does airlock pressure have a noticeable impact on fermentation?

I've heard brewers mention that the pressure in a fermentation vessel can play a noticeable role in the fermentation of a beer. If I remember correctly, they've mentioned ester and phenol production and other byproducts of the yeast.


My question: does the pressure from an airlock or a blowoff tube have a noticeable effect on a carboy or bucket fermentation?

If so, are there any other options other than open fermentation? I've heard of people using a cheesecloth over a fermenter, but that seems equivalent to an open fermentation, right?

No. You don't need to worry about that. Bazillions of gallons of beer can and have been brewed in vessels with airlocks, both on the homebrew level and commercially. You are waaaaay overblowing something you read somewhere. Especially on a homebrew level, there's no off flavors from airlock pressure.

Your airlock is a valve to release builtup pressure.

You'll find that a lot of these "things that I heard" are often out of context or barely understood by the folks who might repeat them. A lot of stuff might come from issues in commercial breweries, that bears little resemblance to thing that concern us on our tiny scale. Something might be of huge important on the level of hundreds of gallons of beer, but will mean nothing to our little 5 of 10 gallon batches.

From what I've read, the effects you mention only come into play above 5 psi or so. An inch of water is about .04 psi, so unless you submerge your blowoff tube in more than 10 feet of water, you'll be OK.

The amount of top pressure retained with an airlock is soo small it's really a non-issue in terms of preventing ester development. However, a properly maintained open fermentation (cheese cloth with shallow fermenting vessel... ect) can have a substantial impact on how a beer tastes. Many commerical breweries use open fermentation as a means to easily top crop yeast, enhance ester production, release c02 quickly, and for aesthetics.

Thanks everyone.

Revvy, you have this way of sounding rude even if you don't mean it - not sure if you meant it here.

aggieactuary said:

Thanks everyone.

Revvy, you have this way of sounding rude even if you don't mean it - not sure if you meant it here.

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Welcome to HBT! Revvy is the man with giving advice. He wants to help, not discourage or be rude.

I definitely appreciate his advice. I've read plenty of his threads and his responses where I learned something. I just think he's hard on people.

I like to know why. I know I can (and do) stick an airlock on my fermenter and make good beer. But I'm still going to think about the mechanics, functionality and pros and cons of the airlock.

He's the only guy with the patience to spend a fair amount of his time answering the exact same questions over and over again even after years of doing so. If a little impatience occasionally pokes through, I think it's more than understandable... The average person would have gone absolutely crazy by now

aggieactuary said:

But I'm still going to think about the mechanics, functionality and pros and cons of the airlock.

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*facepalm*

Mechanics: Air inside the bucket/carboy is displaced by CO2 from fermentation. This displaced air has to go somewhere so out the easiest path it goes (i.e. your airlock.)

Functionality: Pressure release valve that allows air out but keeps stuff out. That is all.

Pros: Lets air out, keeps gunk out. Also, satisfying "blub blub blub"

Cons: Makes open-fermentation brewers cry


No pressure is allowed to build up inside your bucket/carboy.... because it escapes out your airlock. Built-up pressure in a fermentation vessel that is not rated for pressure results in blown lids.

aggieactuary said:

I definitely appreciate his advice. I've read plenty of his threads and his responses where I learned something. I just think he's hard on people.

I like to know why. I know I can (and do) stick an airlock on my fermenter and make good beer. But I'm still going to think about the mechanics, functionality and pros and cons of the airlock.

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There's only one con to a typical homebrewing airlock, which is a potential for blocking an expanding krausen, and potentially causing the the airlock or cap to pop off with a messy explosion of wort. I've even heard of an instance where the cap wasn't able to pop off and the bucket itself ruptured instead. But all this just drives home the fact that a typical homebrewing fermentor will never even allow enough pressure to impact fermentation. Some stainless conicals are able to withstand a bit more pressure, but if you're using an airlock, the pressure required to push CO2 through the water is so negligible that it can pretty much be considered atmospheric.

