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CO2 blanket poll

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Is the CO2 blanket real or a myth

  • There’s no such thing ... gases mix

    Votes: 42 93.3%
  • It’s real ... CO2 is heavier than air and will settle forming a blanket

    Votes: 3 6.7%

  • Total voters
    45
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BrewnWKopperKat

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A sticky will not slay this myth....
"If you build it ([a sticky] and market it) they will come". There's a link button for the marketing step.

Plus helps reduce the need for large bold red letters. :yes:
 
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VikeMan

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I understand that gas initially mix, but I don't buy that they remain perfectly mixed forever.
The longer you wait, the more homogeneous the mixture. You can look at this as the fulfillment of Fick's Laws of Diffusion or as a manifestation of entropy. It's really both. Sorry to bring in a scientific explanation.

If the theory is that gases just mix perfectly forever, than how do you explain that propane and butane pose a safety risk because they tend to accumulate near the ground? They are gases, and they are "heavier than air" as is the common expression, and they do dangerously accumulate on the ground.
They tend to "accumulate" near the ground because that's where the leaks are happening, near the ground. Stop the leak (which otherwise continues to refresh the dense part of the gradient) and give it time, and the gases will fill whatever space is available, homogeneously. The molecular weight of gases is basically trivial compared with their kinetic energies. There are noticeable "permanent gradients" influenced by molecular weights when you compare gas mixtures at sea level vs the edge of our atmosphere, but on the scales we experience, no.
 

Vale71

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Guys, this is 18th Century physics, for crying out loud. The fact that adult, (presumably) educated people are actually having this discussion is simply appalling...
This really makes me sad and I'm not kidding.
 

doug293cz

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...

This experience shows how gas mix, not how they "separate" given enough time.
Are you saying that you believe after gases spontaneously homogenize (mix completely), that after some period of time they then spontaneously separate? Can you provide any evidence (like a video showing them "unmixing" similar to the one that shows how they mix)?

Brew on :mug:
 

Birrofilo

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They tend to "accumulate" near the ground because that's where the leaks are happening, near the ground. Stop the leak (which otherwise continues to refresh the dense part of the gradient) and give it time, and the gases will fill whatever space is available, homogeneously. The molecular weight of gases is basically trivial compared with their kinetic energies. There are noticeable "permanent gradients" influenced by molecular weights when you compare gas mixtures at sea level vs the edge of our atmosphere, but on the scales we experience, no.
No, absolutely not.
Propane, butane, propene and other gases, believe it or not, do accumulate to the ground because they are "heavier than air".

It is absolutely a given that LPG will accumulate on the "bottom" of the room or the container.
If you have a bottle and you fill it with LPG and air, the LPG will fall to the ground.

I am sure that you will be able to verify that with a quick search on the internet.

You can make an experiment: just close the windows in your basement, then open an LPG cylinder on the last steps of the staircase going to the basement, then remain on the upper floor.
You will feel the odour.

Now you light a lighter, while remaining on the upper floor: no explosion.

Then you throw the lighter on the basement (or anything incendiary) the your house will explode in a very spectacular way ;-)

The cylinder was almost on the ground floor, but the gas collected on the basement and that is why your house blew up.

Just ask anybody working with LPG or having a car going with LPG (5,6% of circulating cars in Italy, mine is one).

An LPG-car owner knows that he is forbidden to park on certain floors of a garage (garages which have a particular air circulation due to chemneys are exempted until -2 if memory serves). In normal garages an LPG car cannot be parked in an underground stage, whereas a methane car (CNG) can. Special parking places are reserved for LPG cars in parking lots with subterranean "grounds".

That is because CNG has a very different behaviour than LPG.

If you do a bit of searching around you will find this and I tell you this is physics, or if you prefer "real world physics".

For instance you can search for parking norms for LPG vehicles as opposed to parking norms for CNG vehicles.

Or just search for "propane heavier than air" etc. (or denser than air which is probably more correct, but people say "heavier").

