CO2 blanket poll

[Clyde McCoy]

I did read through all of the replies, but I will point out that open bucket fermentation is real. In a room withoit air movement and while fermentation is active, there is absolutely a blanket of CO2. As activity slows, the it gets thinner but as long as it is being produced, the layer exists. Once it stops, air will mix in but the impact is negligible. Only if you disturb the wort by adding dry hops or stirring will oxidation become a problem. That said - closed transfers and oxygen exclusion when handling beer is critical.

Just wondering, are you brewing in a room at zero kelvin?

 

[BrewnWKopperKat]

Re: "In another thread it was shown by at least three homebrewers that filling the neck of the bottle with CO2 results in a much less oxydized beer, a beer which is very easily distinguishable either visually or in the taste test."

Focusing on the bottling technique (not the engineering or science that may be involved), it appears that the technique was effective - it was able to keep beer in bottles longer.

There appear to be other approaches to bottling beer that involve minimizing the effects of oxygen ingress.

Discussing science can be interesting.

Pragmatic approaches to minimizing the effects of oxygen ingress can be useful.

 

[Clyde McCoy]

This is another thread I have to mark as ignore. Happy brewing everyone!

Big +1, onto better things!

 

[jerrylotto]

Once fermentation stops the blanket is over

Not if the room is closed and there are a lot of buckets....

 

[Vale71]

I did read through all of the replies, but I will point out that open bucket fermentation is real. In a room withoit air movement and while fermentation is active, there is absolutely a blanket of CO2. As activity slows, the it gets thinner but as long as it is being produced, the layer exists. Once it stops, air will mix in but the impact is negligible. Only if you disturb the wort by adding dry hops or stirring will oxidation become a problem. That said - closed transfers and oxygen exclusion when handling beer is critical.

That layer is very visible and it's commonly referred to as Kräusen. It's not an "invisible layer of gas" but as a matter of fact it's a very visible layer of (CO2 filled) foam and trub and yeast. That is the (very visible) layer that is protecting the beer from oxygen ingress. The Kräusen itself is very exposed to oxidation as proven by the outermost layer turning darker or even black. Those are hop resins oxidizing as they are exposed to atmospheric oxygen since there is no "invisible blanket" of CO2 to protect the outer layer. If you remove the Kräusen or let it fall back into the beer at the end of fermentation the beer will be immediately exposed to oxidation, which is why in commercial open fermentations the beer is transferred to closed and purged maturation vessels as final attenuation draws near.

Once fermentation stops the blanket is over

No, once again the blanket was NEVER there (see above).

 

[AMessenger]

Count me in the camp of those who can’t vote because the poll is overly reductive. Yes, CO2 doesn’t provide a perfect barrier, and opening your fermenter introduces some O2, so it is wise to limit how long you have it open, but don’t take the ”gasses mixing“ observation to mean that it is an instantaneous thing and that if you crack the fermenter for a few seconds that you’ve ruined your beer.

There are many factors that go into your final product (ingredient quality, recipe, and all other process details). If your goal is a better hoppy beer be concerned about all factors - obsession over this one factor isn’t the answer.

 

[Dgallo]

That layer is very visible and it's commonly referred to as Kräusen. It's not an "invisible layer of gas" but as a matter of fact it's a very visible layer of (CO2 filled) foam and trub and yeast. That is the (very visible) layer that is protecting the beer from oxygen ingress. The Kräusen itself is very exposed to oxidation as proven by the outermost layer turning darker or even black. Those are hop resins oxidizing as they are exposed to atmospheric oxygen since there is no "invisible blanket" of CO2 to protect the outer layer. If you remove the Kräusen or let it fall back into the beer at the end of fermentation the beer will be immediately exposed to oxidation, which is why in commercial open fermentations the beer is transferred to closed and purged maturation vessels as final attenuation draws near.



No, once again the blanket was NEVER there (see above).

I didn’t realize he said open fermenter. If the lid is closed the co2 will replace the o2 during fermentation

 

[Vale71]

Count me in the camp of those who can’t vote because the poll is overly reductive. Yes, CO2 doesn’t provide a perfect barrier, and opening your fermenter introduces some O2, so it is wise to limit how long you have it open, but don’t take the ”gasses mixing“ observation to mean that it is an instantaneous thing and that if you crack the fermenter for a few seconds that you’ve ruined your beer.

