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

[Zadkiel]

That's pretty, but is there a purge valve I'm not seeing?

I don't know this model specifically, but yes, the general hop bong design has a gas post and pressure release valve to allow you to use CO2 to purge out the airlock contents.

here's a video of Kegland's one for the Brewzilla line.

 

[sibelman]

There IS a layer (which you could call a "blanket")

but

I wasn't claiming that the CO2 in the fermenter was magically protecting the beer from oxygen

it will take a lot longer than several minutes for the room air to disperse the C02.

but

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

Boiled down: oxygen-sensitive brews will be adversely affected by opening your fermenter, even briefly.

 

[PCABrewing]

Boiled down: oxygen-sensitive brews will be adversely affected by opening your fermenter, even briefly.

Well why didn't you just say that, sheesh.
I've been hanging on every post to get the final answer...
There is a collection of equations to answer the "how long" question, I found them on the internet.
If you really think it's worth it.

 

[doug293cz]

Well why didn't you just say that, sheesh.
I've been hanging on every post to get the final answer...
There is a collection of equations to answer the "how long" question, I found them on the internet.
If you really think it's worth it.

Go ahead and show us how those equations answer the question. The problem here is that initial conditions, boundary conditions, and the exact details of what air currents result from opening the lid on a bucket are almost totally unknown. And if you did know them in sufficient detail, they would only apply to one specific instance, and not generally across many different situations.

Brew on

 

[worlddivides]

Boiled down: oxygen-sensitive brews will be adversely affected by opening your fermenter, even briefly.

Exactly. But my argument wasn't addressing that. It was addressing Zadkiel's question about why the myth of the CO2 blanket won't go away, even though it's been known to be wrong for decades. And one reason I gave is the fact that, even though CO2 doesn't have a smell, it does burn your nostrils, make you lightheaded, and can make you lose consciousness at high concentrations. And the fact that there's still CO2 in a fermenter weeks after fermentation ended can make people wrongfully think that it's staying there because it's super heavy and will protect their beer. I imagine that most of them would go "Oh, right..." if you explained how oxygen will just mix with the CO2 if you open the fermenter since that's just how gases work, but I doubt many of them get that explanation.

I thought it was an easy way to understand why the myth won't go away, which was what the OP was asking.

It's one of the reason why, since starting kegging, I've only kegged my really hoppy beers and bottled the darker, maltier beers with the exception of a dry-hopped saison (which strangely enough still showed zero signs of oxidation 6 months after bottling, despite bottling from a bottling bucket) and an American Pale Ale (which I bottled directly from the fermenter out of paranoia of introducing oxygen).

The paranoia does get excessive. I'm thinking of just using carbonation tablets or individual dextrose dosing and bottling straight from the fermenter for my next hoppy beer just from imagining how much oxygen could be introduced using the bottling bucket.

 

[PCABrewing]

Go ahead and show us how those equations answer the question. The problem here is that initial conditions, boundary conditions, and the exact details of what air currents result from opening the lid on a bucket are almost totally unknown. And if you did know them in sufficient detail, they would only apply to one specific instance, and not generally across many different situations.

Brew on

So it sounds like it's not worth it.
Here's what I found and I also believe it would make for an interesting theoretical exercise that would have to be carried out for each physical environment and each batch and is unlikely to yield substantive improvement sufficient to justify the effort.
https://chem.libretexts.org/Courses...0.07:_Gas_Diffusion_and_Effusion-_Grahams_Law

I never said I could or would do it but I believe the toolkit exists to answer the "how long" question regarding the exposure to air. Do you disagree?

 

[Zadkiel]

I thought it was an easy way to understand why the myth won't go away, which was what the OP was asking.

It really did read like you were defending the myth. I think that's how everyone who read your post took it. Glad to hear it was an interpretation issue.

It's one of the reason why, since starting kegging, I've only kegged my really hoppy beers and bottled the darker, maltier beers with the exception of a dry-hopped saison

I bottle everything, and use a bottling bucket. I'm careful when syphoning from my fermenter to my bottling bucket not to do any un-necessary aeration, and I use oxygen-scavenging caps on my bottles (really have no idea if those are actually effective or not, but I use them because I like to believe they help). I've had absolutely zero problems with oxygenation. That said, I massively prefer dark beers and that dominates what I make, but not entirely, I've made my Pale Ale 3 times, that has late boil hops of EKG & Citra, and a dry hop of the same (no-where near to IPA levels, but a decent amount)) and no oxygen issues.

It makes me wonder where the line is. It apparently is a huge problem for NEIPA, but for me at least, it doesn't seem to be an issue with Pale Ale. What about XPA? IPA?

 

[worlddivides]

It really did read like you were defending the myth. I think that's how everyone who read your post took it. Glad to hear it was an interpretation issue.

