Is an air lock really an air lock?

It seems to me that once fermentation stops, the solvation of atmospheric gasses combined with Brownian motion would allow oxygen to slowly enter over time, making an airlock inferior to a balloon which self seals once fermentation has completed.

Thoughts?

The time that takes is longer than the time my beer stays in fermentor. Plus even when no activity is noticed in the air lock does not mean activity has ceased in the fermenting chamber.

thought????

Balloon's aren't necessarily oxygen impermeable, in fact as pressure in the balloon builds, I'd imagine the barrier becomes more permeable. The rate of oxygen dissolution into water and then back out again would be significantly lower than the passage of oxygen through the walls of a balloon or plastic fermentor, particularly given the differences in area.

sounds like an engineer question, and i'm not an engineer, but here's what i think. as the beer ferments, it creates a positive layer of pressure over it of co2. it forces all the o2 out, and as the pressure reduces, the co2 spreads a little, creating a fairly high pressure layer throughout the fermenter, all the way up to the airlock. this increased pressure on the (vodka, in my case, in the airlock) keeps o2 out. only if the extra co2 was bled out, which should not happen under any circumstances, would the pressure be reduced enough for 02 to bleed in

The system looks like this:

atmosphere|water|headspace|beer

with | representing an interface between phases. There is a chemical potential difference across each interface which depends on the differences in activity of oxygen in each phase. If a phase contains no oxygen then its chemical potential is infinitely less than an adjacent phase which contains any oxygen and oxygen will, if the interface is permeable to it, pass into the phase at lower potential. Thus an airlock full of water does not prevent the migration of oxygen from the atmosphere into the water, from the water into the headspace and from the headspace into the beer. At equilibrium the amounts of oxygen in each phase will be the amounts required to zero the potential across the interfaces. The beer will contain approximately 8 mg/L oxygen. The saving grace is that it takes a long time for equilibrium to be reached. Provided the beer is only in the carboy for a couple of weeks the amount of oxygen reaching the beer will be very small.

ajdelange said:

The system looks like this:

atmosphere|water|headspace|beer

with | representing an interface between phases. There is a chemical potential difference across each interface which depends on the differences in activity of oxygen in each phase. If a phase contains no oxygen then its chemical potential is infinitely less than an adjacent phase which contains any oxygen and oxygen will, if the interface is permeable to it, pass into the phase at lower potential. Thus an airlock full of water does not prevent the migration of oxygen from the atmosphere into the water, from the water into the headspace and from the headspace into the beer. At equilibrium the amounts of oxygen in each phase will be the amounts required to zero the potential across the interfaces. The beer will contain approximately 8 mg/L oxygen. The saving grace is that it takes a long time for equilibrium to be reached. Provided the beer is only in the carboy for a couple of weeks the amount of oxygen reaching the beer will be very small.

Click to expand...

ouch... now my head hurts. easy answer? yep. airlocks work for 200,000 homebrewers

An airlock isn't really airtight, but then again, neither is the space station. They're both, however, close enough for what you need.

Think about it: Locks don't keep criminals out. Locks just make it harder for criminals to get in.

Now, replace locks with airlocks and criminals with oxygen.

daksin said:

Balloon's aren't necessarily oxygen impermeable, in fact as pressure in the balloon builds, I'd imagine the barrier becomes more permeable. The rate of oxygen dissolution into water and then back out again would be significantly lower than the passage of oxygen through the walls of a balloon or plastic fermentor, particularly given the differences in area.

Click to expand...

True, as pressure builds the balloon would become more permeable. However, the co2 coming off the must will be forcing CO2 gas upward, overcoming any and all Brownian motion and forcing the O2 back out.


I've read the other answers and have to agree...

I went to school with Brown, he was a real *****er. I wouldn't listen to anything he said.

You realize that they used to make high quality beer using open fermentation, no airlocks. The oxygen that can permeate into you beer post fermentation is so small you'll never know its there. No need to worry about this at all

KuntzBrewing said:

You realize that they used to make high quality beer using open fermentation, no airlocks. The oxygen that can permeate into you beer post fermentation is so small you'll never know its there. No need to worry about this at all

Click to expand...

Who said I was worried? It's just the discussion I was interested in.

KuntzBrewing said:

The oxygen that can permeate into you beer post fermentation is so small you'll never know its there. No need to worry about this at all

Click to expand...

The oxygen that can permeate into your beer post fermentation is enough to ruin it pretty quickly if you aren't very careful. Advanced home brewers and commercial brewers go to incredible lengths to prevent oxygen from contacting their finished beer. If the beer is to be consumed within a few weeks of packaging you can get away with some oxygen contamination. If a shelf life of months is desired then great care (counter pressure filling, capping on foam...) is required.

KuntzBrewing said:

You realize that they used to make high quality beer using open fermentation, no airlocks. The oxygen that can permeate into you beer post fermentation is so small you'll never know its there. No need to worry about this at all

Click to expand...