There are many factors that go into you final product (ingredient quality, recipe, and all other process details). If your goal is a better hoppy beer be concerned about all factors - obsession over this one factor isn’t the answer.

You're missing the point here.

Those in the "the CO2 blanket is real!" camp claim that it doesn't matter if opening a vessel will introduce some air (barring complete replacement of CO2 of course) because CO2 will settle in a layer at the bottom of the headspace thus completely preventing contact between beer and the introduced O2.

Those in the "we know how this actually works and are getting tired of trying to explain it to those in the other camp" will explain to you that it doesn't matter whether introduced oxygen will diffuse in a matter of seconds or minutes or even hours (it'a at best minutes by the way). If your beer is going to be sitting in the vessel for weeks or even months it will have full contact with introduced O2 for 99,99% of that time. This in turn means that the only thing that matters is how much O2 is introduced into the vessel during the operation. How quickly you open and close the vessel is completely irrelevant, all the O2 you introduce will contribute to beer staling and that (the total amount of O2) is the only thing you need to worry about. That is, if you choose to worry about it. If as a homebrewer you choose to not care about it that's fine as well, after all you're not getting paid to brew. It's also marginally fine (but a bit sad) if you choose to delude yourself with this CO2 blanket nonsense but please do not try to convince the world that you're right when it's already been fully proven 300 hundred years ago that you couldn't be more wrong.

 

[BrewnWKopperKat]

You're missing the point here.

I thought the point was in the 2nd paragraph:

There are many factors that go into your final product (ingredient quality, recipe, and all other process details). If your goal is a better hoppy beer be concerned about all factors - [...]

As I said earlier

Discussing science can be interesting.

Pragmatic approaches to minimizing the effects of oxygen ingress can be useful.

 

[Birrofilo]

Idk if anyone said instantaneous, maybe I missed that.

There has been plenty of evidence in this thread that shows the diffusion of gases. Under normal temperatures and pressure, these gases will not “settle” and separate again. Again diffusion does not happen immediately but let’s say you open your fermenter and the air that gets in will definitely diffuse within the day. Now the extent of air that got in, is more important. That is because diffusion WILL occur.

I fear you are trying to say unless someone can produce a specific paper that studies a specific interaction, then it can’t be true. However that a falsity in thinking because these are gas laws.

Depends on your math capabilities and understanding here, but here is a formula and chart for diffusion rate of gases

https://www.engineeringtoolbox.com/air-diffusion-coefficient-gas-mixture-temperature-d_2010.html

Yes, some people say that spraying CO2 in the neck of your bottle is useless, it's a myth that you can fill your neck with CO2, because of the laws of gas.

Under normal temperatures and pressure, these gases will not “settle” and separate again.
It is not clear to me if you agree that GPL "settle" initially or not.

Again diffusion does not happen immediately but let’s say you open your fermenter and the air that gets in will definitely diffuse within the day

You see, the "myth" that some people is trying to "burst" is that it makes no sense to inject CO2 inside the fermenter and close it immediately, or to inject CO2 inside your bottle and cap it immediately.

I fear you are trying to say unless someone can produce a specific paper that studies a specific interaction, then it can’t be true. However that [is] a falsity in thinking because these are gas laws.

Somebody said that GPL being a gas cannot form a layer.
Then somebody else admitted GPL will form a layer, but it also will after some while diffuse even though initially it collects on the ground.
The prevailing idea in this discussion, based on "these are gas laws", is that GPL will not collect on the ground.
Once it is shown that GPL does collect on the ground, and creates a hazard, and this is a fact of life, the further assumption is that, because of gas laws, GPL will mix again with air given time.
This might be true, or might be false, I don't know, so I genuinely would like to see some paper stating that. I suspect this doesn't happen at all, but it's a suspect.

The point is that the "general laws of gas", not being valid for GPL in the initial phase, might not be valid for GPL in the subsequent phase! The general law of gas does not explain that GPL collects to the floor and I don't see how could it explain that after that, after a while, GPL will diffuse again. I showed you empirical evidence that GPL does not obey to the laws of perfect gases. You have to show me some empirical evidence that after a while it will diffuse.

My contention is that waving gas laws (ideal-gas laws) doesn't always work because those laws do not apply to all gases and to all circumstances. Some people take them as the Gospel, but they are just instruments in the hand of the wise and knowledgeable physician, with a certain limited scope of validity.

