressure change from shaking.
 
OK, trial 3 is finally done. It turned out to be a pretty tasty beer too! (afterall, this really is still about making beer) It started as a Goose Island Mild Winter clone, but I decided to add a little more rye than normally recommended. I tastes nice, but I know I wouldn't add any more rye than I did.

Anyway about the experiment. I built an entirely new cap/bulkhead to try to eliminate the leak issue:

View attachment 97711

I pressure tested it to 49 PSI for about 2 days and it didn't appear to leak at all:

View attachment 97707

The priming was carried out in my fermentation chamber at around 70 F for 3 weeks. It does look like the pressure built to a plateau of 39 PSI and then diminished to settle at 35 PSI. The priming sugar amount should have put this at 2 volumes. At 72 F (as measured) that should have make a pressure of about 23 PSI at equilibrium. This is obviously well above that.

View attachment 97708

View attachment 97709

This is an excellent effort. Did you ever explain where the temp probe was? I still think that the spike may be influenced by temperature or some other anomaly. I was searching for the thread that showed anoldUR's similar experiment and he didn't get the spike. It would be nice to figure out they the results vary.
 
Pressure is changing when the bottle is shaken. It is obvious because the walls of the container become harder to move, because there are more molecules of gas in the headspace colliding against the container's walls. I don't see what more evidence you need. Given time, equilibrium will become reestablished and the container will return to the original hardness.

It is not obvious to me because I do not feel the walls of a soda bottle get firmer when I shake. What makes you think the CO2 molecules are coming out of solution faster than they are reentering? What would convince me is to measure pressure at stasis, shake and measure again.
 
This is an excellent effort. Did you ever explain where the temp probe was? I still think that the spike may be influenced by temperature or some other anomaly. I was searching for the thread that showed anoldUR's similar experiment and he didn't get the spike. It would be nice to figure out they the results vary.

Thank you.

You've probably sensed that I'm not ready to draw any conclusions just yet.

For one, the shape of the decay doesn't look like what I might expect. I suppose to really rule out leaking, I'd have to run a big study to establish how likely it is to leak (gasket placement, screw torque, etc) or get a CO2 detector. Neither of those is going to happen :)
Based on the results of the leak test I'm fairly confident in the capability to avoid leaks.

The temperature measurements came from an RTD with very small thermal mass (Auber Instruments) which was tucked behind that spounge you see in the picture. I decided against a true thermowell because of how complicated (with my skills anyway) it would have been to construct.

While I was getting ready to run the experiment, I thought about the physics behind the problem and I was convinced that the "rise to a peak, then fall" phenomena could happen, given one assumption. If the yeast generated CO2 faster than the surrounding liquid could absorb it, given the current equilibrium conditions), then it would evolve (not bubble) off and pressurize the headspace, then go back to equilibrium. But honestly I didn't study the absorption/evolution rate vs yeast CO2 production rate rate enough to know whether this was possible.

Absorption is a pretty slow process (as seen by common kegging practice) and evolution is a relatively fast process (as seen by the small amount of time it takes a beer/pop to go flat).

Your point about the other graphs people have drawn is a good one, which I had considered before I ran the experiment the third time. Up until 1/26, I just figured that my experiment was saying the same thing as theirs. But once the pressure started going down the question opened back up.
 
It is not obvious to me because I do not feel the walls of a soda bottle get firmer when I shake. What makes you think the CO2 molecules are coming out of solution faster than they are reentering? What would convince me is to measure pressure at stasis, shake and measure again.

I went to the store today and bought a soda bottle, just to be sure about this. Cracked it open and closed it back up tightly. The bottle was very easy to squeeze. I shook it up and now it is incredibly firm. The only explanation is that shaking caused gas to come out of solution. I don't think that there is any other explanation as to why the container is firm.
 
I went to the store today and bought a soda bottle, just to be sure about this. Cracked it open and closed it back up tightly. The bottle was very easy to squeeze. I shook it up and now it is incredibly firm. The only explanation is that shaking caused gas to come out of solution. I don't think that there is any other explanation as to why the container is firm.

Did it get warmer?
 
Did it get warmer?

On a molecular level, molecules are colliding with each other and transferring kinetic energy to each other. Some have higher amounts than others. The heat is proportional to the average of the kinetic energy of all of the molecules in the solution. So the shaking may have increased the overall kinetic energy, but I doubt that a typical thermometer would show any difference in temperature. But who knows? Maybe it would..sounds like another experiment :D
 
I could do this test really quickly buy just filling my bottle w/gauge (see post #1 ), capping, shaking, and watching the needle.

