anticipating having to restart a stuck WY3724 saison

[Tom R]

I'm planning my first saison. I'm considering using 3724, and realize that it tends to stick around 1.035, and that adding a second strain such as 3711 can prevent this.

So how is this done? Should I pitch the 3724, let the temp climb into the high 80s-low 90s, and wait for it to stick, then reduce temp to about 70F and pitch the less heat-tolerant 3711?

I guess I could just use 3711 alone, but it seems that saisons benefit from the esters caused by really high temp fermentation, and the 3711 apparently maxes out at 77F.

Thoughts?

 

[Gregory T]

there is a great article about 3724. basically open primary for 8 days. I have brewed 3 without the Dupont stall this way. The theory is the yeast is sensitive to pressure.

https://www.maltosefalcons.com/tech/guide-saisons-and-saison-yeasts

 

[Vale71]

That theory is bullcrap and should be completely disregarded. An airlock will at most give you a couple millibars over ambient pressure and no yeast is so sensitive that it will be affected by that. And that's ignoring the fact that weather variations can cause the ambient pressure to vary by as much as 20 millibar and that pressure in a bottle can exceed 3 bar, which means bottle conditioning with this yeast should be utterly impossible which is really not the case.

 

[Gregory T]

That theory is bullcrap and should be completely disregarded. An airlock will at most give you a couple millibars over ambient pressure and no yeast is so sensitive that it will be affected by that. And that's ignoring the fact that weather variations can cause the ambient pressure to vary by as much as 20 millibar and that pressure in a bottle can exceed 3 bar, which means bottle conditioning with this yeast should be utterly impossible which is really not the case.

That’s an interesting opinion

The facts are, I brewed 3 saisons back to back to back without an airlock which hit FG’s of 1.002, 1.001 and 1.002 in 8 days with nothing but aluminum foil over the airlock

whether it’s pressure that stalls it or something else, if you want to avoid the DuPont stall I recommend no airlock

 

[Miraculix]

I guess it's more about slightly elevated oxygen levels and slightly lower co2 levels within the wort during fermentation.

I also read that multiple people didn't get this stalling issue without the airlock so chances are high that it works.

The bottle conditioning happens with simple sugars, the stalling happens when there are no simple sugars left as those get eaten first, so the comparison does not really point to something, although I also think that pressure is probably not the variable to look at to explain this phenomena.

 

[govner1]

If you experience a stuck fermentation with 3724 I’ve had success getting it it going using T58.
Rehydrate the T58 and before pitching add a couple of tablespoons of bottled OJ (not frozen) and it will take off!

 

[Vale71]

That’s an interesting opinion

The facts are, I brewed 3 saisons back to back to back without an airlock which hit FG’s of 1.002, 1.001 and 1.002 in 8 days with nothing but aluminum foil over the airlock

whether it’s pressure that stalls it or something else, if you want to avoid the DuPont stall I recommend no airlock

It's not an opinion, it's an observation based on a scientific understanding of the situation. Anything else is just ridiculous superstition and will have the same effect as ritualistic chanting or the cerimonial slaughtering of a goat.
Here is another scientific fact. If you remove the airlock you reduce the headspace pressure by let's say 2 millibars. However hydrostatic pressure will give you the same pressure you had at the surface with airlock on and that allegedly caused the yeast to give up and die about 2 centimeters below the surface of the beer. Basically, you just moved this imaginary line-of-death down 2 centimeters and that is supposed to make the difference between a regular fermentation and a stuck fermentation? Give me a break...

 

[Gregory T]

It's not an opinion, it's an observation based on a scientific understanding of the situation. Anything else is just ridiculous superstition and will have the same effect as ritualistic chanting or the cerimonial slaughtering of a goat.
Here is another scientific fact. If you remove the airlock you reduce the headspace pressure by let's say 2 millibars. However hydrostatic pressure will give you the same pressure you had at the surface with airlock on and that allegedly caused the yeast to give up and die about 2 centimeters below the surface of the beer. Basically, you just moved this imaginary line-of-death down 2 centimeters and that is supposed to make the difference between a regular fermentation and a stuck fermentation? Give me a break...