EDIT: the different behaviour of LPG and natural gas is know to homebrewers who use LPG "turky friers" for their brewing needs. LPG accumulates on the ground where it can explode quite dramatically.
 
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Birrofilo

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Air is mostly CO2. Why isn’t all the CO2 on the ground with all the O2 way up high.
Because gases mix. Closed container or not, they mix.
Air is actually mostly nitrogen. CO2 is much less than 1%, 0,04% according to this source:

On the earth surface you have many motions of air due to temperature gradients: the sun doesn't heat all the Earth uniformly and you have several constant breezes, from sea to land and the other way round, from the mountains to the valley and the other way round, you have ascensional currents (used by sailplanes and birds to climb at high altitudes) and you have all sorts of winds. Air on the planet is continuously stirred.
 

Birrofilo

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Are you saying that you believe after gases spontaneously homogenize (mix completely), that after some period of time they then spontaneously separate? Can you provide any evidence (like a video showing them "unmixing" similar to the one that shows how they mix)?

Brew on :mug:
No, I don't say "gases". I say "which gases?". Denser gases will tend to fall to the bottom in the long run, absent perturbation. Propane, butane, propene (and LPG in general) being a clear and undeniable example of this.

If you study the behaviour of those gases you see that they are just "heavy" (dense) and they do collect at the bottom, given time.

Now, again given time, I do expect let's say in a mixture of CO2 and O2 that the denser of the two collects at the bottom, if not perturbed. It certainly happens with propane and I don't see why it shouldn't happen with CO2, even if more slowly.

I think you are mislead by considering the equations for perfect gases (ideal gases) but perfect gases don't exist and many gases show a behaviour which is far from the behaviour of ideal gas.
 

Birrofilo

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This might be an interesting source to read about the behaviour of LPG, it also shows CO2 being denser than air


The entire paper is interesting and it shows interesting images. I suggest you read it all, it is not long or abstruse.

If LPG shows this behaviour in a few seconds, with a density of 2,46 kg/m3, vs. a density of air of 1,20 kg/m3, I don't see why CO2, with a density of 1,96 kg/m3 cannot sport this behaviour after an undefined number of hours.

@VikeMan
 
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doug293cz

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No, I don't say "gases". I say "which gases?". Denser gases will tend to fall to the bottom in the long run, absent perturbation. Propane, butane, propene (and LPG in general) being a clear and undeniable example of this.

If you study the behaviour of those gases you see that they are just "heavy" (dense) and they do collect at the bottom, given time.

Now, again given time, I do expect let's say in a mixture of CO2 and O2 that the denser of the two collects at the bottom, if not perturbed. It certainly happens with propane and I don't see why it shouldn't happen with CO2, even if more slowly.

I think you are mislead by considering the equations for perfect gases (ideal gases) but perfect gases don't exist and many gases show a behaviour which is far from the behaviour of ideal gas.
No, denser gases tend to collect in low spots in the short run. Given time, all gases homogenize. Collection in low spots occurs when the rate of release of the denser gas is faster than the rate of diffusion causing homogenization. An LPG leak is an example of high rate of release.

Look at the video again. They start with the dense gas on the bottom, and the lighter gas on the top. The dense gas then rises, and the lighter gas sinks. Short term there is stratification, long term there is homogenization.

Brew on :mug:
 

Birrofilo

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No, denser gases tend to collect in low spots in the short run. Given time, all gases homogenize. Collection in low spots occurs when the rate of release of the denser gas is faster than the rate of diffusion causing homogenization. An LPG leak is an example of high rate of release.
Am I right in inferring that you did not read yet the document that I quoted in #51?

In the video, the denser gas is at the bottom at the beginning, it doesn't collect in low spots, and in the short run it mixes because the gas particles have this running behaviour.

But LPG does collect on the ground, from wherever you let it leak. If the ground is ventilated the gas is dispersed (because the air is disturbed by the "wind") if the ground is not ventilated the gas just sits on the floor and stays there. Even at 10 cm there is a much higher concentration than at 30 cm, as the paper shows experimentally, and "on the ground" there is more gas than at 10 cm. It really stratifies very much.