Using a blow-off tube (which is just a different type of airlock anyways) for the first few days significantly reduces the likelihood of a fermentor explosion - and the wider, the better.

It's not really the pressure that effects yeast health and ester formation; it's the amount of dissolved CO2 in solution, which is itself affected by the pressure build-up. Around 29 psi, CO2 absorption is doubled, which decreases ester formation by approximately 50%. Around 35 psi of pressure, yeast will begin to die. However, Chris White has stated (on air interviews, can't find in print/publication) that they've measured decreased ester formation in as little as 1-2 psi environment. With regards to a human taste threshold, this is generally not a large factor or something you can pick out.

As has already been said, the pressure differential is negligible with respect to the airlock and a carboy or bucket with generalized yeast strains. However, it can be a factor of consideration on a much larger, professional level. There's lots of discussion about having strains such as the Ringwood yeast benefiting greatly from reduced head pressure.

Not a super recent publication, but some info is found here and more on yeast and ester production here.

Reno_eNVy_446 said:

No pressure is allowed to build up inside your bucket/carboy.... because it escapes out your airlock. Built-up pressure in a fermentation vessel that is not rated for pressure results in blown lids.

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Negligible, like I said, but with a 1" water column in an airlock, a pressure of around 0.036 psi still builds up. Super nitpicky, I know.

Revvy said:

You'll find that a lot of these "things that I heard" are often out of context or barely understood by the folks who might repeat them.

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To say that Chris White and the other scientists who have studied and published information on this topic "barely understands" these things is pretty insulting, if you ask me. I know Chris has talked about pressure build-up and yeast health rather frequently.

I pretty sure Revvy only meant that with respect to airlocks in homebrewing, but of course I can't speak for him.

Thanks PseudoChef. Good info.

Now that I'm thinking about it and with respect to your comments, it seems that the depth of the wort probably creates more or less pressure variation within the wort than the air pressure.

I guess that's why people comment more on the shape of the fermentation vessel.

aggieactuary said:

Thanks PseudoChef. Good info.

Now that I'm thinking about it and with respect to your comments, it seems that the depth of the wort probably creates more or less pressure variation within the wort than the air pressure.

I guess that's why people comment more on the shape of the fermentation vessel.

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Okay, now you lost me dude. Where are people saying that vessel shape has an effect on fermentation? Because it most certainly doesn't.

The only variation you get from vessel shape is whether or not you have a conical that you can dump trub out from underneath the wort/beer.

Reno_eNVy_446 said:

Okay, now you lost me dude. Where are people saying that vessel shape has an effect on fermentation? Because it most certainly doesn't.

The only variation you get from vessel shape is whether or not you have a conical that you can dump trub out from underneath the wort/beer.

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This is very wrong - height:width ratios and even basic fermentor geometry (extreme examples would be conicals vs square fermentors) have quite a tangible effect on fermentation and the resulting beer, to the point that breweries concerned with consistency often find they have to spend a lot of time tweaking their recipes when they upgrade their fermentors.

Reno_eNVy_446 said:

Okay, now you lost me dude. Where are people saying that vessel shape has an effect on fermentation? Because it most certainly doesn't.

The only variation you get from vessel shape is whether or not you have a conical that you can dump trub out from underneath the wort/beer.

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A simple search of "fermentor geometry" would be appropriate before you just spout fallacies.

emjay said:

I pretty sure Revvy only meant that with respect to airlocks in homebrewing, but of course I can't speak for him.

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You can see here that Chris White has said, on the homebrew level, that he prefers aluminum foil over an airlock to decrease the pressure as much as possible and to achieve faster fermentation. Whether or not there is a difference enough to care about, I can't comment. But to insinuate that a scientist who studies yeast extensively and who founded one of the largest yeast companies "barley understands" this, is insulting.

I happened to listen to the Brew Strong podcast on Saisons today. In it, Jamil and Chris White have a discussion about some of the issues in this thread.

As PsedoChef says, White (and Jamil) advocate a loose foil cover instead of an airlock.

Also, one of them says that depth of the fermenter can suppress yeast flavors.

