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Old 05-19-2012, 03:32 AM   #1
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Default 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?

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Old 05-19-2012, 03:45 AM   #2
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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????

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Old 05-19-2012, 03:49 AM   #3
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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.

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Old 05-19-2012, 03:56 AM   #4
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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

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Old 05-19-2012, 05:03 AM   #5
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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.

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Old 05-19-2012, 05:16 AM   #6
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Quote:
Originally Posted by ajdelange View Post
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.
ouch... now my head hurts. easy answer? yep. airlocks work for 200,000 homebrewers
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Old 05-19-2012, 05:22 AM   #7
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An airlock isn't really airtight, but then again, neither is the space station. They're both, however, close enough for what you need.

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Old 05-19-2012, 05:28 AM   #8
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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.

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Old 05-19-2012, 06:04 AM   #9
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Quote:
Originally Posted by daksin View Post
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.
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...
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Old 05-19-2012, 06:41 AM   #10
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I went to school with Brown, he was a real doucher. I wouldn't listen to anything he said.

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