Empirical evidence shows, in the case of beer just like in the case of GPL, that gases do form layers in a way that has an effect (on the beer, on the explosion). I find nonsensical that people uses the equations to deny empirical evidence.

This reminds me of that scene in the Life of Galileo by Brecht (or rectius in one of the versions), when Galileo invites two Dominicans, who said the moons of Jupiter (the "Medicean planets") could not exist, to just look in the telescope and see them with their eyes. The Dominicans reply that science is right and it cannot fail, while senses can fail, therefore even if the planets are visible, they might not be there, but could be the result of an illusion of the senses.

The problem with their reasoning is that they think that their "science" is right regardless of empirical evidence. They think they can be right a priori, because they trust what they call "science", what is written in their "book of absolutely right rules". Science is observation first, hypothesis and modelization after, and empirical demonstration through experiments (cimento) after. In the first and third stage you have the "facts" that you want to explain. You cannot explain regardless of facts!. Those equations have a meaning only insofar as they explain the facts.

The proof is in the beer!

 

[SFC Rudy]

Gases will not mix until to expose them to each other. A sealed fermeter will be full of CO2. When you open it the CO2 and outside gasses will begin to mix.

 

[TheMadKing]

Yes, some people say that spraying CO2 in the neck of your bottle is useless, it's a myth that you can fill your neck with CO2, because of the laws of gas.

Under normal temperatures and pressure, these gases will not “settle” and separate again.
It is not clear to me if you agree that GPL "settle" initially or not.

Again diffusion does not happen immediately but let’s say you open your fermenter and the air that gets in will definitely diffuse within the day

You see, the "myth" that some people is trying to "burst" is that it makes no sense to inject CO2 inside the fermenter and close it immediately, or to inject CO2 inside your bottle and cap it immediately.

I fear you are trying to say unless someone can produce a specific paper that studies a specific interaction, then it can’t be true. However that [is] a falsity in thinking because these are gas laws.

Somebody said that GPL being a gas cannot form a layer.
Then somebody else admitted GPL will form a layer, but it also will after some while diffuse even though initially it collects on the ground.
The prevailing idea in this discussion, based on "these are gas laws", is that GPL will not collect on the ground.
Once it is shown that GPL does collect on the ground, and creates a hazard, and this is a fact of life, the further assumption is that, because of gas laws, GPL will mix again with air given time.
This might be true, or might be false, I don't know, so I genuinely would like to see some paper stating that. I suspect this doesn't happen at all, but it's a suspect.

The point is that the "general laws of gas", not being valid for GPL in the initial phase, might not be valid for GPL in the subsequent phase! The general law of gas does not explain that GPL collects to the floor and I don't see how could it explain that after that, after a while, GPL will diffuse again. I showed you empirical evidence that GPL does not obey to the laws of perfect gases. You have to show me some empirical evidence that after a while it will diffuse.

My contention is that waving gas laws (ideal-gas laws) doesn't always work because those laws do not apply to all gases and to all circumstances. Some people take them as the Gospel, but they are just instruments in the hand of the wise and knowledgeable physician, with a certain limited scope of validity.

Empirical evidence shows, in the case of beer just like in the case of GPL, that gases do form layers in a way that has an effect (on the beer, on the explosion). I find nonsensical that people uses the equations to deny empirical evidence.

This reminds me of that scene in the Life of Galileo by Brecht (or rectius in one of the versions), when Galileo invites two Dominicans, who said the moons of Jupiter (the "Medicean planets") could not exist, to just look in the telescope and see them with their eyes. The Dominicans reply that science is right and it cannot fail, while senses can fail, therefore even if the planets are visible, they might not be there, but could be the result of an illusion of the senses.

The problem with their reasoning is that they think that their "science" is right regardless of empirical evidence. They think they can be right a priori, because they trust what they call "science", what is written in their "book of absolutely right rules". Science is observation first, hypothesis and modelization after, and empirical demonstration through experiments (cimento) after. In the first and third stage you have the "facts" that you want to explain. You cannot explain regardless of facts!. Those equations have a meaning only insofar as they explain the facts.

The proof is in the beer!

You are misinterpreting and misunderstanding your observations, which is the issue here.