There is a picture where the behaviour of LPG is shown with some dry ice, which again has the same behaviour of LPG and sits in a very convincing way on the floor.

I don't ask you or anybody to "believe", but to understand the matter without preconceptions and prejudices. You might find that the laws of gas that you quote do not always apply in real world and in real situations (or in real bottle necks).
 
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TheMadKing

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This isn't something decided by popular opinion. It's a scientific fact. CO2 IS heavier than air, but gasses mix and the concept of a CO2 blanket is erroneous.

The only thing up for debate is how long it takes for CO2 to mix with an unacceptable amount of air in the size and shape of container you're using.

Good practice (being conservative) dictates that it happens instantly and you should do everything possible to minimize exposing a fermented beer to air.
 

TheMadKing

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Are you saying that you believe after gases spontaneously homogenize (mix completely), that after some period of time they then spontaneously separate? Can you provide any evidence (like a video showing them "unmixing" similar to the one that shows how they mix)?

Brew on :mug:
Or that you're breathing pure argon and or radon right now?
 

TheMadKing

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... if you are getting oxidation related flavors in your beer.
Or That anyone who tastes your beer can perceive? Maybe you just don't notice it?

I happen to be one that is sensitive to oxidation flavors (and they are many and varied) the common descriptor of cardboard is only one and it is an indicator of severe oxidation. You can also get acetaldehyde (green apple), dulling of malt and hop flavors, loss of hop esters, etc
 

BrewnWKopperKat

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I happen to be one that is sensitive to oxidation flavors (and they are many and varied) the common descriptor of cardboard is only one and it is an indicator of severe oxidation. You can also get acetaldehyde (green apple), dulling of malt and hop flavors, loss of hop esters, etc
No arguemet - everyone tastes beer differently (reference to study in The New IPA chapter 5).
 

TheMadKing

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Am I right in inferring that you did not read yet the document that I quoted in #51?

In the video, the denser gas is at the bottom at the beginning, it doesn't collect in low spots, and in the short run it mixes because the gas particles have this running behaviour.

But LPG does collect on the ground, from wherever you let it leak. If the ground is ventilated the gas is dispersed (because the air is disturbed by the "wind") if the ground is not ventilated the gas just sits on the floor and stays there. Even at 10 cm there is a much higher concentration than at 30 cm, as the paper shows experimentally, and "on the ground" there is more gas than at 10 cm. It really stratifies very much.

There is a picture where the behaviour of LPG is shown with some dry ice, which again has the same behaviour of LPG and sits in a very convincing way on the floor.

I don't ask you or anybody to "believe", but to understand the matter without preconceptions and prejudices. You might find that the laws of gas that you quote do not always apply in real world and in real situations (or in real bottle necks).
It isn't because air is disturbed by wind, it's because gasses mix homogeneously. The same effect will happen in a windless bubble full of air. If you inject LPG, it will initially fall and then eventually mix and remain mixed forever
 
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This isn't something decided by popular opinion. It's a scientific fact. CO2 IS heavier than air, but gasses mix and the concept of a CO2 blanket is erroneous.

The only thing up for debate is how long it takes for CO2 to mix with an unacceptable amount of air in the size and shape of container you're using.

