Closed Transfer: What About the Jumper Lines?

[Yesfan]

On a unrelated topic......I'm pretty sure the Kegland disconnects (red/grey gas & black/yellow beer) are universal. I know they are with the Kegland colored posts on my All Rounder fermenter. You'd think they would still be post specific for your run of the mill corny. One of the gas disconnects (the red/grey one) I could swap between each post with no effort. The old school CMB style disconnects only work one way (grey to gas, black to beer).

I wished I'd known this when I ordered my universal posts for my kegs. The Kegland disconnects are $2 cheaper than the universal posts and you don't have to have the adapter to use them with the EVA barrier lines.

 

[Bassman2003]

Yes, it is very nice to have the disconnects that are made to interface with EVA tubing.

 

[AlexKay]

I’ve had some trouble with them. Gas ones not fitting on posts, liquid ones not releasing poppets when you take them off (mess!)

 

[Yesfan]

I’ve had some trouble with them. Gas ones not fitting on posts, liquid ones not releasing poppets when you take them off (mess!)

With what? Universal posts? Poppits? Kegland's disconnects? Don't know if you're replying specifically to me so thought I'd ask.

The set of universal posts/poppits I put on one of my kegs seem to work. I pressure tested it and it's still sitting at 10psi. I think the universal posts don't work with all kegs (according to More Beer), but most of my kegs are Super Champion and Challenger VI cornys if that helps.

 

[AlexKay]

With what? Universal posts? Poppits? Kegland's disconnects? Don't know if you're replying specifically to me so thought I'd ask.

The set of universal posts/poppits I put on one of my kegs seem to work. I pressure tested it and it's still sitting at 10psi. I think the universal posts don't work with all kegs (according to More Beer), but most of my kegs are Super Champion and Challenger VI cornys if that helps.

Kegland disconnects. They're sleek and low-profile, but both gas and liquid have given me problems.

 

[Yesfan]

Kegland disconnects. They're sleek and low-profile, but both gas and liquid have given me problems.

Gotcha. I'll keep an eye on mine then. Appreciate the heads up.

 

[Bassman2003]

I have had good experiences with the normal disconnects. I ordered two of the plastic adjustable type and they do not seem to create a good seal as I had bubbles and foam in the keg lines. I am still checking them out but have been too busy to dive in. My stainless adjustable from Kegland works great.

 

[segallis]

Even if the ambient air pressure is far less than the CO2 pressure in the line, you will still get O2 going into the line, into the CO2 filled area.

The reason is because, strictly from the standpoint of the O2, there's some O2 outside of the line and therefore some O2 pressure outside of the line. But none inside the line. Lots of Co2 pressure inside, but no O2 pressure inside. And so the O2 will indeed permeate through the line and get inside until it balances out.

I would like to understand the physics behind this. If you are correct then it would seem any additional O2 molecules introduced into the higher pressure CO2 line would increase the pressure even further (more moles of gas total), which would seem to violate the Boyle's Law (among others). Everything I have read on permeability and diffusion seems to imply the pressure would cause things to move the opposite direction. E.g. This is how some gas separators work. In fact, Nitrogen would be much more likely to permeate into the line since it is both much more concentrated/higher partial pressure and also a lighter molecule. Obviously, without a pressure difference, an area of greater oxygen concentration would tend to move into an area of lower concentration (all the gases would mix in both directions until the partial pressure of each component is equal).

Actually, this entire thread and things like agonizing over ppm's of O2 and purging jumper lines with one thousandth the total volume has me wondering how people have actually been enjoying cask ales for thousands of years, not to mention the recent explosive popularity of barrel aged beers.

 

[mac_1103]

I would like to understand the physics behind this.

Google "partial pressure."

Actually, this entire thread and things like agonizing over ppm's of O2 and purging jumper lines with one thousandth the total volume has me wondering how people have actually been enjoying cask ales for thousands of years

It's true that people have been enjoying beer for thousands of years, but people have also been putting up with flat oxidized beer for most of that time.

 

[AlexKay]

I would like to understand the physics behind this. If you are correct then it would seem any additional O2 molecules introduced into the higher pressure CO2 line would increase the pressure even further (more moles of gas total), which would seem to violate the Boyle's Law (among others). Everything I have read on permeability and diffusion seems to imply the pressure would cause things to move the opposite direction. E.g. This is how some gas separators work. In fact, Nitrogen would be much more likely to permeate into the line since it is both much more concentrated/higher partial pressure and also a lighter molecule. Obviously, without a pressure difference, an area of greater oxygen concentration would tend to move into an area of lower concentration (all the gases would mix in both directions until the partial pressure of each component is equal).

Actually, this entire thread and things like agonizing over ppm's of O2 and purging jumper lines with one thousandth the total volume has me wondering how people have actually been enjoying cask ales for thousands of years, not to mention the recent explosive popularity of barrel aged beers.

Maybe this will help frame the problem.

There's no question what the equilibrium state is for this system: the gas mixture inside and outside the tube will be the same composition and pressure. The only question is how long it takes for this to happen, and that depends on the tube's permeability: an impermeable metal tube will keep equilibrium from ever occurring, whereas a highly permeable silicone tube will let you get there relatively quickly. On the way to equilibrium, a CO2-filled tube will leak CO2 out into the atmosphere, at the same time as O2 (and yes, N2) from the atmosphere diffuse in.

