Can we dispel the myth of the 'CO2 Blanket' ?

[Zadkiel]

I see it so often repeated here.

In just the last 2 days I've seen 4 separate posts (and I don't read every thread, so there's probably more I missed) from people talking about how when opening a fermenter, there exists some sort of 'CO2 blanket' that protects your brew.

I'm sorry, but gas doesn't work that way. Convection and molecular diffusion of gasses between different concentration levels takes place almost instantly.

If CO2 somehow sinks to the bottom then we'd all be dead thanks to living in a CO2 blanket covering the planet. It doesn't work that way.

In reality, a 100% concentration of CO2 being exposed to a convecting atmosphere of 0.04% CO2 will diffuse in milliseconds, a few seconds at the outside. Likewise a 21% concentration of O2 being exposed to a bucket containing 0% O2 will likewise diffuse in milliseconds/seconds. Pressure differences, temperature differences and convection currents in the air all act to accelerate that process.

I've seen it argued that you can see the CO2 blanket from a dry ice (frozen/liquid CO2) machine - CO2 is colorless, you cannot 'see' it, what you see from a dry ice machine is condensation of water vapour in the air caused by the temperature difference between the rapidly expanding cooler gas and the air in the room, which then does drop down towards the floor and as it reaches higher concentrations, becomes visible. The white cloud is water, not CO2.

 

[BrewnWKopperKat]

Can we dispel the myth of the 'CO2 Blanket' ?

No.

Related question

​

Can we stop posting text that is statistically generated?​

​

 

[Zadkiel]

Can we stop posting text that is statistically generated?

Really not 100% sure what you mean by that, as nothing in my post had anything at all to do with statistics, but if you mean what I think you mean, then sure, I'll remove it. It was only there to support my argument, not as primary evidence, so I've no issue removing it, it changes nothing.

 

[BrewnWKopperKat]

 

[Cheshire Cat]

I see it so often repeated here.

In just the last 2 days I've seen 4 separate posts (and I don't read every thread, so there's probably more I missed) from people talking about how when opening a fermenter, there exists some sort of 'CO2 blanket' that protects your brew.

I'm sorry, but gas doesn't work that way. Convection and molecular diffusion of gasses between different concentration levels takes place almost instantly.

If CO2 somehow sinks to the bottom then we'd all be dead thanks to living in a CO2 blanket covering the planet. It doesn't work that way.

In reality, a 100% concentration of CO2 being exposed to a convecting atmosphere of 0.04% CO2 will diffuse in milliseconds, a few seconds at the outside. Likewise a 21% concentration of O2 being exposed to a bucket containing 0% O2 will likewise diffuse in milliseconds/seconds. Pressure differences, temperature differences and convection currents in the air all act to accelerate that process.

I've seen it argued that you can see the CO2 blanket from a dry ice (frozen/liquid CO2) machine - CO2 is colorless, you cannot 'see' it, what you see from a dry ice machine is condensation of water vapour in the air caused by the temperature difference between the rapidly expanding cooler gas and the air in the room, which then does drop down towards the floor and as it reaches higher concentrations, becomes visible. The white cloud is water, not CO2.

Look in this modern age we should be discussing the CO2 Duvet.

 

[fluketamer]

it took me a while to figure out this thread. im slow.

i read an article a few days ago that referenced "the blanket" . i think i saw a post a few days ago too. i think i saw it said that air is mostly nitrogen so the amount of o2 is even lower than one would think.

its prolly likely, that in a very heavily dry hopped beer like 2 plus oz per gallon, the small amount of oxygen that gets into a fermenter during old timey dry hopping methods is eonugh to be a significant problem. i havent done a side by side test. i am sure brulosophy will have a similar experiment with useless statistical value. but i have immediately noticed the diffrence in hop preservation when i limited my o2 exposure as much as i can , even on low hop dosing rates.

i think when it was standard to just open the bucket and throw em in, nobody was using such huge dry hopping rates and it prolly didnt really matter.

i think the blanket idea is for those of us who havent made the jump to fully oxygen free dry hopping ( myself included) to rationalize there process. i think people who rely on and post about the blanket dont have pressure fermenting ca[abilities. but its just speculation.

btw, i didnt use any AI in generating ( lol) this post.

 

[mashdar]

Dispelled multiple tumes over the decades. Won't die.
https://www.homebrewtalk.com/threads/the-protective-co2-blanket.303980/

 

[Beekeeper]

A fluffy, frothy krausen is what I might consider a protective CO2 blanket.