So, from that I can assume that it seems if you want more yeast flavors, perhaps in a Belgian style or an English ale, you might be better off with a shallower fermentation and a loose foil cover (or even open fermentation). If you want a cleaner profile, like an American ale or lager, you may be better off with a deep fermentation and an airlock or blowoff tube.

Now, I'm not saying you can't make fantastic beer still doing the opposite of everything I just said. You can always tweak temperatures and pitching rates to achieve similar effects. I am saying the depth of you wort during fermentation and to a lesser extent capping with an airlock will impact your beer.

It's just something I think that is good to be aware of.

PseudoChef said:

You can see here that Chris White has said, on the homebrew level, that he prefers aluminum foil over an airlock to decrease the pressure as much as possible and to achieve faster fermentation. Whether or not there is a difference enough to care about, I can't comment. But to insinuate that a scientist who studies yeast extensively and who founded one of the largest yeast companies "barley understands" this, is insulting.

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Don't know why I feel obliged to get in the middle of this, but Revvy didn't say that Chris White "barely understands" this issue. He didn't even insinuate that.

Instead, he wrote that people who often repeat things that they heard don't understand the issue or topic that they are repeating to begin with.

That's a HUGE difference.

True, and it seems like "airlock = bad" IS wrong anyways. It's simply a tool. My next beer is a saison and I'll definitely be doing the foil thing now that I've read that, but for something like an American ale that I really want to suppress the esters, I might take it further than a simple airlock and use a 5-gal bucket full of water as a blow-off to really maximize the PSI. Anybody know what kind of PSI that would create? I'm not sure what numbers are needed, but if somebody's willing to do it, figure a cylinder of the following dimensions:

Volume: 1155in³ (0.668ft³)
Height: 14"
Diameter (Average): 10.25"
Mass: 41.7lbs

I wonder how much it would cost me for enough 1/2inch vinyl tubing to run from my ferm freezer in my garage, to the bottom of my pool... what does the math work a 50,000-gal (417,000lbs water) airlock out to? If the bucket wouldn't explode as a result of the pressure needed to expel gas, I'd seriously do a side-by-side experiment: 2-piece airlock vs pool!

Airlock Pressure? Flat no. Thread should stop here.

emjay said:

I wonder how much it would cost me for enough 1/2inch vinyl tubing to run from my ferm freezer in my garage, to the bottom of my pool... what does the math work a 50,000-gal (417,000lbs water) airlock out to? If the bucket wouldn't explode as a result of the pressure needed to expel gas, I'd seriously do a side-by-side experiment: 2-piece airlock vs pool!

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Weight/volume of the water has nothing to do with it. Only the height of the water above.

Pressure=density*gravity*height of liquid

10 ft of water gets you about 4.3 psi. Would be an interesting way to experiment with pressure on fermentation. But, anything other than a well-sealed SS fermenter would leak well shy of 1 psi or explode.

NightTrainLayne said:

Don't know why I feel obliged to get in the middle of this, but Revvy didn't say that Chris White "barely understands" this issue. He didn't even insinuate that.

Instead, he wrote that people who often repeat things that they heard don't understand the issue or topic that they are repeating to begin with.

That's a HUGE difference.

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Fair enough, but if someone is interested in a topic, s/he should be directed toward the information rather than just thrown a "it doesn't matter," when, as I've tried to point out, it might. I just hate seeing people chime in (as I've also pointed out in this thread) with completely incorrect information. If you don't know about the subject or are at least willing to google or read some literature on it, then please don't chime in.

Beerrific said:

Weight/volume of the water has nothing to do with it. Only the height of the water above.

Pressure=density*gravity*height of liquid

10 ft of water gets you about 4.3 psi. Would be an interesting way to experiment with pressure on fermentation. But, anything other than a well-sealed SS fermenter would leak well shy of 1 psi or explode.

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This

From what I've seen, fermentor geometry has only to do with how much the wort churns during fermentation. Not only is that not what we're discussing, but it's also negligible at a homebrew scale considering none of us have fermentation vessels that can have 30-50ft tall liquid columns.