Please enlighten us on your proofs. So far All I hear is opinion.

My proof is I brewed 3 saisons back to back to back with 3724 and they reached FG in 8 days. No DuPont stall

Would you prefer the word hypothesis? A scientific name for an unproven opinion

Like that the universe revolved around the earth which was also flat

 

[Dland]

This is probably a dumb question; but why would you use a yeast that you think tends to get stuck in the first place. Is it that unique?

Off topic a bit, but dry pitched some BE-134 saison yeast for the first time today, it is already working.

 

[Gregory T]

This is probably a dumb question; but why would you use a yeast that you think tends to get stuck in the first place. Is it that unique?

Off topic a bit, but dry pitched some BE-134 saison yeast for the first time today, it is already working.

For its characteristics and if you leave off the airlock it doesn’t stall

 

[Tom R]

This is probably a dumb question; but why would you use a yeast that you think tends to get stuck in the first place. Is it that unique?"

I chose this strain because it seems popular and the Wyeast description appeals to me:

"This strain is the classic farmhouse ale yeast. A traditional yeast that is spicy with complex aromatics, including bubble gum. It is very tart and dry on the palate with a mild fruitiness. Expect a crisp, mildly acidic finish that will benefit from elevated fermentation temperatures. "

And although stalling isn't a foregone conclusion, it seems easy enough to counter by pitching another strain. I just wanted some thoughts on how to go about it.

I'll certainly consider other yeasts suitable for a saison, nothing is cast in stone here!

 

[Qhrumphf]

I've read the backpressure/open ferment bit as well as the proposed biology behind it. And I think it applies to commercial scale far more than homebrew scale, where the pressure differentials are higher.

I've never had it stall on me. And that's using airlocks and blowoffs. But I also crank it hot (95-100F). But I've never used it straight on larger scale either (only blends containing Dupont along with less finicky strains, and there only into the mid 80s). The difference I've read (not confirmed personally) is that lower pressure alleviates the need for extreme temps.

Or just use a blend. Or dual strain works too.

3711 also does just fine fairly hot. My experience, if you're pitching enough yeast and aerating properly, it's difficult to get too hot for most Belgian yeasts.

So I'd save a liter of your wort, ideally sterile. Let your main fermrntation climb to the mid upper 80s. Once fermentation starts to slow, pitch 3711 into your saved liter, let it get really active (maybe 16-24 hrs), then pitch it all leaving it at your existing mid upper 80s ferment temp.

 

[Tom R]

Whoops, I screwed up the quote. Still figuring out how to quote responses...

 

[Miraculix]

This is probably a dumb question; but why would you use a yeast that you think tends to get stuck in the first place. Is it that unique?

Off topic a bit, but dry pitched some BE-134 saison yeast for the first time today, it is already working.

I tried that one on a very low abv brew (about 2.3%), came almost out as clean as a lager... not what I was intending for, but still a delicious brew.

 

[Qhrumphf]

Also, bear in mind that 3711 is the Holy Mother of diastaticus yeast strains. Be very mindful of anything that yeast touches, and be extra dutiful in cleaning and sanitizing them.

Lest a bit survive and over-attenuate future non-Saisons you brew.

I treat diastaticus yeast strains with the same deference I treat Brett.

Also worth pointing out most if not all OTHER saison yeasts are ALSO diastaticus. I do believe the Dupont strains (WY3724 and WLP565) carry STA1, although in my experience they don't go to the level that 3711 does. 3711 is the only non-mixed ferm sour beer ferment I've had to super-attenuate (exceed 100% apparent attenuation ie ferment below 1.000)

 

[ChuckS1]

I've brewed three saisons with 3724 using the Maltose Falcon open fermentation process and have not had a stall yet or had to get to crazy high temps that some people say are needed. Open fermentation works.

 

[Vale71]

I've read the backpressure/open ferment bit as well as the proposed biology behind it. And I think it applies to commercial scale far more than homebrew scale, where the pressure differentials are higher.