But my fermenter(s) stay closed to the atmosphere once fermentation has begun.

 

[BrewnWKopperKat]

Dispelled multiple tumes over the decades. Won't die.

It's one of a number of topics that will keep coming back ...

... as long as there are new brewers coming to discussion forums.

 

[Zadkiel]

i read an article a few days ago that referenced "the blanket" . i think i saw a post a few days ago too. i think i saw it said that air is mostly nitrogen so the amount of o2 is even lower than one would think.

Nitrogen levels don't matter, what matters most is the concentration difference in CO2 in the fermenter (hopefully close to 100%) and the concentration in the air surrounding it (CO2 at ground level is approx 0.04% - used to be 0.02%) that huge difference causes diffusion to happen extremely rapidly. If there was little to no convection happening, then diffusion might happen over the course of seconds, but in the presence of any convection (which happens naturally within your house, you're unaware of it but the air in your house is under a constant state of convection) it will take milliseconds. In the opposite direction, the 21% concentration of O2 in the air will diffuse rapidly into the 0% (or as close to it as makes no difference) O2 inside the bucket.

A fermenter with a narrow neck, or a small opening, will reduce the effect of convection to some extent. Not prevent, just reduce (popping off an airlock for a few seconds isn't going to let much in). It won't prevent diffusion, but it will take longer to reach full saturation, maybe even long enough that if you're quick enough it won't reach full 21% O2 inside, but I most commonly see the 'CO2 Blanket' being used giving advice to new brewers using plastic buckets, and if you're taking the lid off a bucket, before the lid has even been removed, the gas inside will be mixed to atmospheric levels, it's just simply not true.

 

[Zadkiel]

Look in this modern age we should be discussing the CO2 Duvet.

Nooo, duvets are warmer, and diffusion happens quicker at higher temperatures, a CO2 Duvet would vanish much faster than a CO2 blanket would!

 

[mac_1103]

I see it so often repeated here.

And immediately debunked every time. We can only do so much.

 

[Zadkiel]

And immediately debunked every time. We can only do so much.

Not the ones I've seen recently, I think people just got sick of repeating themselves over and over, that's why I thought a full thread about it might work better, for a while at least.

 

[An Ankoù]

I see it so often repeated here.

In just the last 2 days I've seen 4 separate posts (and I don't read every thread, so there's probably more I missed) from people talking about how when opening a fermenter, there exists some sort of 'CO2 blanket' that protects your brew.

I'm sorry, but gas doesn't work that way. Convection and molecular diffusion of gasses between different concentration levels takes place almost instantly.

If CO2 somehow sinks to the bottom then we'd all be dead thanks to living in a CO2 blanket covering the planet. It doesn't work that way.

In reality, a 100% concentration of CO2 being exposed to a convecting atmosphere of 0.04% CO2 will diffuse in milliseconds, a few seconds at the outside. Likewise a 21% concentration of O2 being exposed to a bucket containing 0% O2 will likewise diffuse in milliseconds/seconds. Pressure differences, temperature differences and convection currents in the air all act to accelerate that process.

I've seen it argued that you can see the CO2 blanket from a dry ice (frozen/liquid CO2) machine - CO2 is colorless, you cannot 'see' it, what you see from a dry ice machine is condensation of water vapour in the air caused by the temperature difference between the rapidly expanding cooler gas and the air in the room, which then does drop down towards the floor and as it reaches higher concentrations, becomes visible. The white cloud is water, not CO2.

Let's not get carried away here.
Yes there is a CO2 blanket within an active fermenter. The yeast uses the oxygen to produce ethanol and carbon dioxide and the headspace contains mainly CO2 because of the slightly positive pressure in the fermenter and the inability for atmospheric gases to pass through the airock. As long as the beer is fermenting and the container remains closed, any other gas (nitrogen mainly) is purged through the airlock. Once the fermenter is opened, however, the principles that @Zadkiel mentions above start coming into play and the "blanket" will rapidly disperse as the headspace gases and the atmosphere diffuse into each other. If the beer is sightly warmer than ambient temperature this will happen more quickly because of convection.
As long as we don't open the fermenter too often, we should be safe from oxygen ingress as long as the beer is fermenting and remains saturated with CO2.

Many English ales were traditionally made using open fermenters. I haven't tried it yet, but I'll bet the beer tastes different to the same beer made in a closed system. Not because of oxidation but because the yeast would have greater opportunity for aerobic fermentation.