Here are some explanations for what you have observed that are consistent with the experimentally proven science:

A gas that is heavier than air will always diffuse and homogenize with the air. The heavier the gas, the longer it takes. CO2 and LPG (which actually has a very similar molecular weight to CO2) will take minutes to fully homogenize. However, no matter what the molecular weight of the gas is, diffusion begins instantly as soon as the container is open.

A gas that is heavier than air will collect in a pool under the following conditions: it is intoduced slowly to avoid turbulence and mixing, and the rate of introduction is faster than the rate of diffusion

A gas that is heavier than air, and that has a constant source, will collect at the ground while diffusion continuously occurs. If the source replenishes it faster than it diffuses, you will get a constant cloud of the gas near the ground. As soon as the source stops the cloud of gas begins to deplete as it continues to mix homogeneously with the air. This is why there are danger warnings on lpg vehicles, because a leak could create a source of lpg that lasts for hours which could create a dangerous cloud near the ground. Once the leak stops feeding the pool it will diffuse entirely into the atmosphere.

Now in a closed environment you have something else to consider: say you have 1 literof pure CO2 and you open the lid for a few seconds. In those few seconds diffusion occurred. 100% of the CO2 did not diffuse out, but some amount of air diffused in. Let's say for argument that 0.01 liters of air got in during those few seconds. Now the gas will homogenize and you will have a prefectly uniform mixture of CO2 and air that is 100 parts CO2 and 1 part air. Now if that mixture comes into contact with your beer, the newly introduced oxygen in the gas will oxidize your beer. It will not stay near the top where it first entered.

The common commercial oxygen target in the headspace of beer that I have seen is 0.01 parts per million to avoid staling. Now if you even open your keg for a second, it seems pretty likely that there is now more than 0.01ppm oxygen in your headspace.

 

[BrewnWKopperKat]

Gases will not mix until to expose them to each other. A sealed fermeter will be full of CO2. When you open it the CO2 and outside gasses will begin to mix.

So what are some pragmatic approaches (direct links to specific articles or book recommendations please) to minimizing oxygen ingress and/or mitigating oxidation?

Science is interesting. If engineering is converting science into useful things or processes, then maybe resources that talk about brewing engineering would be of interest to the forum.

 

[chipmunk]

How come I voted for blankets existing, but also agree entirely with @TheMadKing and @VikeMan‘s characterization of gasses?

A gas that is heavier than air, and that has a constant source, will collect at the ground while diffusion continuously occurs. If the source replenishes it faster than it diffuses, you will get a constant cloud of the gas near the ground.

Isn’t a constant cloud of gas near the ground = a blanket?

 

[TheMadKing]

So what are some pragmatic approaches (direct links to specific articles or book recommendations please) to minimizing oxygen ingress and/or mitigating oxidation?

Science is interesting. If engineering is converting science into useful things or processes, then maybe resources that talk about brewing engineering would be of interest to the forum.

This is valuable, thank you for continuing to push for a more practical approach. Here are some processes that I use to minimize oxidation:

I do not open the fermenter once fermentation has begun unless it is to add dry hops. I always dry hop during active fermentation to ensure that there is a constant source of CO2, and I purge the headspace afterward.

I liquid purge my kegs, meaning that I fill them to overflowing with starsan and push the liquid out with CO2 prior to kegging my beer. The kegs are never opened again after liquid purging.

I perform a closed transfer from the fermenter to the keg. I have a stainless conical and can push the beer to the keg under decent CO2 pressure. Before I had the conical I used a plastic carboy, so with a racking cane through a bung and a second hole in the bung for CO2, I could push the beer into my liquid purged keg. This method is not perfect but it is far better than a standard siphon.

Also before I had the conical, I did not cold crash my beer to avoid sucking air into the fermenter. I have seen others use CO2 filled balloons to mitigate this issue though.

I also recognize that bottled CO2 is not 100% pure CO2 gas and contains some percentage of air (probably about 0.01%) so I try to do as much as possible with the CO2 from fermentation which contains no air. I have used it to purge the starsan out of kegs, build pressure in the fermenter to carbonate my beer, etc

 

[TheMadKing]

How come I voted for blankets existing, but also agree entirely with @TheMadKing and @VikeMan‘s characterization of gasses?

Isn’t a constant cloud of gas near the ground = a blanket?

I recommend rereading my second to last paragraph above to illustrate the issue with how this thinking can cause damage to your beer.