It's just one of the annoying things about discussions online. On the one hand, not a single word I said was in defense of the myth, but because I'm not full-on bashing the people who believe the myth, people start off with the assumption that I'm trying to say that the myth is true (even though nothing I say is to that effect). I pointed out that a high concentration of CO2 makes your nostrils burn (a well-known fact) and someone responded with "CO2 is odorless, so what you're smelling isn't CO2" even though no one (not myself nor anyone else) said that CO2 "smelled like something." It's not an issue limited to online forums, and I've misread what other people have said too, so I'm guilty of it too from time to time.

It makes me wonder where the line is. It apparently is a huge problem for NEIPA, but for me at least, it doesn't seem to be an issue with Pale Ale. What about XPA? IPA?

I've never bottled an NEIPA and I don't ever intend to, but I have bottled some IPAs with very high hopping rates. Up until now, the highest hopping rate of anything I've bottled was 8 grams per liter for dry hopping (and 18 grams a liter when including kettle and whirlpool additions) and the color never changed. It was intensely hoppy until the last bottle, but it was less hoppy than when I first bottled it (which, admittedly, is to be expected). I do intend to bottle something with a higher hopping rate soon, so I'm thinking of trying a few methods like ascorbic acid.

The only experience I've personally had with oxidation has not been in kegs or in bottles, but has been in growlers. So I do think I'm probably overly paranoid, but it's possible that very paranoia that has protected my beers from oxidation.

When I transfer to a bottling bucket, I do it so it's just the beer going through the tubing into the priming sugar at a slow rate with zero splashing or anything. I cover the top of the bottling bucket with saran wrap (or sometimes just the lid. But it doesn't change the fact that the bottling bucket is full of air and the beer is constantly in contact with the air until the bottling process is complete. It makes me very uneasy, even though I honestly have only experienced oxidations in growlers so far.

 

[Alfgs]

I have always been really sensitive to how much an opened bottle of wine changes the days after you open it so I have always been very cautious with oxygen exposure no matter what I brew.

Sure, the wine might still taste good, but not as good as it did when you open it. So people think "I opened the fermenter a couple of times and it still tasted good, must be the co2 blanket" when their brew could have tasted even better.

I think the reason people believe in the co2 blanket is because we all watched movies or demonstrations like this in school.

 

[Zadkiel]

On the one hand, not a single word I said was in defense of the myth

It's down to one of the vagaries of the English language in that the subject of a statement doesn't have to be directly stated, but can be inferred. Your post started with:

"Why would it go away? There IS a layer (which you could call a "blanket") of CO2 over the beer."

Now to you, the 'it' of the question 'Why would it go away?' is the Myth, you're positing why would the myth go away? And when you read it back you only read it that way. But I think to everyone else the 'it' was interpreted as being the CO2 blanket, not the Myth, and that subject seems to be confirmed by your immediate next statement. So if you infer that the 'it' at the start is the CO2 blanket, and my OP talked about the CO2 rapidly diffusing/convecting away, you can see why it seemed like you were disagreeing.

Completely irrelevant to the discussion at hand of course, just explaining why people replied to you as though you were defending the myth.

 

[worlddivides]

It's down to one of the vagaries of the English language in that the subject of a statement doesn't have to be directly stated, but can be inferred. Your post started with:

"Why would it go away? There IS a layer (which you could call a "blanket") of CO2 over the beer."

Now to you, the 'it' of the question 'Why would it go away?' is the Myth, you're positing why would the myth go away? And when you read it back you only read it that way. But I think to everyone else the 'it' was interpreted as being the CO2 blanket, not the Myth, and that subject seems to be confirmed by your immediate next statement. So if you infer that the 'it' at the start is the CO2 blanket, and my OP talked about the CO2 rapidly diffusing/convecting away, you can see why it seemed like you were disagreeing.

Completely irrelevant to the discussion at hand of course, just explaining why people replied to you as though you were defending the myth.

Good point. I didn't even think of interpreting it that way.

 

[mac_1103]

I imagine that most of them would go "Oh, right..." if you explained how oxygen will just mix with the CO2 if you open the fermenter since that's just how gases work

And many of them would go "But CO2 is heavier than air."

It makes me wonder where the line is.

The line depends not just on the type of beer, but on how and how long you want to store it.

 

[Snuffy]

You never truly approach a protective effect until you achieve the elusive CO2 "Dutch Oven".

 

[BrewnWKopperKat]

I've never bottled an NEIPA and I don't ever intend to, but I have bottled some IPAs with very high hopping rates. Up until now, the highest hopping rate of anything I've bottled was 8 grams per liter for dry hopping (and 18 grams a liter when including kettle and whirlpool additions) and the color never changed. It was intensely hoppy until the last bottle, but it was less hoppy than when I first bottled it (which, admittedly, is to be expected). I do intend to bottle something with a higher hopping rate soon, so I'm thinking of trying a few methods like acid

Ascorbic acid could be viewed as 'cheap insurance' - it will help scavenge any oxygen that was added during bottling.