 

[Bobby_M]

Not the ones I've seen recently, I think people just got sick of repeating themselves over and over, that's why I thought a full thread about it might work better, for a while at least.

Creating a specific thread about it really isn't going to be any more impactful than spot-correction as you see it come up. It assumes everyone reads every thread before having random conversations. No one that spends any significant time around here thinks CO2 acts as a barrier.

 

[BrewnWKopperKat]

I think people just got sick of repeating themselves over and over, that's why I thought a full thread about it might work better, for a while at least.

You can work towards dispelling the myth by having a well written (and peer reviewed) response to post in any new topic.

You can monitor various home brewing discussion forums for topics where including the response is appropriate.

It will likely take 3 to 5 years for the old topics to 'age out' (as new brewers typically don't pay attention to older content).

 

[worlddivides]

Why would it go away? There IS a layer (which you could call a "blanket") of CO2 over the beer. I recently did a closed transfer of a beer 15 days after pitching yeast. Fermentation had been finished for almost two weeks, yet after the closed transfer when I opened the fermenter for the first time and stuck my head in to smell it, I almost collapsed from all the CO2 in there which burned my nostrils and made me very light headed. Not the first time this had happened, but previously it had been closer to the end of fermentation. This is in a beer that had finished fermentation about 11-12 days earlier.

Granted, I had never opened the fermenter before that point and I wasn't claiming that the CO2 in the fermenter was magically protecting the beer from oxygen, but some people seem to think that all the CO2 in there just 100% leaves out of the airlock and you're left with a vacuum in the fermenter. That doesn't happen and neither does the CO2 stay like a stone anchor on the bottom, but it's something that any brewer can experience that can back up their belief that the CO2 is "blanketing" the beer.

 

[Broken Crow]

Up Next:
"When do I rack to Secondary?"

 

[MaxStout]

View attachment 885033
Up Next:
"When do I rack to Secondary?"

As soon as you can, before the yeast autolyze and you get off-flavors.

/sarcasm

 

[Bobby_M]

Why would it go away? There IS a layer (which you could call a "blanket") of CO2 over the beer. I recently did a closed transfer of a beer 15 days after pitching yeast. Fermentation had been finished for almost two weeks, yet after the closed transfer when I opened the fermenter for the first time and stuck my head in to smell it, I almost collapsed from all the CO2 in there which burned my nostrils and made me very light headed. Not the first time this had happened, but previously it had been closer to the end of fermentation. This is in a beer that had finished fermentation about 11-12 days earlier.

Granted, I had never opened the fermenter before that point and I wasn't claiming that the CO2 in the fermenter was magically protecting the beer from oxygen, but some people seem to think that all the CO2 in there just 100% leaves out of the airlock and you're left with a vacuum in the fermenter. That doesn't happen and neither does the CO2 stay like a stone anchor on the bottom, but it's something that any brewer can experience that can back up their belief that the CO2 is "blanketing" the beer.

Because the context/practical application for "blanket of CO2" is protective, meaning that it is an effective barrier for O2 exposure, which it is not. The claim that a layer of CO2 is protective is also in the context of the headspace being open to room air where oxygen COULD enter but the "co2 blanket" was there to stop it from touching the beer.

No one has ever claimed that the CO2 in a closed system disappears.

 

[ScrewyBrewer]

Why would it go away? There IS a layer (which you could call a "blanket") of CO2 over the beer. I recently did a closed transfer of a beer 15 days after pitching yeast. Fermentation had been finished for almost two weeks, yet after the closed transfer when I opened the fermenter for the first time and stuck my head in to smell it, I almost collapsed from all the CO2 in there which burned my nostrils and made me very light headed. Not the first time this had happened, but previously it had been closer to the end of fermentation. This is in a beer that had finished fermentation about 11-12 days earlier.

Granted, I had never opened the fermenter before that point and I wasn't claiming that the CO2 in the fermenter was magically protecting the beer from oxygen, but some people seem to think that all the CO2 in there just 100% leaves out of the airlock and you're left with a vacuum in the fermenter. That doesn't happen and neither does the CO2 stay like a stone anchor on the bottom, but it's something that any brewer can experience that can back up their belief that the CO2 is "blanketing" the beer.

Anyone using a chest freezer for fermenting their beer will agree that, since C02 is heavier than room air, it accumulates and stays inside a chest freezer. One whiff is enough to burn your nostrils and snap your head back. And it will take a lot longer than several minutes for the room air to disperse the C02.