Now in a closed environment you have something else to consider: say you have 1 literof pure CO2 and you open the lid for a few seconds. In those few seconds diffusion occurred. 100% of the CO2 did not diffuse out, but some amount of air diffused in. Let's say for argument that 0.01 liters of air got in during those few seconds. Now the gas will homogenize and you will have a prefectly uniform mixture of CO2 and air that is 100 parts CO2 and 1 part air. Now if that mixture comes into contact with your beer, the newly introduced oxygen in the gas will oxidize your beer. It will not stay near the top where it first entered.

 

[VikeMan]

This is valuable, thank you for continuing to push for a more practical approach. Here are some processes that I use to minimize oxidation:

I'll add...
- Use spunding valve instead of airlock
- Purge transfer hose before closed transfers
- Purgeable Hop Dropper for dry hopping

 

[VikeMan]

How come I voted for blankets existing, but also agree entirely with @TheMadKing and @VikeMan‘s characterization of gasses?

Isn’t a constant cloud of gas near the ground = a blanket?

You could call a concentration of a gas a blanket if you want. I think the folks voting "no such thing" (including me) voted in the context of the oft repeated and false claim in the homebrew community that it's impermeable.

Edit: In a fermenter, I'm talking about the CO2 that fills the entire head space as a result of fermentation. Not some distinct layer settling at the bottom, which doesn't happen.

 

[chipmunk]

Now in a closed environment you have something else to consider: say you have 1 literof pure CO2 and you open the lid for a few seconds. In those few seconds diffusion occurred. 100% of the CO2 did not diffuse out, but some amount of air diffused in. Let's say for argument that 0.01 liters of air got in during those few seconds. Now the gas will homogenize and you will have a prefectly uniform mixture of CO2 and air that is 100 parts CO2 and 1 part air. Now if that mixture comes into contact with your beer, the newly introduced oxygen in the gas will oxidize your beer. It will not stay near the top where it first entered.

Yes - completely agree. You’d need to replenish/purge the 0.01 l somehow to prevent oxidation before sealing the lid. But... how you answer depends on what you mean by “blanket” I suppose.

 

[Birrofilo]

@TheMadKing

Without quoting your last #102, what I get is that you do believe that it is possible to actually purge a volume and fill it with some gas, let's say CO2, which will be basically almost entirely CO2.
Some "perfect gas law" proponent here claimed in another thread this is not actually possible to purge a bottleneck because the gas you inject in the bottle neck will instantly diffuse in the atmosphere. I think we agree here.

Regarding diffusion of LPG after the initial collection on the ground, I certainly don't rule out that this is entirely possible, although so far I did not see anything in support of this, if not a generic belief that all gases mix uniformly given enough time, a belief which is based on the pure-gas equations, that certainly work in most cases, but I don't know whether it is true also for gases like LPG; but this is not the central point: The point here is that if time is needed for this diffusion to happen, then I, like other people using some chemical product, can purge a flask of chemical with LGP and close the cap, and I will have LPG inside the flask. And I can purge the bottleneck with CO2 and cap it and have much, much, much less air inside my bottleneck than if I had not purged it with CO2.

The common commercial oxygen target in the headspace of beer that I have seen is 0.01 parts per million to avoid staling. Now if you even open your keg for a second, it seems pretty likely that there is now more than 0.01ppm oxygen in your headspace.

This would be a very interesting discussion in another thread (How much oxygen is enough to spoil our beer) and I find it very interesting information.
Yet, I think you take this number too strictly.

If oxydation is nearly istantaneous (as somebody also claim) and it works on the entire content of the beer (as it appears to be generally cleaimed) as soon as you open your bottle, and even before you pour your beer in a glass, it would be stale. And not just a homemade raw-beer bottle, but also a commercial bottle.

Commercial producers aim high both because they can (their beer never sees "air", it's all a close circuit which recovers the CO2) and somehow because they must (their beer can travel for days under the sun or be stored and transported in the most punitive ways by certain customers). They aim at two years expiration date in possibly adverse conditions.

Our homemade bottle-refermented raw beer will probably be oxydized in 1 day if we put it on a truck and let it travel under the sun, shake etc.