Good practice (being conservative) dictates that it happens instantly and you should do everything possible to minimize exposing a fermented beer to air.
I'd say this is pretty much in line with my opinion- gas concentrations are different at different altitudes due to their densities, radon accumulates in basements, argon is suitable as welding shield gas, heavier than air gases are dangerous in confined spaces due to their tendency to displace atmospheric air. Air quality in confined spaces is a serious safety concern. All that being said, CO2 isn't all that heavy of a molecule compared to the rest of atmospheric air. Once you open your fermenter you're on borrowed time until the gas mixes. It's not instant, though. You can use the slightly heavier than air characteristic of CO2 to your advantage (not ruining a homebrew) as long as you don't treat it as magic.
 

madscientist451

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I think the poll could include another question, does it matter if you use a CO2 blanket or not?
Then run some kind of experiment and see if people can pick out the different beer in a triangle test.
Beer #1 Fill the keg with star san and push it out w/CO2, push the beer out of the fermenter, with CO2 into the keg.
Beer#2 Don't purge the keg, but create a CO2 blanket in the bottom, push the beer out of the fermenter with CO2 but maintain a Co2 blanket over the top of the beer.
I'll go out on a limb and predict that initially, you won't be able to tell the difference, but after 3-4 months you may be able to pick out the different beer.
 

BrewnWKopperKat

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@doug293cz , @Birrofilo - what if
  • "we" were to pause this discussion
  • allow the differing views (there may be more than two) time to create a "position" paper / statement
  • post the "position" paper / statement to allow people to read the content (this implies that the topic containing the position paper would be locked and no discussion would be allowed until people read the different positions)
  • then resume the discussion over in the brew science forum?
This approach may be a "product differentiator" for Homebrew Talk as it appears to me to be something that /rhomebrewing isn't structured to do.

It also allows for a well thought out position by each of the views.

Maybe the myth dies. Maybe it's not a myth under certain conditions that apply to homebrewing.
 

doug293cz

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Am I right in inferring that you did not read yet the document that I quoted in #51?

In the video, the denser gas is at the bottom at the beginning, it doesn't collect in low spots, and in the short run it mixes because the gas particles have this running behaviour.

But LPG does collect on the ground, from wherever you let it leak. If the ground is ventilated the gas is dispersed (because the air is disturbed by the "wind") if the ground is not ventilated the gas just sits on the floor and stays there. Even at 10 cm there is a much higher concentration than at 30 cm, as the paper shows experimentally, and "on the ground" there is more gas than at 10 cm. It really stratifies very much.

There is a picture where the behaviour of LPG is shown with some dry ice, which again has the same behaviour of LPG and sits in a very convincing way on the floor.

I don't ask you or anybody to "believe", but to understand the matter without preconceptions and prejudices. You might find that the laws of gas that you quote do not always apply in real world and in real situations (or in real bottle necks).
Yes, I read the paper. It says nothing to support that mixed gases spontaneously "unmix" or stratify. The paper is all about showing how active air flow will dissipate a transient blob of a gas faster than without active airflow. Nothing surprising there.

What you see with dry ice is a water droplet (very fine mist) cloud. CO2 is invisible. Water droplets are orders of magnitude heavier than gas molecules, so they will stratify (until the water evaporates, and the water vapor mixes with the air.)

Brew on :mug:
 

Pappers_

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The only thing up for debate is how long it takes for CO2 to mix with an unacceptable amount of air in the size and shape of container you're using.
Exactly, this is the crux of the question, and why the absolutist answers are not as helpful, perhaps. Its neither a myth nor an impermeable barrier. The answer to what is an unnacceptable amount of air will vary from brewer to brewer, process to process.

That being said, I appreciate these discussions and reminders of how little bits of our varied brewing practices can impact our beers.
 

TheMadKing

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Exactly, this is the crux of the question, and why the absolutist answers are not as helpful, perhaps. Its neither a myth nor an impermeable barrier. The answer to what is an unnacceptable amount of air will vary from brewer to brewer, process to process.

That being said, I appreciate these discussions and reminders of how little bits of our varied brewing practices can impact our beers.
No argument.. And any reference to "you" is the collective "you" not you personally.

So this is a risk management question really. I've done some risk analysis and it's a crapchute IMO.

The only way to eliminate risk is to have an absolute stance. 99% of the time this isn't possible (like risks to your health, risks to your life, etc). In those cases the absolute elimination of risk is not possible while maintaining an acceptable quality of life.