 

[Broken Crow]

 

[Zadkiel]

You can work towards dispelling the myth by having a well written (and peer reviewed) response to post in any new topic.

You can monitor various home brewing discussion forums for topics where including the response is appropriate.

Sorry but I'm not prepared to take on that level of responsibility and that much work, and be 'that guy' who constantly **** posts in multiple threads telling people they are wrong. However I was prepared to make a thread in the hope that some of the people who are /currently/ posting here and making claims about the CO2 blanket would see it without being directly confronted about it. As I said before, if it works, it'll only be effective for a while, but honestly that's all I'm prepared to do.

 

[An Ankoù]

As I said before, if it works, it'll only be effective for a while, but honestly that's all I'm prepared to do.

And what you've done is enough. You can lead a horse to water, but you can't make him drink beer.

Whatever people are smelling in chest freezers or fermenters isn't CO2, which is odourless. I'm not suggesting there isn't CO2 in there as well.

 

[Broken Crow]

Sorry but I'm not prepared to take on that level of responsibility and that much work, and be 'that guy' who constantly **** posts in multiple threads telling people they are wrong.

I know what's it's like to have seemingly continually affronts to the day, so I made this thread that you might enjoy and maybe make use of just to vent:
https://www.homebrewtalk.com/thread...d-or-entertainment-for-regular-hbters.701252/
I feel your frustration.

 

[doug293cz]

And what you've done is enough. You can lead a horse to water, but you can't make him drink beer.

Whatever people are smelling in chest freezers or fermenters isn't CO2, which is odourless. I'm not suggesting there isn't CO2 in there as well.

No you don't smell the CO2, but in contact with the moisture in your sinuses and airways, CO2 forms carbonic acid which will cause a burning sensation if you breath in air with high concentrations of CO2.

Brew on

 

[Zadkiel]

Anyone using a chest freezer for fermenting their beer will agree that, since C02 is heavier than room air, it accumulates and stays inside a chest freezer. One whiff is enough to burn your nostrils and snap your head back. And it will take a lot longer than several minutes for the room air to disperse the C02.

Diffusion by itself is slow. Diffusion happens magnitudes faster in the presence of convection. A closed chest freezer is not perfectly air tight but it is well enough that the natural convection currents in the room will not affect the inside while sealed. When opened it becomes open to convection but it's size and shape will somewhat protect it and yes, it'll take a little while to completely diffuse.

Opening a plastic bucket standing in a room, or even inside a fermentation fridge, immediately exposes the gas headspace inside to the full effects of convection, furthermore the pressure inside the fermenter will have been at a slightly higher pressure than atmosphere, not much more, but enough to create it's own convection current when it's opened. That pressure differential doesn't happen when opening a freezer as it's not a sealed environment.

And even if there is some layer of CO2 that remains at high densities, that in no way whatsoever would prevents O2 from entering that space. The CO2 'blanket' is imagined as some protective layer that is somehow repelling O2 from entering it, when in fact it does no such thing.

The laws that govern the diffusion of gasses are identical to the laws of fluid dynamics, gasses behave like, and are treated as, liquids in the relevant equations. Ask yourself this, if this situation was switched but instead of gasses we substitute liquids - our 'room' is underwater with a slow moving current and inside the bucket is a solid mass with a layer of milk on top of it at a slightly higher pressure, and then the bucket is opened, how long do you think it would be before the water saturates the bucket headspace. Do you think you could open that bucket for, say, 3 seconds and seal it again without there being a large amount of water inside when you seal it?

 

[Zadkiel]

I know what's it's like to have seemingly continually affronts to the day, so I made this thread that you might enjoy and maybe make use of just to vent:
https://www.homebrewtalk.com/thread...d-or-entertainment-for-regular-hbters.701252/
I feel your frustration.

Damnit, that's a damn good call. I've seen that thread before and should have thought of it. Sorry.

 

[Bobby_M]

I completely understand encountering bad arguments and false information stated as fact. Luckily here, only a hobby is mildly affected. Bigger fish to fry and all that.

 

[doug293cz]

Time to repost this video that explains and demonstrates gas diffusion. It the absence of air currents (convection) the time scale for relatively complete diffusion (over distances less than ~1 meter) is minutes or 10's of minutes, not milliseconds/seconds. However, since it takes less than 1 ppm total dissolved O2 to oxidize beer over days/weeks, it only takes seconds of air exposure to the fermenter or keg headspace to get enough O2 diffused/convected into the headspace to cause issues down the line.



Brew on