The counter-intuitive case you're proposing is that diffusion into a tube increases its pressure. In most cases this won't happen, because other gases will be diffusing out at the same time. In the extreme cases (say, helium through a glass tube), it does indeed happen, but to say that things get counter-intuitive in extreme cases doesn't refute the underlying principles.

Diffusion through a permeable polymer is essentially a solvation process: gases dissolve in the polymer, diffuse through its bulk, and evaporate from the other side. Fick's law describes an idealized system where solutes don't interact: the amount of CO2 in the tube has no effect on the diffusion rate of O2 into it. I think there's a colorable argument to be made that the system will be non-Fickian.

 

[segallis]

Google "partial pressure."


It's true that people have been enjoying beer for thousands of years, but people have also been putting up with flat oxidized beer for most of that time.

Hmmm, what I see are statements that "partial pressure" describes the contributions of individual gas components on the combined pressure of a mixed gas (usually relating the two for a specific absolute pressure). I don't see any formula (or experiment) that demonstrate this given a continually supplied pressure difference (other than blanket statements to that effect on forums). All the supported arguments I can find having to do with O2 intrusion include things about permeability and diffusion. The mixing of a specific gas from higher concentrations to lower concentrations is explained by the free, unhindered motion of gas molecules and the large space between gas molecules which is also why different gas mix. I also see articles demonstrating that absolute pressure differences affects (and can overcome) much of this interaction.

I would not necessarily equate flat beer to oxidized beer. While I'm sure many would prefer their own homebrew to the cask ales of a century ago, some of the best beers I have had, as well some of the most expensive and most in demand beers I have seen professionally offered, are modern barrel aged ales (which likely introduces a billion times more risk for oxidation than the things discussed on these threads). I'm curious how this part of the industry is enjoying so much success and growth to where they can't age enough B.A. Quads and Wee Heavys, meanwhile a few ppb of O2 are destroying so many homebrews?

 

[Biggz1313]

Hmmm, what I see are statements that "partial pressure" describes the contributions of individual gas components on the combined pressure of a mixed gas (usually relating the two for a specific absolute pressure). I don't see any formula (or experiment) that demonstrate this given a continually supplied pressure difference (other than blanket statements to that effect on forums). All the supported arguments I can find having to do with O2 intrusion include things about permeability and diffusion. The mixing of a specific gas from higher concentrations to lower concentrations is explained by the free, unhindered motion of gas molecules and the large space between gas molecules which is also why different gas mix. I also see articles demonstrating that absolute pressure differences affects (and can overcome) much of this interaction.

I would not necessarily equate flat beer to oxidized beer. While I'm sure many would prefer their own homebrew to the cask ales of a century ago, some of the best beers I have had, as well some of the most expensive and most in demand beers I have seen professionally offered, are modern barrel aged ales (which likely introduces a billion times more risk for oxidation than the things discussed on these threads). I'm curious how this part of the industry is enjoying so much success and growth to where they can't age enough B.A. Quads and Wee Heavys, meanwhile a few ppb of O2 are destroying so many homebrews?

I agree and think you're correct that there is a much higher chance and amount of oxidation happening to these BA beers, but I think the styles that are typically BA and the flavors the BA impart on the finished project are going to be much stronger then the sort of flavors a limited amount of oxidation will bring to those particular beers. This is just me implying some reasoning in my own mind and is basically my opinion so there is no research (that I'm aware of) to back this up, but to me it makes sense.

 

[segallis]

The counter-intuitive case you're proposing is that diffusion into a tube increases its pressure. In most cases this won't happen, because other gases will be diffusing out at the same time. In the extreme cases (say, helium through a glass tube), it does indeed happen, but to say that things get counter-intuitive in extreme cases doesn't refute the underlying principles.

If O2 diffuses into a pressurized CO2 line, then it would seem the same could be said for fermentation purging of a keg over time. Wouldn't O2 permeate through the blowoff water and tube walls and then along that open channel inside the tube back into the keg, so that the keg is being continually replished with more O2 since there wasn't enough in there compared to the surrounding air???

I can see where O2 can intrude (through the water and tube wall) once CO2 is no longer being produced, but it seems that the steady production of CO2 during fermentation is what keeps the O2 out. If I am missing something then please explain how this purging removes and then keeps O2 out, while a CO2 bottle can't?

I can undertand that the number of mols of different gasses on two different sides of a hose can be rearranged such that the partial pressures on boths sides are at equillibrium, and the aboslute pressures maintain the same different numbers you started with. But I don't underatnd what force casues those molecules of O2, for example, to diffuse throught that hose when there is higher pressure on the other side?

The no membrane case is explained by the rapid and unobstructed motion of gas molecules (i.e. mixing). And the case of a ballon deflating over time explains how molecules of a gas want to move in one direction through a membrane from a higher pressure to a lower pressure (rather than just the exchange of dissimilar molecules).

But what force physically moves molecules of a gas from low pressure, through a membrane into a high pressure area???

 

[Broken Crow]

If O2 diffuses into a pressurized CO2 line, then it would seem the same could be said for fermentation purging of a keg over time. Wouldn't O2 permeate through the blowoff water and tube walls and then along that open channel inside the tube back into the keg, so that the keg is being continually replished with more O2 since there wasn't enough in there compared to the surrounding air???