They still make high quality beer using open fermentation. New Glarus in Wisconsin has some open fermenters. Really cool stuff.

ajdelange said:

The oxygen that can permeate into your beer post fermentation is enough to ruin it pretty quickly if you aren't very careful. Advanced home brewers and commercial brewers go to incredible lengths to prevent oxygen from contacting their finished beer. If the beer is to be consumed within a few weeks of packaging you can get away with some oxygen contamination. If a shelf life of months is desired then great care (counter pressure filling, capping on foam...) is required.

Click to expand...

What? I have been transferring my beers from my fermenters to my bottling bucket with no top on it. It is also filled with air when the beer goes in there. All my beers have been ruined! Damn!

Do I really have to drink all 500+ bottles I have in the next few weeks?

kh54s10 said:

Do I really have to drink all 500+ bottles I have in the next few weeks?

Click to expand...

That depends on your tolerance for stale beer. Given that you bottle the way you do it's clear that you are either unaware of the problem or don't care. Neither case suggests that you need to drink the beer up quickly. You might consider taking BJCP beer judge training. This will help you identify staling and other off flavors, show you what you can do about it, might be a lot of fun for you and will potentially add another judge to the pool. They are needed.

ajdelange said:

That depends on your tolerance for stale beer. Given that you bottle the way you do it's clear that you are either unaware of the problem or don't care. Neither case suggests that you need to drink the beer up quickly. You might consider taking BJCP beer judge training. This will help you identify staling and other off flavors, show you what you can do about it, might be a lot of fun for you and will potentially add another judge to the pool. They are needed.

Click to expand...

I am under the impression that most people bottle with essentially the same method I use.

My beers turn out great and that is not just my opinion. I may have some off flavors but I'm sure they have other sources also.

IMO unless introducing oxygen by splashing etc., it is relatively difficult to ruin a beer during bottling.

kh54s10 said:

My beers turn out great and that is not just my opinion.

Click to expand...

You may be able to produce an acceptable beer allowing exposure to oxygen but you will not produce a great one. Cold side aeration must be controlled to produce a great beer. Were this not so the commercial people would not spend the money they do to keep airs down to very low levels nor would they waste money on things like Orbisphere meters to see how well their bottling lines do in this regard.

I suggested the BJCP program as a means of educating your palate about the effect of staling. You will taste fresh and stale beers and after doing that you will know how much better your beer could potentially be if you protected it from air on the cold side. I bottled as you do in the early phases of my brewing career and though that my beers were pretty good (and some of them were before staling set in). But now that I understand the science better and have improved my packaging practices I am able to drink 'fresh' Pils for up to a year and perhaps a bit more after kegging.

kh54s10 said:

IMO unless introducing oxygen by splashing etc., it is relatively difficult to ruin a beer during bottling.

Click to expand...

There is an entire industry and a legion of home brewers that do not share that opinion. Perhaps 'ruin' is too strong a word but oxidized flavors are not pleasant to me unless it is in a style that depends on it (Barley wine) for part of its character.

You know I'm a real novice so take this with a grain of salt but I always thought that airlocks were more to reduce the potential of airborne contaminants getting into the beer while still allowing for pressure relief during fermentation. Co2 is about twice as heavy as o2 so I would figure that with a lid and airlock reducing air movement to almost none that the co2 in the fermenter would pretty effectively displace any o2 above the wort/beers surface sort of like argon does in an uncorked bottle of wine.

Thoughts?

ajdelange said:

That depends on your tolerance for stale beer. Given that you bottle the way you do it's clear that you are either unaware of the problem or don't care. Neither case suggests that you need to drink the beer up quickly. You might consider taking BJCP beer judge training. This will help you identify staling and other off flavors, show you what you can do about it, might be a lot of fun for you and will potentially add another judge to the pool. They are needed.

Click to expand...

Wow are you a diplomat?
If not you should be.

DerCribben said:

You know I'm a real novice so take this with a grain of salt but I always thought that airlocks were more to reduce the potential of airborne contaminants getting into the beer while still allowing for pressure relief during fermentation.

Click to expand...

That's true.

DerCribben said:

Co2 is about twice as heavy as o2 so I would figure that with a lid and airlock reducing air movement to almost none that the co2 in the fermenter would pretty effectively displace any o2 above the wort/beers surface sort of like argon does in an uncorked bottle of wine.

Click to expand...

Removal of oxygen really depends on the evolving CO2 'sweeping' out the oxygen. In a truly static situation oxygen molecules will wend their way between the CO2 molecules in order to equalize the chemical potential of oxygen as explained above. At the pressures and temperatures we are speaking of the oxygen and CO2 are, to good approximation 'ideal gasses'. That means the carbon dioxide is unaffected by the oxygen and conversely i.e. the fact that CO2 is heavier does not mean it displaces oxygen AT EQUILIBRIUM.