Hydrostatic pressure is definitely a concern in large scale commercial operations where you have fermenters that are up to three stories high. Pressure at the bottom can reach 1 bar and that's just from hydrostatic pressure alone. Pressure from an airlock doesn't exceed 1-2 mbar and that's peanuts compared to the former case.

 

[Vale71]

My proof is I brewed 3 saisons back to back to back with 3724 and they reached FG in 8 days. No DuPont stall

And I've brewed 3 saisons back to back with 3724 while all the time dancing around the fermenter and chanting and they didn't stall. This is proof that you must do this to prevent stalled fermentations with this strain.
If you don't see that our two statements are equally meaningless vis-a-vis proving causation then I'm just wasting time trying to make you understand.

 

[Qhrumphf]

Hydrostatic pressure is definitely a concern in large scale commercial operations where you have fermenters that are up to three stories high. Pressure at the bottom can reach 1 bar and that's just from hydrostatic pressure alone. Pressure from an airlock doesn't exceed 1-2 mbar and that's peanuts compared to the former case.

Yep. And majority (i can think of at least one exception though I don't think the particular setup is still used) of commercial breweries practicing open fermentation are using a different fermenter geometry than a tall cylindroconical (instead short and wide) to lessen that hydrostatic pressure at the same time

Also worth pointing out the beer doesn't stay there long. As soon as it slows down it's immediately into a sealed tank.

 

[myndflyte]

I've pitched both 3724 and 3711 at the same time just in case it stalled. Also, I've pushed 3711 over 80F with no issues. 3711 is a beast though. It's taken the last 2 saisons I've done down to 1.000. But I've never had any issues with it over attenuating the next beer I brew in that bucket. Just use good cleaning and sanitation processes.

 

[couchsending]

Add 2g of Belle Saison when you pitch the 3724. No stalling.

 

[Gregory T]

And I've brewed 3 saisons back to back with 3724 while all the time dancing around the fermenter and chanting and they didn't stall. This is proof that you must do this to prevent stalled fermentations with this strain.
If you don't see that our two statements are equally meaningless vis-a-vis proving causation then I'm just wasting time trying to make you understand.

Magic is just science we don’t understand.

Once again where are your proofs. You have none just an idea. You can’t prove a hypothesis with your thoughts. There are plenty of scientists who THOUGHT many things were just not possible

Unfortunately, despite the fact that you have multiple tests that show the DuPont stall can be avoided with an open primary you refuse to believe it, accept it, or even attempt to disprove it

A closed mind is not scientific

An airlock equals a DuPont stall. No airlock equals no DuPont stall. So did you have a proof where not dancing equaled a stall and dancing did not. If not you have no idea how to identify an independent variable and are simply repeating an idea you can’t prove

To be honest I find it shocking how close minded you are on this. It obviously works and you don’t know why. Maybe that’s what bothers you.

Bottom line. When brewers use air locks, they get a DuPont stall. The yeast is famous for it. It is the very reason this thread exists. Yet with an open primary, there is no DuPont stall. Whether you can identify why is irrelevant to the fact that it works.

Please, go brew some Saisons with only DuPont yeast and an airlock and see if they stall then try some without an airlock. Then come back with your results.

 

[Vale71]

Bottom line. When brewers use air locks, they get a DuPont stall.

No they don't. Several posters have confirmed that they succesfully brewed with an airlock and have experienced no stalls, yet you choose to ignore their experiences because they clearly go against your magic beliefs.
I think this discussion has gone beyond pointless. I won't contribute anything more except to wonder once again at how gullible people really can be.

 

[Gregory T]

No they don't. Several posters have confirmed that they succesfully brewed with an airlock and have experienced no stalls, yet you choose to ignore their experiences because they clearly go against your magic beliefs.
I think this discussion has gone beyond pointless. I won't contribute anything more except to wonder once again at how gullible people really can be.

Those posters pitched it with a different yeast as well. They did not pitch only DuPont yeast.