And yet, even though oxydation certainly occurs in our bottle, I believe this is not an instantaneous phenomenon which takes place with 0,01 ppm in the bottle neck staling our beer. If you let a glass of beer exposed to air, it will take many hours to get darker (there is a brulosophy beerexperiment on this).

In another thread it was amply shown that purging the bottle neck with CO2 is definitely, and definitively helping the beer, which leads me to state that the purging operation is certainly useful, even though the complete elimination of air is never possible. It's a question of shades of grey, and we want to stay the more possible on the whitish side of grey.

Maybe another poll could be made: "do you believe that you can purge a container with CO2 and close the cap and in so doing greatly reducing the air content inside the container?" and "Do you believe that in so doing you reduce the oxydation of the beer to an extent which is perceptible in taste?"

 

[TheMadKing]

@TheMadKing

Without quoting your last #102, what I get is that you do believe that it is possible to actually purge a volume and fill it with some gas, let's say CO2, which will be basically almost entirely CO2.
Some "perfect gas law" proponent here claimed in another thread this is not actually possible to purge a bottleneck because the gas you inject in the bottle neck will instantly diffuse in the atmosphere. I think we agree here.

Regarding diffusion of LPG after the initial collection on the ground, I certainly don't rule out that this is entirely possible, although so far I did not see anything in support of this, if not a generic belief that all gases mix uniformly given enough time, a belief which is based on the pure-gas equations, that certainly work in most cases, but I don't know whether it is true also for gases like LPG; but this is not the central point: The point here is that if time is needed for this diffusion to happen, then I, like other people using some chemical product, can purge a flask of chemical with LGP and close the cap, and I will have LPG inside the flask. And I can purge the bottleneck with CO2 and cap it and have much, much, much less air inside my bottleneck than if I had not purged it with CO2.

The common commercial oxygen target in the headspace of beer that I have seen is 0.01 parts per million to avoid staling. Now if you even open your keg for a second, it seems pretty likely that there is now more than 0.01ppm oxygen in your headspace.

This would be a very interesting discussion in another thread (How much oxygen is enough to spoil our beer) and I find it very interesting information.
Yet, I think you take this number too strictly.

If oxydation is nearly istantaneous (as somebody also claim) and it works on the entire content of the beer (as it appears to be generally cleaimed) as soon as you open your bottle, and even before you pour your beer in a glass, it would be stale. And not just a homemade raw-beer bottle, but also a commercial bottle.

Commercial producers aim high both because they can (their beer never sees "air", it's all a close circuit which recovers the CO2) and somehow because they must (their beer can travel for days under the sun or be stored and transported in the most punitive ways by certain customers). They aim at two years expiration date in possibly adverse conditions.

Our homemade bottle-refermented raw beer will probably be oxydized in 1 day if we put it on a truck and let it travel under the sun, shake etc.

And yet, even though oxydation certainly occurs in our bottle, I believe this is not an instantaneous phenomenon which takes place with 0,01 ppm in the bottle neck staling our beer. If you let a glass of beer exposed to air, it will take many hours to get darker (there is a brulosophy beerexperiment on this).

In another thread it was amply shown that purging the bottle neck with CO2 is definitely, and definitively helping the beer, which leads me to state that the purging operation is certainly useful, even though the complete elimination of air is never possible. It's a question of shades of grey, and we want to stay the more possible on the whitish side of grey.

Maybe another poll could be made: "do you believe that you can purge a container with CO2 and close the cap and in so doing greatly reducing the air content inside the container?" and "Do you believe that in so doing you reduce the oxydation of the beer to an extent which is perceptible in taste?"

I think we are beginning to align. I don't agree with everything you've said and the concept of the "blanket" and purging are not the same thing. This may only be a terminology issue though

When some (most?) people use the term "CO2 blanket", it means an impermiable barrier of CO2 that will settle on top of your beer and prevent oxygen from reaching it and it will stay in that condition for minutes/hours/days etc

This is what is false. If you inject CO2 into a container of air and seal it, the CO2 will not simply settle to the bottom and stay there indefinitely. The two gasses will mix and become hemogenous.

Purging is the act of using a continuous source of CO2 to displace the air in a otherwise sealed container. This will absolutely remove/displace air and reduce oxidation effects. I don't believe anyone here has argued that this is not true.

In practice these two principals can be confused and misused. For example:

If you liquid purge a keg (this is the most effective method and eliminates virtually all air from the keg) and then open it, air WILL instantly enter your keg. Then when you seal it again, that air remains in the keg and mixes with the CO2 and oxidizes your beer over time.