If you pour water into oil the water will go straight to the bottom and stay there because
1. Water is heavier than oil
2. Water and oil are immiscible

If you pour ethanol into water this separation will not occur even though water is heavier than ethanol. The reason is that the two are miscible - ethanol molecules can slip between water molecules and conversely. This is more like the case of two nearly ideal gasses.
[/QUOTE]

ajdelange said:

You may be able to produce an acceptable beer allowing exposure to oxygen but you will not produce a great one. Cold side aeration must be controlled to produce a great beer. Were this not so the commercial people would not spend the money they do to keep airs down to very low levels nor would they waste money on things like Orbisphere meters to see how well their bottling lines do in this regard.

I suggested the BJCP program as a means of educating your palate about the effect of staling. You will taste fresh and stale beers and after doing that you will know how much better your beer could potentially be if you protected it from air on the cold side. I bottled as you do in the early phases of my brewing career and though that my beers were pretty good (and some of them were before staling set in). But now that I understand the science better and have improved my packaging practices I am able to drink 'fresh' Pils for up to a year and perhaps a bit more after kegging.




There is an entire industry and a legion of home brewers that do not share that opinion. Perhaps 'ruin' is too strong a word but oxidized flavors are not pleasant to me unless it is in a style that depends on it (Barley wine) for part of its character.

Click to expand...

Without kegging, no funds for that yet, how do you propose adding the priming sugar and bottling without exposing the beer to air?

I agree that zero exposure to air is better, but again IMO you really have to do something drastic to totally stale a beer during bottling.

Counter pressure transfer by means of carbon dioxide pressure is workable with carboys but you must be very careful to use extremely low pressure as you can fracture a carboy if you aren't careful. Besides which, of course, the CO2 equipment represents a step along the path towards kegging in terms of having to buy gear.

Some advocate letting the primed bottles sit for an hour or so before capping in order to allow the yeast to start fermenting the priming sugar thus producing CO2 which will sweep the air out. If you do that I'd want to put a piece of aluminum foil or something over the necks to keep anything from falling in during that hour.

I'm not thinking clearly this morning. Air exclusion does not need to be so strictly observed if the beer is being carbonated by fermentation of priming sugar as it does when the beer is carbonated at filling (no yeast added). The yeast themselves are great scavengers of oxygen. I guess I would try the method where you let the bottles sit were I to go back to bottle priming. The last time I did that was with Weizen which has to be drunk quickly in any case.

ajdelange said:

The oxygen that can permeate into your beer post fermentation is enough to ruin it pretty quickly if you aren't very careful. Advanced home brewers and commercial brewers go to incredible lengths to prevent oxygen from contacting their finished beer. If the beer is to be consumed within a few weeks of packaging you can get away with some oxygen contamination. If a shelf life of months is desired then great care (counter pressure filling, capping on foam...) is required.

Click to expand...

kh54s10 said:

IMO unless introducing oxygen by splashing etc., it is relatively difficult to ruin a beer during bottling.

Click to expand...

I was a winemaker before making beer, and winemakers take great care to avoid oxidation- topping up fermenters and keeping a very small headspace (the width of the bung only), using potassium metabisulfite as an antioxidant, racking extraordinarily carefully, etc.

Many, many times I've commented on the potential for oxidation in beer as well, but I will say that generally the beer is in the fermenter for far less time so the potential for severe oxidation is less.

When judging beer, the most common flaw I've noted (and other judges too) is oxidation. Most of the beers had signs of oxidation. In some cases, it was severe, like the typical "wet cardboard" we discuss. But mostly it was very early oxidation- a hint of astringency on the sides of the tongue, with a hint of staling, or a bit worse with actual "stale" flavors. It's a very common flaw.

Another issue with a large amount of headspace once fermentation slows is the potential for infection- if you notice all of the "is this infected?" threads, NONE of the beers were in a topped up carboy. Instead they were in a carboy, with lots of headspace, or in a bucket. That is another issue, of course, but it is one danger of leaving too much headspace once fermentation ends.

One of the things that has always bugged me in this forum is people saying things like "the co2 blanket will protect your beer" and "it's hard to actually aerate your beer enough to oxidize it". Both have some basis in truth, of course, but neither are totally true. The co2 "blanket" isn't going to hang around forever, and the Ideal Gas Law applies. And it really does not take a ton of aeration to get oxidation in beer. It may not ruin the beer, and the keg might be gone before it tastes too oxidized, but that doesn't mean it wasn't affected at all.

These are all really fantastic posts! See why I asked the question?

The mark of a good forum.

TheKeg81 said:

Now, replace locks with airlocks and criminals with oxygen.

Click to expand...

that would be quite a world. no need for police and a surplus of costumes for halloween. guess what i'm going as? cop? yeah.
wanna play cops and robbers? don't you mean nothing and oxygen? yeah.

that's a world i don't want to live in- give me hardened criminals over air, anyday.