Are you afraid of the proofs. Go,ahead brew some saisons. Use ONLY DuPont yeast. Come back and tell us what happened. As of this point
You are right you have not contributed anything

 

[Vale71]

I'm not afraid of any bullcrap you or anybody else might post.
From a scientific standpoint you don't even have a theory. You only have a (questionable) correlation, no valid theory to explain it and certainly no experimental confirmation. You're basically saying that yeast inside a fermenter is able to react to the fact that headspace pressure is at most 2 mbar over the ambient pressure in that location and at that time and will react to this situation by stalling fermentation. Considering that unless DuPont yeast is outfitted with some form of wireless connection and is able to communicate with a local weather station or wireless barometer to determine what the ambient pressure is at this moment this is clearly a feat that is physically impossible I would say your ludricous theory is not even worth discussing further.
Or maybe I'm wrong and you have a verifiable theory on how this could happen, in which case I'd appreciate it if you would let us partake of it. I assure you that I won't try to publish ahead of you and will give you full credit for your breakthtough.

 

[Vale71]

Are you afraid of the proofs. Go,ahead brew some saisons. Use ONLY DuPont yeast. Come back and tell us what happened. As of this point
You are right you have not contributed anything

And this is where you show us that you clearly have no idea about how the scientific method works. You have to prove your assertions using the scientific method, the onus of proof is on you and not on everybody else to prove you wrong. So far you don't even have anything even closely resembling a theory to work on, all you have is "I've done a few beers without airlock and they never stalled", which proves absolutely nothing.

 

[Gregory T]

I'm not afraid of any bullcrap you or anybody else might post.
From a scientific standpoint you don't even have a theory. You only have a (questionable) correlation, no valid theory to explain it and certainly no experimental confirmation. You're basically saying that yeast inside a fermenter is able to react to the fact that headspace pressure is at most 2 mbar over the ambient pressure in that location and at that time and will react to this situation by stalling fermentation. Considering that unless DuPont yeast is outfitted with some form of wireless connection and is able to communicate with a local weather station or wireless barometer to determine what the ambient pressure is at this moment this is clearly a feat that is physically impossible I would say your ludricous theory is not even worth discussing further.
Or maybe I'm wrong and you have a verifiable theory on how this could happen, in which case I'd appreciate it if you would let us partake of it. I assure you that I won't try to publish ahead of you and will give you full credit for your breakthtough.

Here is what I have



Saisons using DuPont yeast have a tendency to stall.

When used without an airlock, they don’t stall

If you knew what scientific method is. We wouldn’t be having this convesation

You think mixing 2 yeasts proves something about whether one stalls? Silly

I don’t have to know they theory of fligh to accept that birds can fly

If you want to know why they don’t stall without an airlock and do stall when they do, I suggest YOU start conducting some controlled experiments

I’m certainly not going to waste my time to try to prove something you will just claim is not real

there is obviously a difference between a closed and an open environment that isn’t simply explained away by discussing atmospheric pressures.

You refuse to accept the experimentation.

You refuse to conduct your own

You just come on here and tell us all how you know no better because you think you’re right

Go ahead brew some saison

What are you afraid of?

To be honest I can’t imagine there is anything to gain by continuing to listen to your bs. #dontfeedthetrolls. Peace out

 

[Gregory T]

When I first started flying I had a new captain on our normal route out of BVT in January. The windshield began to ice up. He said the windshield heat was inop. I explained it had worked all week, but we had used low. He exclaimed forcefully that low wouldn’t be enough. I said, well High isn’t working at all. He absolutely refused to try low. Completely convinced it wouldn’t be enough. Of course it was the 80’s and he was the Captain so he had the authority to kill us both

As we descended to land, the windshield still iced over, He opened the side window and landed the plane with his head out. Scariest thing I’ve seen in 30 years of aviation.

We found out later from Maintenance the high side of the windshield heat had been deactivated. Apparently the plane had flown routes in Hawaii for years and the high was deactivated to prevent damage

The deactivated sticker had either fell off or was never installed

But boy that captain was convinced he was right despite all eveidence to the contrary.