If you purge a bottle with a continuous CO2 source, then immediately fill with beer and immediately cap on foam, you are not eliminating 100% of air, you're right. But it is certainly better than not purging with CO2, not because there is a blanket, but because there is temporarily a higher CONCENTRATION of co2 in the bottle than air.

The CO2 blanket idea implies that someone could squirt CO2 into a bottle, it will settle to the bottom and stay in the bottle like a liquid. Then they can go have a sandwich and watch a show, then come back awhile later to put beer into the bottle and the bottle and the CO2 is still protecting the bottle. This is false. The CO2 in the bottle will diffuse with the air and the rate of diffusion is determined by the molecular weight of CO2 and the size of the opening in the bottle (among other things like temp and pressure).

Your notion that "science" and "equations" do not match with real life is not correct. These ideas have been proven via experiments conducted in the 1860's and we're developed to explain physical observations exactly as you are doing now.

As for how much oxygen it takes to damage packaged beer to a threshold where someone can taste it... Now THAT is a good question. Since we don't know the exact amount, the best answer and the best practice is "as little as achievable"

 

[Birrofilo]

@TheMadKing

I have never read in any thread in other fora (I am new here) that somebody has such an extreme idea of CO2 "blanket" and heavy gases falling on the bottom with the same certainty that a liquid does.

The idea is generally that heavier gases will, with time, collect at the bottom if no perturbation is present. If you shake, gas mix. If you inject air, gas mix. The CO2 in gaseous form was used in the document to illustrate visually the behaviour that also LPG sports. It collects to the floor but it can be easily disturbed by a stream of air.

Your notion that "science" and "equations" do not match with real life is not correct. These ideas have been proven via experiments conducted in the 1860's and we're developed to explain physical observations exactly as you are doing now.

I never said that. I said that ideal-gas equations match quasi-ideal gas behaviour, but that some gases do NOT behave like the ideal-gas equations do, so it's your equations which don't match my real-life gases

I am not really interested in a discussion on gas equations (which would be way above my paygrade) but I think you could be satisfied by studying the "real gas equation" by Van del Waals (other models have also been proposed, for what I remember, this beeing one of the most quoted).

The van der Waals equation starts from the ideal-gas equation and introduces three new variables, which are gas-specific. For certain gases those values are such that the behaviour of the gas approximates an ideal gas, for other gases they are very far and the behaviour of the gas is far as well from the behaviour of an ideal gas. LPG, butane and propane being an obvious example from the real world.

Gases is a larger world than ideal gases, and physical observations have shown since ever that not all gases behave according to the ideal-gases laws. Your idea that all gases will behave according to the basic laws of ideal gases is flawed and this is demonstrated by the existence of many "real gas equations" (this is a work in progress in physics, we might see better equations in the future).

You and other continue to consider that all gases must, either istantaneously or at least ultimately, always behave like ideal gases, and this is a wrong assumption.

LPG does make strata, in a quite dramatic way.
Our homebrewing interest is understanding how much this behaviour is shared by CO2.
CO2 should exhibit a behaviour which is "somewhere" between LPG and an ideal gas.

Another misconception is that ultimately there is a lot of CO2 in normal air so the behaviour of CO2 is quite similar to normal air, but that again is not correct, there is only a tiny fraction of CO2 in normal air (0,04%), and CO2 is a different beast than normal air, and it is not an ideal gas, it is an "heavy" gas, and it has this tendency to collect on the bottom if left undisturbed.

 

[TheMadKing]

@TheMadKing

I have never read in any thread in other fora (I am new here) that somebody has such an extreme idea of CO2 and heavy gases falling on the bottom with the same certainty that a liquid does.

The idea is generally that heavier gases will, with time, collect at the bottom if no perturbation is present. If you shake, gas mix. If you inject air, gas mix. The CO2 in gaseous form was used in the document to illustrate visually the behaviour that also LPG sports. It collects to the floor but it can be easily disturbed by a stream of air.

No no no

Heavier gasses will NOT collect at the bottom with time. They will mix with time, on their own, without any shaking, mixing, turbulence, etc.