I can see where O2 can intrude (through the water and tube wall) once CO2 is no longer being produced, but it seems that the steady production of CO2 during fermentation is what keeps the O2 out. If I am missing something then please explain how this purging removes and then keeps O2 out, while a CO2 bottle can't?

I can undertand that the number of mols of different gasses on two different sides of a hose can be rearranged such that the partial pressures on boths sides are at equillibrium, and the aboslute pressures maintain the same different numbers you started with. But I don't underatnd what force casues those molecules of O2, for example, to diffuse throught that hose when there is higher pressure on the other side?

The no membrane case is explained by the rapid and unobstructed motion of gas molecules (i.e. mixing). And the case of a ballon deflating over time explains how molecules of a gas want to move in one direction through a membrane from a higher pressure to a lower pressure (rather than just the exchange of dissimilar molecules).

But what force physically moves molecules of a gas from low pressure, through a membrane into a high pressure area???

...it's the O2 Gnomes... They delight in mining through barely porous material carrying oxygen and dumping in the brews of the O2CD brewers on here.

 

[tracer bullet]

Hmmm, what I see are statements that "partial pressure" describes the contributions of individual gas components on the combined pressure of a mixed gas (usually relating the two for a specific absolute pressure). I don't see any formula (or experiment) that demonstrate this given a continually supplied pressure difference (other than blanket statements to that effect on forums). All the supported arguments I can find having to do with O2 intrusion include things about permeability and diffusion. The mixing of a specific gas from higher concentrations to lower concentrations is explained by the free, unhindered motion of gas molecules and the large space between gas molecules which is also why different gas mix. I also see articles demonstrating that absolute pressure differences affects (and can overcome) much of this interaction.

I would not necessarily equate flat beer to oxidized beer. While I'm sure many would prefer their own homebrew to the cask ales of a century ago, some of the best beers I have had, as well some of the most expensive and most in demand beers I have seen professionally offered, are modern barrel aged ales (which likely introduces a billion times more risk for oxidation than the things discussed on these threads). I'm curious how this part of the industry is enjoying so much success and growth to where they can't age enough B.A. Quads and Wee Heavys, meanwhile a few ppb of O2 are destroying so many homebrews?

You aren't wrong about the general definition of partial pressure. It's not the "one thing" to point at for all of the explanation. The gist is that the partial pressure of the gasses on each side of a barrier will want to be equal. The partial pressure of O2 on the outside of the line will want to try to enter the inside of the line until they are equal (regardless of what other gasses are on each side, or their pressures). So partial pressure is sort of the reason but you can't just go search for the definition and get the whole explanation being looked for.

Your 2nd half I'm not sure what to say, it's a bit of a strawman. O2 gets into beers and oxidizes them. It's up to the person, particularly with the beer type, to decide if they care. A homebrewer that transfers a hazy IPA into a keg through a tube with a lot of splashing will have crappy beer that lost its intended hop flavors in a matter of just days. Minimizing O2 ingress keeps things better, longer. At some point it gets to be a silly chase, but keeping out O2 makes a difference. I'd hope you agree, if not then you'd be welcome to make a hazy IPA and see how much O2 you can introduce and how it tastes afterwards.

If you can agree that a beer can be oxidized, and change flavor (better or worse is in the eye of the beholder), then I'd think you can start to see why some people care for some beers and go through the work. to minimize it, for certain beer types where they want a particular outcome (hazy NEIPA that they want to keep the smell and flavor around on day 30 like it was on day 1).

Some people conversely "age" beer, i.e. their Imperial Stouts and it could be that they are simply preferring some oxidation. I've always thought this to be the case, actually, that we prefer these beers to be oxidized. Flavors may not "mellow" or hops" smooth out" in these beers, maybe they simply oxidize away, or at least change, in a way we believe is better. So you can't put a blanket statement on oxidation, or say that... since it's OK for an aged quad that it must therefore be OK for a hazy IPA. Apples to oranges comparison. Or quads to hazies comparison.

If O2 diffuses into a pressurized CO2 line, then it would seem the same could be said for fermentation purging of a keg over time. Wouldn't O2 permeate through the blowoff water and tube walls and then along that open channel inside the tube back into the keg, so that the keg is being continually replished with more O2 since there wasn't enough in there compared to the surrounding air???

I can see where O2 can intrude (through the water and tube wall) once CO2 is no longer being produced, but it seems that the steady production of CO2 during fermentation is what keeps the O2 out. If I am missing something then please explain how this purging removes and then keeps O2 out, while a CO2 bottle can't?

I can undertand that the number of mols of different gasses on two different sides of a hose can be rearranged such that the partial pressures on boths sides are at equillibrium, and the aboslute pressures maintain the same different numbers you started with. But I don't underatnd what force casues those molecules of O2, for example, to diffuse throught that hose when there is higher pressure on the other side?

The no membrane case is explained by the rapid and unobstructed motion of gas molecules (i.e. mixing). And the case of a ballon deflating over time explains how molecules of a gas want to move in one direction through a membrane from a higher pressure to a lower pressure (rather than just the exchange of dissimilar molecules).

But what force physically moves molecules of a gas from low pressure, through a membrane into a high pressure area???