People amaze me

Glad I never had to fly with that fool again

 

[Miraculix]

When I first started flying I had a new captain on our normal route out of BVT in January. The windshield began to ice up. He said the windshield heat was inop. I explained it had worked all week, but we had used low. He exclaimed forcefully that low wouldn’t be enough. I said, well High isn’t working at all. He absolutely refused to try low. Completely convinced it wouldn’t be enough. Of course it was the 80’s and he was the Captain so he had the authority to kill us both

As we descended to land, the windshield still iced over, He opened the side window and landed the plane with his head out. Scariest thing I’ve seen in 30 years of aviation.

We found out later from Maintenance the high side of the windshield heat had been deactivated. Apparently the plane had flown routes in Hawaii for yeast and the high was deactivated to prevent damage

The deactivated sticker had either fell off or was never installed

But boy that captain was convinced he was right despite all eveidence to the contrary.

People amaze me

Glad I never had to fly with that fool again

Good news is, you'll probably never have to argue with this guy above again. Had a similar conversation with him before, he being a similar.... As well, and since then he is completely ignoring me.

I wish him all the best and that he gets his stuff sorted some day.

 

[Qhrumphf]

Actually I've used 100% DuPont (3724 edition) a good few times, with an airlock or a blowoff, and no stall. Every single time I've used pure Dupont it has never stalled, and every time it's had an airlock. I just crank pure Dupont hotter than I do blends.

I said all that already. You read what you wanted.

I don't deny that pressure is a difference.

The impact of pressure on yeast activity is well known. It's why open ferments are typically done in short, squat, often square fermenters. As opposed to mostly vertical conicals.

But scale becomes an issue. Because a yeast cell doesn't change size between a 5 gallon batch and a 120bbl batch. But the hydrostatic pressure certainly does, along with, relatively, much narrower blowoff piping for the batch size and amount of CO2 created.

What the other poster is pointing out, validly, is that the the pressure difference between airlock and no airlock is minimal at best and easily overshadowed by other factors.

That doesn't mean there's not something else going on. It means it may not be pressure at this scale.

You're creating a correlation you have nothing but anecdote to support. It doesn't mean you're wrong about the result. Anecdote is still evidence, albeit weak evidence. It means more research is needed. But scientific knowns about pressure are stronger, and suggest that, at homebrew scale, pressure is NOT the factor. Another poster suggested oxygen access, which makes far more sense.

But, you CAN use pure Dupont with an airlock and not stall.

 

[couchsending]

I’ve used 3724 by itself once

I used yeast nutrient
Pitched a healthy amount of yeast at high krausen
Fermented it at 80-85+ controlled
Didn’t use an airlock

It stalled...

 

[Vale71]

Didn’t use an airlock

It stalled...

No way! Panic in the streets. The world is coming to and end!

 

[Qhrumphf]

Shame I don't have the gear, sounds like an experiment.

Identical three way split. For science. Only variable change-

1. Normal closed ferment (control)
2. Open ferment
3. Normal closed ferment with additional pure O2 added at 24 hrs.

My hypothesis is if #2 outperforms #1, #3 will outperform them both.

 

[suregork]

This is a bit off-topic, but this here is a prime example of how our findings in this recent preprint ( https://www.biorxiv.org/content/10.1101/654681v1 ) can explain some of the scenarios homebrewers encounter with saison strains (I started a separate thread a couple of weeks ago with the main results: https://www.homebrewtalk.com/forum/threads/solving-the-mysteries-of-diastatic-brewing-yeast.666744/ ). The main finding in our study was that many saison strains (i.e. those with the STA1 gene) have a deletion in the promoter of the STA1 gene. In simple words, many strains with the STA1 gene have a mutation that decreases the amount of enzyme produced.

We haven't tested WY3724, but based on everyone's experiences with it (i.e. it easily gets stuck, doesn't superattenuate easily) we can assume that this is a strain with a deletion in the STA1 promoter. We did test WLP565, and that strain had a deletion in the STA1 promoter. Another finding in the study, was that the saison strains (i.e. those that belong to the Beer2 clade) use the STA1 glucoamylase as the main mechanism for maltotriose use, and having the deletion in the promoter significantly decreases production of this glucoamylase and hence maltotriose use.