This is the critical point to understand. Gas molecules have energy. The higher the temperature of the gas, the more energy the molecules have. They are constantly moving and bouncing off each other. This energy causes gasses (all gasses, because it is a property of this state of matter) to mix on their own without any external influence. This is a gas law - which means that is has been experimentally demonstrated to be true in all cases, so many times and so thoroughly that it has been deemed a law and not a theory.

I also don't care to debate the applicability of every mathematical proof.

 

[Birrofilo]

No no no

Heavier gasses will NOT collect at the bottom with time. They will mix with time, on their own, without any shaking, mixing, turbulence, etc.

This is the critical point to understand. Gas molecules have energy. The higher the temperature of the gas, the more energy the molecules have. They are constantly moving and bouncing off each other. This energy causes gasses (all gasses, because it is a property of this state of matter) to mix on their own without any external influence. This is a gas law - which means that is has been experimentally demonstrated to be true in all cases, so many times and so thoroughly that it has been deemed a law and not a theory.

I also don't care to debate the applicability of every mathematical proof.

You are again using the ideal-gas reasoning. There are many forces acting on gas molecules. Again this is above my paygrade but there are other interactions, such as gravity, or gravitational attraction between particles, or other forms of forces. In perfect gases this constant motion is the only force at play, the others are not influencing the behaviour of the gas. In other non-perfect gases other forces have an effect and produce a different results.

Real-gas equations wouldn't exist if the ideal-gas equation worked for every gas!

(Please re-read my last post, I have this habit to continuously refine my text, and you are too fast in answering! Please see the Van der Waals equation of real gas, not the equation strictly, but the logic behind it).

 

[VikeMan]

The van der Waals equation starts from the ideal-gas equation and introduces three new variables, which are gas-specific. For certain gases those values are such that the behaviour of the gas approximates an ideal gas, for other gases they are very far and the behaviour of the gas is far as well from the behaviour of an ideal gas. LPG, butane and propane being an obvious example from the real world.

Is there something in the Van der Waals equation that suggests the heavier gas settling you keep referring to? Please be specific.

 

[Birrofilo]

Is there something in the Van der Waals equation that suggests the heavier gas settling you keep referring to? Please be specific.

Certainly but it's technical and above my paygrade as I said. They show deviation from "ideal" which means those gases don't behave as other ideal gases.

The Van der Waals equation "suggests" how to model the behaviour of a gas which does not behave according to the ideal-gas equation.
The Van der Walls equation is an extention of the ideal-gas equation, which applies to both ideal and non-ideal gases.

If you apply the gas-specific parameters to the single gas, and the gas is an ideal gas, you fall back to the ideal-gas equation because the van der Waals equation "becomes" the ideal-gas equation.

The more the three parameters deviate from those of an ideal gas, the more they form a Van der Waals gas-specific equation which is different from the ideal-gas equation, the more the gas will behave in a different and less-ideal way.

The less the behaviour is "ideal", the less the behaviour connected to the ideal behaviour applies, which includes the perfect mix, or the apparent non-response to the law of gravity, so to speak.

The fact that LPG falls to the ground is a fact of life, I repeat, which comes before any equation by any physicist.

The van der Waals equation shows you that the ideal-gas equation is not the alpha and omega of gas behaviour. Physicists know that not all gases behave the same and try to find a law of real gases because they know the ideal-gas law doesn't always apply.

LPG falls and I refer to it because it is a fact of life not because an equation states it. LPG is not an ideal gas. And CO2 is also not, although is less "weird" than LPG. And you cannot (entirely) explain their behaviour with the ideal-gas equation.

 

[Vale71]

Van der Waals equations offer more accurate modeling of gas behaviour at extremely high pressure or extremely low temperature. Within temperature and pressure ranges that are to be found in brewing (as opposed, for example, to the surface of Jupiter) the deviations are quite small. Regardless of the entity of the deviation this is a worthless and bogus argument anyway since gases are not suddenly going to start exibhiting completely divergent behaviour even at extreme conditions. All that is going to happen is that the values for temperature and pressure predicted based on the ideal gas law will differ from the actual values by some amount.

https://chem.libretexts.org/Bookshe...:_Real_Gases_-_Deviations_from_Ideal_Behavior

 

[Birrofilo]

Anybody is free to study the Van der Waals equation and understand how they apply to non-ideal gases.

And anybody is free to realize the obvious, that LPG falls to the ground, and it's a gas.