If you have a silicone blow-off tube, it absolutely will allow O2 into your fermenter. Not sure about how fast it'll come through a liquid, but yes, it will come through there as well. O2 will get into the water you have your blow-off tube inserted into and it will come out the other side in the blow-off tube that way as well (unless of course it's already become equal in partial pressure inside the fermenter and out but this would take a long while). I can't say how fast, or if anyone should care, but yes it happens.

CO2 generation in the fermenter will of course be blown out, but it doesn't keep the O2 from coming in at the same time. Some O2 will get carried out by the CO2 of course, but it will continue to come in 24/7/365 regardless. As fermentation slows, it'll stay in the fermenter longer.

No idea what you are asking about purging and CO2 bottles.

Diffusion of O2 into a beer line that it can permeate through is a counter intuitive thing but it does do it. And YES it can raise the pressure inside the line, all else being equal. It's probably in real life balanced by the CO2 escaping from the line, or being absorbed into the beer, and things like that. But it doesn't HAVE to be balanced by CO2 removal. O2 will still permeate through, and even if the existing CO2 in the line doesn't go anywhere, it'll come in, and it'll raise the overall pressure in the line. The fact that the CO2 pressure is higher inside than the "air" pressure outside is not enough to prevent this permeation. O2 partial pressure in the air will find its way to having a similar O2 partial pressure inside the line, even if the line has a higher "overall" pressure. This is where partial pressure comes into play again. That O2 doesn't care what's already there, it's coming anyhow, like it or not.

 

[mac_1103]

But what force physically moves molecules of a gas from low pressure, through a membrane into a high pressure area???

The concentration gradient of that specific gas across that membrane. You wouldn't be able to breathe if it didn't work this way.

 

[AlexKay]

It certainly won't hurt to use EVABarrier for the blowoff tube, for connecting kegs to the fermenter for purging, and everything else. As with anything else, it's a matter of degree -- EVA is still permeable, but it's substantially better than PVC (and let's not talk about silicone.)

As far as oxygen making it through the airlock, you will absolutely have 9 ppm of O2(aq) in the airlock/blow-off-tube water. It's a relatively slow process to equilibrate with O2(g), though. Eventually, you'll equilibrate to the same gas composition on both sides of an airlock, despite the presence of the water, but I suspect this takes a very long time.

Also, there's a significant distinction to be made between diffusion through a permeable material and diffusion of one gas through another. The latter process is quite slow (root time) in the absence of convection (free or forced).

Give or take a factor of 2, professionals target ~100 ppb O2(aq) as total package oxygen -- dissolved, headspace, everything. That's achievable in home brewing, though not without going to some trouble. Targeting <10 ppb probably isn't, and the folks who think they're getting there are probably missing some avenues of ingress.

 

[segallis]

The concentration gradient of that specific gas across that membrane. You wouldn't be able to breathe if it didn't work this way.

Not to go too far down a bunny trail, but the exchange of gases inside the lungs is a gas-to-liquid transfer across a membrane, and does not involve much pressure difference (the pressure difference existes to move air in and out of the lungs). If anything there would be higher pressure in the inhaled air tending to move gas into the avioli when you inhale, and then lower pressure on the air side of the membranes when you exhale tending to move CO2 out. The differing solubility for various gases in these tissues is also a factor.

Regardless, "concentration gradient" is not a cause - it is an effect. Take a container divided into two halves, O2 on one side, CO2 on the other. Now remove the divider. Sure there is a concentration (partial pressure) difference. The gases will mix and the partial pressures will equalize on both sides over time. That is a an EFFECT. The cause for that mixing and equalizing of partial pressures is the fact that the gas molecules are in constant and unobstructed motion. The fact that the concentration equalizes is a simple consequence of statistical motion. O2 molecules from the right side are moving in all directions, so some move to the left side. Once there is 10% concentration on the left side, there will be 1/10 as many molecules moving back towards the right side as are moving to the left. Eventually the gases are completely mixed and there are as many O2 molecules moving from the right side to the left side as from the left side to the right. Simple statistical probability results in equal concentrations. But the concentration has ZERO to do with why that condition is eventually established. The "effect" of equal concentrations is "caused" by the random motion of the gas molecules.

Attributing the final effect of equalizing gases on two sides of a barrier to "gases want to be the same everywhere" is popular, but cannot be explained with facts. (Sort of like people asserting that a plane can fly due to the airfoil shape of a wing). The gas on the outside of a hose isn't "motivated" to get to the other side because there are fewer molecules of that type inside the hose - it is simply random motion and statistics.

Anything that impedes or prevents (e.g. a barrier) that motion of molecules will impede or prevent the equalization of concentrations (partial pressures). At zero pressure difference, diffusion is unimpeded and we see mixing of gases in relatively little time. Add a barrier and the effect is slowed. Random motion of a gas molecule will cause some to penetrate the surface of a hose. Random motion will cause it move in various directions, some of which will exit the hose material on the other side. Again - random motion is the cause. But it is obvious that there are things that can impede or prevent that random motion across certain barriers (e.g. EVA). The question is whether pressure can do so?

Which brings me back to the example of a latex balloon. The balloon will deflate over time - regardless of what the gas concentrations are inside vs outside the balloon. And for one simple reason: the higher pressure inside the balloon results in gas molecules moving through the membrane in (nearly) one direction. If molecules were traveling in both directions in equal number, the balloon would never deflate.

If this can't be explained, then dismissing the effect of pressure appears to be without basis.