In practice, this means that when people use this strain and fermentation seems stuck, you most likely are in a situation where the yeast has consumed all the maltose and glucose from the wort and most of the maltotriose remains (this is usually around 1.018-1.024 in a 1.060 wort). The STA1 enzyme is still produced at very low levels in strains with the deletion, so with time the yeast might consume most of the maltotriose. The main factor that encourages production of the STA1 enzyme in strains with the deletion is oxygen. So this could be one of the reasons that people have reported better attenuation with open fermentations. Adding another yeast late is fermentation might not work, since the wort contains almost exclusively the complex malt sugars at that point (but can always be tried).

 

[Gregory T]

Actually I've used 100% DuPont (3724 edition) a good few times, with an airlock or a blowoff, and no stall. Every single time I've used pure Dupont it has never stalled, and every time it's had an airlock. I just crank pure Dupont hotter than I do blends.

I said all that already. You read what you wanted.

I don't deny that pressure is a difference.

The impact of pressure on yeast activity is well known. It's why open ferments are typically done in short, squat, often square fermenters. As opposed to mostly vertical conicals.

But scale becomes an issue. Because a yeast cell doesn't change size between a 5 gallon batch and a 120bbl batch. But the hydrostatic pressure certainly does, along with, relatively, much narrower blowoff piping for the batch size and amount of CO2 created.

What the other poster is pointing out, validly, is that the the pressure difference between airlock and no airlock is minimal at best and easily overshadowed by other factors.

That doesn't mean there's not something else going on. It means it may not be pressure at this scale.

You're creating a correlation you have nothing but anecdote to support. It doesn't mean you're wrong about the result. Anecdote is still evidence, albeit weak evidence. It means more research is needed. But scientific knowns about pressure are stronger, and suggest that, at homebrew scale, pressure is NOT the factor. Another poster suggested oxygen access, which makes far more sense.

But, you CAN use pure Dupont with an airlock and not stall.

I’m not saying it’s pressure. I don’t know why it doesn’t stall in an open primary. I frankly don’t care. I know that it works

It could be psi. It could be dissolved CO2. It could be that when it’s open some wild 3711 finds its way in. It could be something else entirely

What I do know is that when I brew a Saison with DuPont yeast and leave it open for 8 days. It reaches final gravity

That isn’t speculative

The only other person I’ve read that didn’t get a stall was removing their lid and checking gravity daily, hence removing pressure/allowing CO2 out/allowing wild 3711 in/ or whatever reason that it works

But hey if the DuPont stall is a myth then you should recommend the OP does not need to do anything. Take gravity measurements weekly and let us know how it goes.

Of course you said you raised temperature didn’t you? Well have to not to that

I mean it could be an either or thing. Use an airlock and raise temperature or leave temperature and don’t use an airlock

I mean not that long ago no one knew yeast existed. They still made beer

 

[Gregory T]

Now that I think about it and I’m no chemist. Maybe it’s dissoved CO2. Leaving the airlock with off would lower that and so would increasing the temperature

 

[Miraculix]

This is a bit off-topic, but this here is a prime example of how our findings in this recent preprint ( https://www.biorxiv.org/content/10.1101/654681v1 ) can explain some of the scenarios homebrewers encounter with saison strains (I started a separate thread a couple of weeks ago with the main results: https://www.homebrewtalk.com/forum/threads/solving-the-mysteries-of-diastatic-brewing-yeast.666744/ ). The main finding in our study was that many saison strains (i.e. those with the STA1 gene) have a deletion in the promoter of the STA1 gene. In simple words, many strains with the STA1 gene have a mutation that decreases the amount of enzyme produced.