The New IPA (2019) has a bunch of information related to improving beer shelf life (yes, there's more to it than oxygen ingress).

When I transfer to a bottling bucket, I do it so it's just the beer going through the tubing into the priming sugar at a slow rate with zero splashing or anything. I cover the top of the bottling bucket with saran wrap (or sometimes just the lid. But it doesn't change the fact that the bottling bucket is full of air and the beer is constantly in contact with the air until the bottling process is complete. It makes me very uneasy, even though I honestly have only experienced oxidations in growlers so far.

(The context is open transfers and the case for using closed transfers well known). The unknowns seem to be 1) how rapidly does the oxygen ingress?, 2) how rapidly does oxidation start and have a negative taste impact on the beer?, and 3) how rapidly will oxygen mitigation ingredients remove the oxygen?

 

[worlddivides]

(The context is open transfers and the case for using closed transfers well known). The unknowns seem to be 1) how rapidly does the oxygen ingress?, 2) how rapidly does oxidation start and have a negative taste impact on the beer?, and 3) how rapidly will oxygen mitigation ingredients remove the oxygen?

Right. I think one reason I've never experienced oxidation is that I tend to consume most of my beers within 1-2 months. For kegs, the longest one lasts is typically 1.5 months. With bottles, the last few bottles might last up until 6 months, but even then, they're usually in the refrigerator at 3-4C (37F to 39F) for the vast majority of that time. So it's certainly possible that if I left them at room temperature for 6 months, I might taste oxidation.

 

[mashdar]

Right. I think one reason I've never experienced oxidation is that I tend to consume most of my beers within 1-2 months. For kegs, the longest one lasts is typically 1.5 months. With bottles, the last few bottles might last up until 6 months, but even then, they're usually in the refrigerator at 3-4C (37F to 39F) for the vast majority of that time. So it's certainly possible that if I left them at room temperature for 6 months, I might taste oxidation.

I'd go as far as to say certain styles may benefit from slow oxidation. I'm mostly thinking of quads and other big dark beers that peak after a year or two. I'm sure this is sacrilege to some, and I wouldn't suggest intentional exposure. (Diffusion through a cap/cork seems sufficient.)

 

[Zadkiel]

how and how long you want to store it.

For the purposes of my question, bottle on a shelf, and a reasonably long time (at least a year). Basically the worst case scenario. The line being between 'there is no issue whatsoever under any circumstances, expose away to oxygen and don't worry at all' and 'there could potentially be an issue'.

The first part would be identifying if that first side of the line is even true. I believe it is, but I don't have any actual proof, only my anecdotal evidence, my first ever brew, long before I had any concept of O2 exposure being an issue: fermenter opened multiple times during fermentation (I wanted to see what was happening!), dry hopped, then lavishly aerated during transfer from fermenter to bottling bucket (not deliberately, only realising it in hindsight), vigorously stirred to ensure my priming sugar was well mixed, bottled direct from the spigot without a bottling wand into thin PET bottles (a permeable material, and no oxygen scavenging cap) I recently opened a 9 month old bottle, and it had no sign at all of oxygenation (it's also possible that I'm not sensitive to it...). So I believe that line does exist.

Maybe one day I'll do it as an experiment, split a single unbittered pale ale wort into batches with different levels of dry hop, with no care for oxygen exposure, and leave them for a year, and see if I can find the hop level where the oxygenation has a noticeable effect. Could be fun.

 

[ScrewyBrewer]

but



but


Boiled down: oxygen-sensitive brews will be adversely affected by opening your fermenter, even briefly.

However, for the record, I wasn't claiming that CO2 in the fermenter was magically protecting the beer from oxygen.

 

[Yooper]

Whenever this conversation comes up, I always wish that someone would just do an experiment with an oxygen sensor stuck in the headspace above the wort and monitor its change in real time as a lid is removed and such. I think convection can be relatively minor, but Doug's point is key - it doesn't take much O2 ingress to make an effect.

but



but


Boiled down: oxygen-sensitive brews will be adversely affected by opening your fermenter, even briefly.

Here's something that almost never comes up. I am a winemaker as well, and one of the things I found most interesting a few years ago was studies showing oxidation with silicone bungs/stoppers, and even through airlocks via the cracks in the airlock. They were also looking at the (at the time) "new" plastic carboys, called Better Bottles. And then, we had similiar long lengthy discussions here on HBT about that. I was aging a huge beer on oak for a time, then wanted to bulk age longer and had a silicone type of closure and airlock.

I wish I could find the papers/experiments that I saw years ago. It actually showed the measurements in different types of fermenters, different types of airlocks, and different types of closures. It was pretty interesting. Every single one had o2 ingress, some alot more than others.

I used to get more involved in this "co2 blanket" topic discussions, but now I just got tired of beating my head against the wall. Once in a while, someone will quote the Ideal Gas Law, Boyle's Law, and then describe equilibrium. And someone else will say "Yes, but....my fermenter is airtight with an airlock". Sigh.