 

[tracer bullet]

Not to go too far down a bunny trail, but ... Attributing the final effect of equalizing gases on two sides of a barrier to "gases want to be the same everywhere" is popular, but cannot be explained with facts. (Sort of like people asserting that a plane can fly due to the airfoil shape of a wing). The gas on the outside of a hose isn't "motivated" to get to the other side because there are fewer molecules of that type inside the hose - it is simply random motion and statistics.

Well, there's always the possibility you can't believe something that's actually true and just don't really know you're talking about.

 

[segallis]

Well, there's always the possibility you can't believe something that's actually true and just don't really know you're talking about.

Or the possibility that some are believing something that isn't true and regurgitating it with nothing to prove it. A law of physics is explained with facts and backed by empirical evidence - as opposed to, say, an old wives tale.

What specifically did I say that is not true? Show me a balloon that stays inflated. Explain why it deflates if the number of molecules through the membrane are equal in both directions? Please show me why you know what you're talking about - I'm always open to learn truth. If you are going insult me, then at least offer a fact or two to support your opinion, or answer one of these questions I have asked.

And for the record, it is proven fact that the mixing of gases is the result of random molecular movement (which was my claim regarding cause). The laws of thermodynamics and entropy are also well proven and demonstrable. Just as it can be shown that areas of high pressures will flow to lower pressures (i.e. the movement of molecules).

"If a man has the correct answer but he has no idea why, is he really right?"

 

[tracer bullet]

What specifically did I say that is not true?

That partial pressure is a fairy tale and that wings don't keep planes in the air.

Everything you need to know about O2 getting into your beer lines is available to you, the onus is not on me nor anyone else to paraphrase it and prove it, or to refute your oddities one at a time when you make 10 at once.

I'm done here, by the way. Not because you're right, but because I've learned over the decades some people will never be convinced and it's not worth the time to try. If O2 doesn't get into your silicone lines, that's awesome. Keep using them. I'm 100% fine with it.

 

[AlexKay]

Which brings me back to the example of a latex balloon. The balloon will deflate over time - regardless of what the gas concentrations are inside vs outside the balloon. And for one simple reason: the higher pressure inside the balloon results in gas molecules moving through the membrane in (nearly) one direction. If molecules were traveling in both directions in equal number, the balloon would never deflate.

This is technically an "argument from incredulity" -- in your experience, balloons have always deflated; therefore, they must never inflate. However, your experience is only with balloons in an air environment, filled with either air or helium (or, if you live interestingly, hydrogen.) In the case of air, partial pressure gradients all point towards the outside of the balloon, and for helium, the permeability of the latex to helium is much larger than it is to air, so helium loss will be (much) faster than air ingress.

If you had an air-filled balloon (or one filled with a gas with even lower permeability; xenon, say, or SF6) in a helium environment, you would indeed see an initial increase in pressure of the balloon. It seems hard to believe, but that is because you do not live with a helium atmosphere.

 

[segallis]

That partial pressure is a fairy tale and that wings don't keep planes in the air.

Everything you need to know about O2 getting into your beer lines is available to you, the onus is not on me nor anyone else to paraphrase it and prove it, or to refute your oddities one at a time when you make 10 at once.

I'm done here, by the way. Not because you're right, but because I've learned over the decades some people will never be convinced and it's not worth the time to try. If O2 doesn't get into your silicone lines, that's awesome. Keep using them. I'm 100% fine with it.

Hmmm, I'll type slower this time...

• What fairy tale? I cited the actual definition of partial pressure. And that the partial pressure in a mixture results from random movement of molecules.
• The primary factor that enables a plane to fly is the angle of attack of the wing, rather than its shape (as is proven by inverted flight, as well as flat wing gliders) Although that was more of satire, not me looking for you to refute it, LOL
• 10? I beleive I boiled it down to two simple questions: 1) A balloon will deflate 2) Partial pressures are the result of random molecular movement (sorry that those two were so overwhelming) I view those more as "observable facts" than "oddities".

I can be convinced of many things, if backed by truth and facts. It is why I have been extremely sucessful as engineer for 40 years now.
I stated several scientific facts and empirical evidence and asked for something - other than unsubstantiated opinion - to support or refute that. You offered no facts, experiments or even substantiated theory. You didn;t even quote my claim accurately.

So on one thing we agree - you watsed your time (and mine).

 

[segallis]

This is technically an "argument from incredulity" -- in your experience, balloons have always deflated; therefore, they must never inflate. However, your experience is only with balloons in an air environment, filled with either air or helium (or, if you live interestingly, hydrogen.) In the case of air, partial pressure gradients all point towards the outside of the balloon, and for helium, the permeability of the latex to helium is much larger than it is to air, so helium loss will be (much) faster than air ingress.

If you had an air-filled balloon (or one filled with a gas with even lower permeability; xenon, say, or SF6) in a helium environment, you would indeed see an initial increase in pressure of the balloon. It seems hard to believe, but that is because you do not live with a helium atmosphere.

I was actually thinking of a balloon filled with air or CO2. A balloon filled wth CO2, will experience a positive partial presssure for Nitrogen (as one component) from the outside, i.e. a gradient pointed inward. So Nitrogen would tend to permeate into the balloon due to random motion (the random motion on the other side is 0, since there is no Nitrogen inside the balloon).
The baloon is more permeable to Nitrogen penetrating in, than CO2 escaping out.
The balloon will still deflate.
For the balloon to remain inflated, the number of mols of CO2 escaping would need to be equal to the total number of mols of other gases present in air (which all have a higher partial pressure outside the balloon).