In this case we are talking about risk of oxidation to your beer. Luckily for us, the absolute answers that "all cold side oxygen is bad" and "preventing all contact with air is the most efficient method of reducing the risk oxidation" are easy enough to achieve.

These things are possible with some basic process modifications that are not difficult or expensive or unachievable for most. If folks intentionally want to introduce risk to all of their beers because a minor process change or minor expense is not "worth it" to them, that's fine and that's their business. However, it is a fact that these process improvements will result in beer that is superior to descerning tasters.

For folks that are brewing for themselves and their friends, and can't taste any difference, cool, you do you. However I believe this forum is a place where (newer) brewers should be able to come to learn the practices that will result in the best possible product they can make. The argument that the "CO2 blanket" is sufficient protection is simply not the best practice and is just confusing to people who don't know any better.

Know the "right way" and then choose "Another way" with eyes open if it suits you, but don't teach others that the "right way" is pointless because it's not the way you do things.
 
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Dgallo

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I stand with @TheMadKing on this very sentiment. Our jobs as experienced brewers should be to provide insight to the best practices, based in both scientific and anecdotal evidence. It’s then up to the reader if they feel the additional steps, equipment, or practice is worth it to their level of engagement in this hobby. The science is gases do mix and the scientific evidence was provided. Ask any brewer of heavily hopped beers how well the co2 blanket theory works, and anecdotally they will provide the answer for you with muted character and darkening of color.
 

BrewnWKopperKat

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These things are possible with some basic process modifications that are not difficult or expensive or unachievable for most.
In another topic, it was noted that one of the "problems" with homebrewing in 2020/2021 may be that there is "too much information" (or perhaps "too much discussion" or perhaps "too much debate").

Is there a single place where one can to go to read of those process modifications that you mentioned?
 

TheMadKing

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In another topic, it was noted that one of the "problems" with homebrewing in 2020/2021 may bei that that there is "too much information" (or perhaps "too much discussion" or perhaps "too much debate").

Is there a single place where one can to go to read of those process modifications that you mentioned?
I'm not arguing that this forum should exclude everything but "best practice", that's not what I intended to imply.

But it should not be a place for debating whether scientific fact is true or not IMO.

This thread started with that very debate and has morphed into

"well yeah we all agree that the CO2 blanket is not real, but now we don't care"

That's totally fine.

But in this time and place it is really important to keep that line clear between questioning whether scientific facts are really true, or whether you acknowledge the facts and make a decision that is not aligned with the majority.
 

BrewnWKopperKat

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Back in #65, I proposed the idea that the various "sides" could state their "position" for others to read/study/understand/contemplate.

So far, no response.
 

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I think some of the issues/differences in opinion relate to the degree to which gravity acts on gasses at different densities.. And what is meant by “blanket”. Here‘s a you tube video that I found showing bromine gas both above and below the air.
Gravity acts on the gas and causes it “mix“ downwards by gravity even as if diffuses. Both processes happen at the same time.
So... it depends on what is meant by “blanket”. If you just dump a one time shot of CO2 into a keg and expect it to drop and sit there and 100% protect the beer from oxygen, then no, blankets don’t exist. However, if you are supplying a steady mass flow of CO2, next to the beer surface, and if the mass flow into the region above the beer exceeds the mass flow of CO2 out of the region, then the CO2 concentration will increase over time until it reaches equilibrium - which means all the gas in that volume is pure, So in this sense, yes, a CO2 blanket can exist.
 
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VikeMan

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Regardless, in the end it all comes down to this...

Yep. And in reality, those molecules are very much smaller and more energetic. Even at 0 degrees C, O2 molecules for example move at about 500 meters per second. And those collisions are elastic. It's a Battle Royale with no winner, which gets more intense (energetic) at higher temps (which is what causes pressure to increase with increasing temperature as the molecules hit the walls more frequently).
 

VikeMan

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I just use sulfurhexafloride when I bottle. Give my brews a nice zing
I used to, but it kept reacting with water to make stinky H2S, O2, and toothpaste.
 
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