We haven't tested WY3724, but based on everyone's experiences with it (i.e. it easily gets stuck, doesn't superattenuate easily) we can assume that this is a strain with a deletion in the STA1 promoter. We did test WLP565, and that strain had a deletion in the STA1 promoter. Another finding in the study, was that the saison strains (i.e. those that belong to the Beer2 clade) use the STA1 glucoamylase as the main mechanism for maltotriose use, and having the deletion in the promoter significantly decreases production of this glucoamylase and hence maltotriose use.

In practice, this means that when people use this strain and fermentation seems stuck, you most likely are in a situation where the yeast has consumed all the maltose and glucose from the wort and most of the maltotriose remains (this is usually around 1.018-1.024 in a 1.060 wort). The STA1 enzyme is still produced at very low levels in strains with the deletion, so with time the yeast might consume most of the maltotriose. The main factor that encourages production of the STA1 enzyme in strains with the deletion is oxygen. So this could be one of the reasons that people have reported better attenuation with open fermentations. Adding another yeast late is fermentation might not work, since the wort contains almost exclusively the complex malt sugars at that point (but can always be tried).

Thanks very much for the insight, that pretty much confirms my hypothesis above

 

[Qhrumphf]

I mean it could be an either or thing. Use an airlock and raise temperature or leave temperature and don’t use an airlock

That does seem to be the options, yes. Trying it cooler and open has been on the list for years but haven't gotten around to it.

And in fairness, your first post in this thread attributed it to backpressure as per the link you posted.

 

[Vale71]

Leaving the airlock with off would lower that and so would increasing the temperature

No it won't, at least not until primary fermentation is finished. The reason being the rate at which CO2 is produced by yest far exceeds the rate at which CO2 can escape. Once fermentation is finished then of course the CO2 content will diminish as CO2 diffuses out of the beer and is no longer replaced by newly produced CO2. Which is one of the reasons why in commercial operations that still practice "open fermentation" beer is transferred to maturation vessels before FG is reached (for spunding purposes).
To claim that this is the cause for fermentation not stalling is absurd as the reduction would only happen once fermentation stops, so that the cause would follow its own effect which is patently absurd. In a sicientific context of course, in a magical interpretation all bets are off...

Edited to add: in all fairness there will be a negligible difference not attributable to CO2 escaping without an airlock versus CO2 not escaping with an airlock as the latter is obviouly false. CO2 escapes with an airlock too, as proven by the airlock itself bubbling happily. The only difference is again attributable only to the slightly elevated headspace pressure, so we are back again to the 1-2 mbar increase in pressure which will induce an increase in CO2 content of a few ppm at best and that's totally negligible over a normal content of 2-3 parts per thousand, dependent on fermentation temperature.

 

[Qhrumphf]

No it won't, at least not until primary fermentation is finished. The reason being the rate at which CO2 is produced by yest far exceeds the rate at which CO2 can escape. Once fermentation is finished then of course the CO2 content will diminish as CO2 diffuses out of the beer and is no longer replaced by newly produced CO2. Which is one of the reasons why in commercial operations that still practice "open fermentation" beer is transferred to maturation vessels before FG is reached (for spunding purposes).
To claim that this is the cause for fermentation not stalling is absurd as the reduction would only happen once fermentation stops, so that the cause would follow its own effect which is patently absurd. In a sicientific context of course, in a magical interpretation all bets are off...

Edited to add: in all fairness there will be a negligible difference not attributable to CO2 escaping without an airlock versus CO2 not escaping with an airlock as the latter is obviouly false. CO2 escapes with an airlock too, as proven by the airlock itself bubbling happily. The only difference is again attributable only to the slightly elevated headspace pressure, so we are back again to the 1-2 mbar increase in pressure which will induce an increase in CO2 content of a few ppm at best and that's totally negligible over a normal content of 2-3 parts per thousands, dependent on fermentation temperature.

And we're back to....oxygen access.

Which suregork very much seemed to validate.

I wish I had access to my old pilot system where I could set it up for a closed O2 injection. Because I'm legit curious about a second oxygenation regimen and what impact it'd have.

I can't close it enough when adding O2 at home to make it valid enough for my standards.