The fact that the baloon deflates proves that more CO2 molecules have escaped than other gases combined have penetrated. Which means there is net movement of molecules out of the balloon due to the internal pressure. (I never claimed zero molecular penetration, just a bias outward resulting from pressure. The higher the pressure, the greater the bias). If the balloon is supplied by a continuous source of CO2 maintaining that internal pressure, the balloon will remain inflated and the the bias will remain - as will the imbalance of gas partial pressures on both side of the balloon.

Compare that to a case where the balloon is stretched as a divider in a tank, with air on one side and CO2 on the other. Over time, the partial pressures will equalize and remain at equilibrium because there is identical statistical probability for any partiular gas molecule to travel in either direction through that barrier (even though diffferent gases may have different probability compared to Nitrogen, or Helium, for example, due to permeability of the barrier). Meaning molecules of Nitrogen will be equally likely to pass in either direction, which why the partial pressure of Nitrogen will remain equal on both sides.

 

[segallis]

If you had an air-filled balloon (or one filled with a gas with even lower permeability; xenon, say, or SF6) in a helium environment, you would indeed see an initial increase in pressure of the balloon. It seems hard to believe, but that is because you do not live with a helium atmosphere.

Now this is something I can try. If I take a latex balloon and put it inside a mylar balloon, then fill the latex ballon with air and seal it. Then fill the mylar balloon with helium. You're saying I will see the latex ballon expand - or at least not deflate? Or possibly deflate slower than if I leave the latex balloon in ambient air (and assuming I only fill the helium mylar baloon to atmospheric pressure to keep relative pressures the same for both cases)?

 

[AlexKay]

Now this is something I can try. If I take a latex balloon and put it inside a mylar balloon, then fill the latex ballon with air and seal it. Then fill the mylar balloon with helium. You're saying I will see the latex ballon expand - or at least not deflate? Or possibly deflate slower than if I leave the latex balloon in ambient air (and assuming I only fill the helium mylar baloon to atmospheric pressure to keep relative pressures the same for both cases)?

I agree with this proposed experiment in principle: I would expect the balloon-in-the-balloon to inflate first as helium permeated inwards. No idea whether the effect will be large enough to be apparent to the eye.

 

[segallis]

Finally, some science to prove I am wrong... and right And the answer is:
A keg that is left at ambient pressure and has a hose or gasket that is permeable to air, will EVENTUALLY* contain 21% oxygen inside.

A keg that is pressurized and maintained to 15 psi with a continuous supply of CO2, will EVENTUALLY* contain 10.5% oxygen inside (and at 40 psi, the O2 level would equalize to 7.8%)

I am offering up a reward of my treasured Apple Brandy Aged Gulden Draak, Ommegang 20th Anniversary Bourbon Barrel Aged Belgian Strong Ale, and 2018 Thomas Hardy's Ale 50th Anniversary Golden Edition to anyone that can disprove the gist of the claims in this post

Out of a desire to know the facts, I dug deeper into the science and then simulated gas behavior under varying conditions. In case anyone is interested in discerning truth vs. partial-truth vs. misinformation, I am posting the painfully lengthy results of this effort.

I talked with a friend who is a physicist and he clarified some things and verified some things, which inspired me to model the scenarios discussed. Using the proven laws of physics, (Boyle's, Dalton's, Avogadro's, Amonton's, Charles', Graham's, kinetic molecular laws, laws of thermodynamics, laws of motion), I generated several Matlab models to simulate different scenarios. These simulations are in agreement with the laws mentioned, and they shed light on the fundamental truths that are the CAUSES of the numerous resulting EFFECTS that we observe.

A couple of notes regarding my simulations. They assume a constant temperature for the entire system. I also plugged in an arbitrary rate of permeability across the membrane, which only affects the time period in actual time and simulation iterations required to achieve the outcome, but has no impact on the final results in terms of moles, absolute and partial pressures, concentrations, equilibrium, etc. I simplified ambient air to 79% nitrogen, 21% oxygen and 0% CO2. I also factored in differing rates of permeability using Graham's law, so that O2 permeates 1.17X faster than CO2 and Nitrogen permeates 1.25X faster than CO2 (according to their molecular weight, i.e. density). I assumed uniform dispersion/mixing of gases relative to the time required for diffusion.

Here are the summary results of these laws and simulations, as well as corollaries derived from the facts, and clarification for some of the popular myths being propagated. I welcome any counter-proof to anything I have stated.

The cited laws (not me) establish that the kinetic energy of every gas molecule is proportional to its temperature. For a given temperature... Lighter gas molecules have the same KE as heavier gas molecules. KE=1/2mv^2, therefore, heavier gas molecules move slower than lighter molecules. Pressure does not affect the KE of a particular gas molecule. Pressure does affect the rate at which gas molecules will strike a barrier, since there are more molecules per unit volume at higher pressure.

The motion of gas molecules is random motion due to kinetic energy. Diffusion through a permeable membrane results from this random motion, and the rate of diffusion through it is dependent on the probability of a gas molecule colliding with the membrane. So, more moles per unit volume will result in more diffusion through a membrane. This fundamental truth explains everything else.