Please do, as your cool device using numbers would probably be more convincing than my 'container feels much harder' evidence.
 
I went to the store today and bought a soda bottle, just to be sure about this. Cracked it open and closed it back up tightly. The bottle was very easy to squeeze. I shook it up and now it is incredibly firm. The only explanation is that shaking caused gas to come out of solution. I don't think that there is any other explanation as to why the container is firm.

When you opened the cap you released the pressure in the headspace and altered the system. To restore equilibrium some of the CO2 would have to migrate from the solution to replace the loss of pressure in the headspace. This would be accelerated by shaking.
 
When you opened the cap you released the pressure in the headspace and altered the system. To restore equilibrium some of the CO2 would have to migrate from the solution to replace the loss of pressure in the headspace. This would be accelerated by shaking.

Right, this is exactly what I was trying to prove. Equilibration takes time, and that shaking can induce gas to come out of solution. You know, crap, I should have left the bottle alone after shaking it to see if CO2 would be reabsorbed and the container would go back to being less firm. But, I drank it :( Though, I think we all know what happens when you shake someones can/bottle of soda. You have to let sit for several minutes so that equilibrium can be reestablished.
 
You know after thinking about it, the little soda bottle experiment did prove that you can shake gas out of solution, but it didn't answer the question if shaking will bring it out of solution for a system that is already in stasis...The reason I cracked it open was because upon purchasing the bottle was ridiculously hard already and I wouldn't be able to tell if there was a difference just by feeling it. One of you guys with the pressure gauges, maybe you should let a filled bottle of soda sit until the pressure gauge doesn't change anymore, and then shake the bottle and see if there is a change.
 
No carbonated beverage increases in pressure when shaken, not even Champagne, but the increase of nucleation sites allows the gas to rush out more quickly and with more liquid in foamy tow: http://www.phys.csuchico.edu/kagan/professional/papers/soda.pdf, http://tinyurl.com/serwayjewett
After opening the container, closing and shaking it helps the bottle reach a new equilibrium.

Yeast farts on the molecular level, producing 2CO2 at a time, each about 0.3 nanometers long. As they are produced throughout the beer they are absorbed into it, and the headspace, in equilibrium. CO2 absorption is very slow as it occurs through diffusion (http://en.wikipedia.org/wiki/File:Chemical_surface_diffusion_slow.gif). The data in this thread suggests that at peak fermentation CO2 could form faster than the beer can absorb it, disrupting equilibrium and collecting in the headspace. I can't find studies on CO2 formation vs absorption in beer, but it would definitely vary with yeast strain, alcohol %, and temperature.
 
No carbonated beverage increases in pressure when shaken, not even Champagne, but the increase of nucleation sites allows the gas to rush out more quickly and with more liquid in foamy tow: http://www.phys.csuchico.edu/kagan/professional/papers/soda.pdf, http://tinyurl.com/serwayjewett
After opening the container, closing and shaking it helps the bottle reach a new equilibrium.

Yeast farts on the molecular level, producing 2CO2 at a time, each about 0.3 nanometers long. As they are produced throughout the beer they are absorbed into it, and the headspace, in equilibrium. CO2 absorption is very slow as it occurs through diffusion (http://en.wikipedia.org/wiki/File:Chemical_surface_diffusion_slow.gif). The data in this thread suggests that at peak fermentation CO2 could form faster than the beer can absorb it, disrupting equilibrium and collecting in the headspace. I can't find studies on CO2 formation vs absorption in beer, but it would definitely vary with yeast strain, alcohol %, and temperature.

Well damn. It looks like I was wrong about the shaking of a liquid in equilibrium bringing out gas. I'd still like to see one of you guys with a pressure gauge cap shake a carbonated liquid in equilibrium just for fun though to validate it :mug:

The data does however seem to show that the headspace can have more CO2 than it would normally have at equilibrium while it is carbing up though.

If yeast are producing CO2 and releasing it one molecule at a time, it seems that it would be dissolved pretty easily, and that for any gas to build up into the headspace, it would first have to 'un-dissolve'. If this were true, then there would never be more gas in the headspace...but the data shows otherwise.

It makes me curious about the underlying assumption. While CO2 is made in quantified amounts during metabolism, is it actually released from the cell the same way? I know gas can diffuse through a cell membrane freely, but does that imply that it is one CO2 molecule at a time? A quick google search didn't turn up anything for the mechanism of CO2 exiting a yeast cell.
 
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