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Old 12-20-2012, 01:07 PM   #381
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Originally Posted by TheKeggingPart View Post
but over a long enough time period, diffusion should cause homogeneity.
Disclaimer: I'm not a scientist. This seems counterintuitive. Why wouldn't gases of different densities stratify, as liquids do? If they wouldn't stratify then, indeed, I need to rethink the "protective layer".

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Old 12-20-2012, 01:12 PM   #382
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Quote:
Originally Posted by Pilgarlic

Disclaimer: I'm not a scientist. This seems counterintuitive. Why would gases of different densities stratify, as liquids do? If they wouldn't stratify then, indeed, I need to rethink the "protective layer".

Thanks.
It's really more of a purge than a 'protective snugly blanket' of CO2. When co2 outgases it pushes all the other air (nitrogen/oxygen) out.

When you blast the headspace with CO2 you are purging, and then IF the Carboy is still enough it might stratify but I really doubt it. It's the purging of air that counts.

I am a scientist. But Not an atmospheric one. We 'lay down a blanket' with argon gas. But that is quite a bit more dense than CO2
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Old 12-20-2012, 01:34 PM   #383
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It's really more of a purge than a 'protective snugly blanket' of CO2. When co2 outgases it pushes all the other air (nitrogen/oxygen) out.

When you blast the headspace with CO2 you are purging, and then IF the Carboy is still enough it might stratify but I really doubt it. It's the purging of air that counts.

I am a scientist. But Not an atmospheric one. We 'lay down a blanket' with argon gas. But that is quite a bit more dense than CO2
If true, then lots of people are getting a false sense of security from the "C02 is heavier" maxim.
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Old 12-20-2012, 01:53 PM   #384
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if you have two gasses mixed, they won't stratify, at least not in brewing time scales. gravity pulls the heavier ones more, but the forces of molecular collisions make it difficult for this slight difference to have a huge effect.
just like if you have a solution of sugar in water, the sugar won't accumulate towards the bottom. some can crystalize out of solution, but that's different from the liquid stratifying. that's the difference between a solution and a suspension; in a solution the individual molecules form a contiguous matrix with the solvent. in a suspension there are clumps of things; sand particles, yeast, that are held up by the liquid but not dissociated into molecules. suspensions stratify quite readily. big particles in gas, like smog, can also easily stratify.
so if you layer a less dense solution on top of a more dense one, and don't mix, it can remain stratified; just like those underwater caves where fresh water that has trickled through the rock overlies salt water from the sea. it can work the same for gasses, if you don't mix them they can remain stratified, like in a pyroclastic flow; think pliny and vesuvius, but if you mix them, the heavier gas is not going to miraculously separate to the bottom. there are probably cases where this can happen, but for practical purposes of co2 and air in a fermenter, i stake my flimsy reputation on the idea that they won't spontaneously stratify, but can display stratification if co2 is evolving off from the beer, or added as pure co2 that isn't yet mixed with air!

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Old 12-20-2012, 01:56 PM   #385
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So the accepted norm is to purge with CO2 then?

This may seem like a silly question, but such are the advantages of semi-anonymity. I have a CO2 tank that I use for kegging, but the only adapters I have are fitted for ball-lock kegs. Do people just keep a separate hose with no adapter at the end for purging?

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Old 12-20-2012, 02:11 PM   #386
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I agree that you won't get stratification in any reasonable brew time. I'm not sure that I agree that the relatively small amount of air introduced while taking a sample will mix with the existing CO2 'blanket' and form a homogenious solution that will lead to the oxidization of the beer. Unless you're swirling the sampling wand around or you have to remove a large lid off a bucket that will create mixing due to pressure differentials, I would wager that you'd be hard pressed to notice any sort of oxidization associated with the sampling of your beer.

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Old 12-20-2012, 02:11 PM   #387
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Do people just keep a separate hose with no adapter at the end for purging?
Yes. And I use one of these for good measure.
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Old 12-20-2012, 06:10 PM   #388
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Once the gasses are mixed they won't stratify in any length of time.

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Old 12-21-2012, 03:46 PM   #389
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I really like this conversation and need to ask the question of flavor. I think we can all agree that the yeasts that we use contribute to the flavor of our beer. It seems as though we can control those flavors by how much time the yeast sits in contact with the beer in primary, at least in my belief. One of the beers I brew absolutely needs to stay in primary for over 2 weeks in order to develop the flavor that I am shooting for. Anything less that 10 days and it does not take on the specific flavor that I want from the yeast. But for all my other beers, once the yeast has done its job, I rack to secondary for it to "age" or condition for at least a week, usually two weeks. Sometimes, beer left to long in primary can turn out to be way too "yeastie", so to speak.

My question would be, if you do leave the beer in primary for a month, how would the flavors of the beer be affected by this? Also, are there certain yeasts that do better or worse than others in regards to flavor? Its hard to believe that all yeasts will do great with beer on it for a month. There has to be certain yeasts or beer styles that do better in this environment that others, but hey, I could be wrong.

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Old 12-22-2012, 03:45 PM   #390
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A visit to youtube shows us quite graphically how heavy CO2 is.

http://youtu.be/Xzfq3lIWu9s
http://youtu.be/g3PZwPSz2n4
Based on these I'm inclined to think that it does indeed form a protective layer over our beer.

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