Please read this point to the end: The motion of gas molecules, as well as the probability of collision with the membrane is unaffected by anything on the other side of that membrane. Meaning, the rate at which gas molecules diffuse FROM LEFT TO RIGHT through a membrane has NOTHING to do with the concentration/partial pressure of that gas on the other side. It is totally dependent on the number of moles of that gas on the left side of membrane. Same goes for the right side. The EFFECT of that fact is that a higher concentration of a particular gas on the left side will result in more molecules of that gas diffusing from left to right than in from right to left. Eventually the concentration will build up on the right side until equilibrium is reached, and the diffusion of molecules is the same in both directions. But this equilibrium doesn't cause this diffusion to cease in either direction, it merely becomes the same number in both directions. There will always be molecules of that gas moving from left to right and right to left at a rate dependent only on the number of molecules on the respective side.

There is no motivating force to drive oxygen molecules from one side to the other because of any concentration imbalance. It is simply kinetic energy and random probability that moves the molecules. If there is 21% oxygen present on the left side, the number of moles of O2 per unit time diffusing FROM LEFT TO RIGHT will be the same number whether there is zero O2 on the other side, or 99% O2 on the other side. Same goes for the right side, so the EFFECT will be a NET DIFFERENCE in diffusion that is solely dependent on the difference between the number of moles of O2 on the left vs the right. So for the case of ambient air on the left of the membrane (where O2 remains at 21%), the number of moles of O2 per unit time diffusing LEFT-TO-RIGHT will be constant regardless of the O2 concentration/partial pressure/build-up on the other side. As O2 builds up on the right side, the number of moles diffusing right-to-left increases and only the NET difference in molecules moving through the membrane will diminish.

Eventually there will be the same number of moles of O2 on both sides of the membrane, and things remain at equilibrium since the same number of molecules will be moving from the left side to the right as in the opposite direction. (The net will be zero but the number of molecules crossing the membrane in either direction will still be a function only of the total number of moles on either side).

Further, while the NUMBER OF MOLES OF O2 will eventually equalize to the same number on both sides, this does not require that the concentration must be equal on both sides. O2 concentration will be equal on both sides only if the absolute pressure is the same on both sides. But if the the absolute pressure on the right side happens to be higher than the left, that equilibrium point of the same number of moles of O2 on both sides will actually result in a lower concentration of oxygen on the right side. This example case can exist if the right side pressure is maintained with a regulator and a continuous source of CO2. I am providing a simulation for this case that demonstrates a lower concentration of O2 on the right side of the membrane (due to higher absolute pressure), while the diffusion of O2 molecules is across the membrane is equal in both directions (i.e. equilibrium, since the number of O2 moles is equal on both sides).

My simulations also include the case of a balloon, where the balloon is filled with CO2 to varying pressure levels. These balloon simulations all show the balloon pressure eventually approaching ambient (i.e. deflating). The sims also demonstrate the case where the balloon pressure can actually increase for a time - which was enlightening to me. This case can occur due to differences in the rate of permeability for the different gases. In this simulation, Nitrogen and Oxygen start to enter the balloon faster than CO2 can permeate out, and the pressure increases until the build up of O2 and N2 inside the balloon begin to lower the net diffusion of those gases to the point they equal the rate of CO2 diffusion out. After that point the rate of CO2 diffusion outward dominates and the pressure inside the balloon begins to drop until it reaches ambient, at which point the gas in the "deflated" balloon is the same 79%/21%/0% N2/O2/CO2 mix as in the ambient air. Also, the initial pressure increase into the balloon will NOT occur if the starting CO2 pressure inside the balloon is high enough such that the increased number of CO2 molecules inside the balloon results in more CO2 molecules permeating out than O2 and N2 permeating in (despite the higher rate of permeability for N2 and O2 compared to CO2). This will be the case if the CO2 balloon initial pressure is anything above 1.2332 ATM. At anything above 1.23 ATM, there will always be a NET movement of gas molecules out of the balloon and pressure will always drop (even though O2 and N2 are still permeating into the balloon).

The other simulations model the case where the enclosed volume is maintained at a constant pressure with a continuous supply of CO2 gas - which is the example of a keg fed with a CO2 bottle. These simulations clearly show that, while my rationale for the forces that cause these gas molecules to move and diffuse was accurate, my theory about the final effect was in error. The fact is that O2 will tend to diffuse into the higher pressure CO2 line until the number of O2 molecules per unit volume is equal on both sides. The result is that the O2 concentration will be lower than for ambient air if the regulator pressure is higher than ambient. Again, the number of moles of O2 will equalize on both sides, regardless of regulator pressure. As the regulator pressure is close to ambient that equal number of moles will cause a similar concentration, but as the regulator pressure is increased, that same number of moles results in lower concentration, albeit, still a significant percentage since practical regulator pressure is only 1.5X to 2X that of ambient, so maybe 10.5 to 14% O2 concentration at equilibrium.

------------------------------------

The simulations show the eventual conditions of equilibrium given enough time. The missing piece is relating those simulation curves to an actual timeline in terms of days and hours, since I don't have actual permeability numbers for a PVC hose, o-rings etc. The impurity of the CO2 source is also a real-world factor. And the ultimate question is how much of that O2 is actually get dissolved into the beer over the normal time and drain rate of a typical keg (my friends have managed to help empty my last 4 kegs with 1 week of putting them on CO2. I blame the NFL.)

Which is why I intend to do an experiment: fill two kegs 1/2 way with enough sugar water and yeast to yield a relatively oxygen free starting point. Keep both kegs connected to PVC CO2 lines - one without supplying any new CO2 to the line, the other supplying 15 psi CO2 over ambient. Allow both kegs to sit like this for maybe 2 months. Take samples from each (maybe 4 to 8 tests over the 2 month period) and use a Winkler/LaMotte dissolved oxygen test kit to measure dissolved oxygen. This should reveal how far along the theoretical O2 intrusion curve things progress over a typical time period and keg volume. It would probably be beneficial to have a 3rd keg and do a shake under pressure to force carbonate quickly and do a D.O test to establish the purity of the CO2 source to begin with (possibly that can be deduced form the other two test cases?)

Any advice on whether I should buy a test kit with a resolution of ppb or ppm???

 

[AlexKay]

Kudos for all the work!

Just checking in on a matter of definitions. Partial pressure is just that, a pressure, but not a proportion. So air has an O2 partial pressure of ~210 mbar, as it is composed of 79% nitrogen/21% oxygen. If you use a regulator and a tank of CO2 and bump the total pressure to 3 bar, the proportion of O2 in the mixture goes down, but the partial pressure is still 210 mbar.

Note also that in most cases a polymer will be more permeable to CO2 than O2, because the former is more soluble in the material. This is why I was proposing experiments with helium.

 

[segallis]

Kudos for all the work!

Just checking in on a matter of definitions. Partial pressure is just that, a pressure, but not a proportion. So air has an O2 partial pressure of ~210 mbar, as it is composed of 79% nitrogen/21% oxygen. If you use a regulator and a tank of CO2 and bump the total pressure to 3 bar, the proportion of O2 in the mixture goes down, but the partial pressure is still 210 mbar.

Note also that in most cases a polymer will be more permeable to CO2 than O2, because the former is more soluble in the material. This is why I was proposing experiments with helium.

Ya, I got carried away with my slashes, including partial pressure in a few places I should have omitted it.

So that raises an interesting point. Take the example of a CO2 supply regulated at 15 psi over ambient. Even though the equalized O2 concentration is half that (10.5%) of ambient air, since the partial pressure is the same, the beer ought to oxidize at the same rate, since O2 will dissolve into the beer at the same rate, right?

 

[AlexKay]

So that raises an interesting point. Take the example of a CO2 supply regulated at 15 psi over ambient. Even though the equalized O2 concentration is half that (10.5%) of ambient air, since the partial pressure is the same, the beer ought to oxidize at the same rate, since O2 will dissolve into the beer at the same rate, right?

That would be my thinking, yes.

I had the interesting thought that if you were supplying CO2 to a regulated pressure, and you had a leak in your system, then depending on the relative speed of oxygen permeation in and gas (CO2 and oxygen, both) leaking out, you could end up with very little oxygen in your lines, steady-state. And I suspect that with hose barbs and PVC tubing, you nearly always have some kind of leak. Hm.

 

[segallis]

I do enjoy an exercise like this, and really plan to do the 2 keg experiment, measuring dissolved O2. But I do all this only for the challenge and to have accurate data. Truth is, I have very little concern about oxidation (due to hoses, o-rings ) being a significant factor in my beer enjoyment, though I am careful during handling/transfers. I say that for several non-scientific reasons...

1) I always bottle 8 pints or so along with 2 kegs. The bottles are naturally carbonated, so likely, MUCH lower O2 exposure/infiltration than my kegs see, which often times are filled without purging, and are typically force carbonated with "impure" CO2, and then sit vulnerable to O2 storm troopers via the 3 foot PVC CO2 hoses during their ~ 4 week lifespan on tap (possibly as little as 1 week, but if God is smiling on me, maybe as long as 8 weeks). I really don't notice any detectable difference in the quality of my "pure" bottle vs my "contaminated" kegs.

2) In my last 200 visits to microbreweries I have always opted for their barrel-aged versions when available and have not been disappointed.

But all this shared obsession is not in vain, I have seen the light and plan to purge my kegs from now on, and will probably naturally carbonate - OK, I'm probably only doing that part to save on paying for CO2, rather than out of a fear of using welding CO2.

 

[AlexKay]

I always figured that there were reasonable measures to take (pouring without splashing, purging headspace, not using PVC) and unreasonable measures (purging kegs with fermentation gas, closed transfers), and that the unreasonable measures might make sense if you were making NEIPA, but not really any other time. In support of this, I always liked the way my beer turned out, including hoppy beers like APAs.

As this thread has been playing out, I made my first beer (a black IPA) using all the unreasonable measures, too … and you know, they’re suddenly seeming not so unreasonable. I’m blown away, not just by how much hop flavor there is, but how much malt flavor there is alongside it.

So I’ve ordered another spunding valve, set aside some kegs to ferment in, and am going to go all out keeping cold-side oxygen out of everything I make. If it turns out not to make so much difference, I’ll go back to the easier way of doing things.

 

[Bobby_M]

Which brings me back to the example of a latex balloon. .... If molecules were traveling in both directions in equal number, the balloon would never deflate.

Maybe I'm committing a common sense fallacy here but are you overlooking that a latex balloon has elasticity and is being stretched when full?