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Carbonation (Henry's Law) question

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Kaiser:

--- Quote from: hubie on March 21, 2013, 06:00:28 AM ---
That is the part about Henry's Law that I'm not sure about.  Since my chest freezer is holding CO2 in, let's assume that when the beer cools back down and when it sucks gas back through the airlock that it is all CO2 coming back in.  The part I was wondering about is after the beer warms up and loses CO2, when it cools back to its original temperature does it pick up the same amount of CO2 that it lost, or is it a lower amount because the beer was originally sitting in a supersaturated state?  Since the CO2 partial pressure is the same before and after in this example, I suppose Henry's Law says that it would eventually take up the same amount of CO2.

--- End quote ---

I don’t think that your chest freezer is filled with 100% CO2. CO2 and air diffuse fairly quickly, otherwise we would not see a difference between yeast growth in an airlocked starter and one covered with foil. But there is much more CO2 in your chest freezer than there is in air.

If the headspace is 100% CO2 than a warmed up and cooled down beer will have the same CO2 level than a beer that remained at the same temp. This assumes that equilibrium was reached. How long it takes to reach that equilibrium, I don’t know. I think we are talking on the order of a few days here.


--- Quote ---I guess another way of looking at it is, say I have two beers that have just finished fermenting.  One I leave undisturbed and the other I use a wine whip and degas as much CO2 out of it that I can.  If I let them both sit under the same amount of CO2 headspace pressure, do they eventually end up with the same amount of dissolved CO2, or does the undisturbed one hold more because it started from a supersaturated state?

--- End quote ---

A supersaturated liquid will move towards equilibrium once the production of CO2 stops. Both beers will eventually end up with the same amount of dissolved CO2

Jimmy K:

--- Quote from: hubie on March 21, 2013, 06:00:28 AM ---I guess another way of looking at it is, say I have two beers that have just finished fermenting.  One I leave undisturbed and the other I use a wine whip and degas as much CO2 out of it that I can.  If I let them both sit under the same amount of CO2 headspace pressure, do they eventually end up with the same amount of dissolved CO2, or does the undisturbed one hold more because it started from a supersaturated state?

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I don't think Henry's law would ever get you back to a supersaturated state. Also, eventually may be very long if the beer sits undisturbed. CO2 will dissolve into the surface layer, but without mixing it kind of stops. At least, this is what happens in lakes - only a few different system variables there. But the idea is the same as temperature gradients around an immersion chiller.
 
A few years back I read a thread on another forum. The person had calculated the CO2 contribution from an ounce of priming sugar and showed that the priming sugar and dissolved CO2 along were not enough to provide the volumes of CO2 predicted by those charts. The rest must come from supersaturation and/or small amounts of continued fermentation.

euge:

--- Quote ---In physics, Henry's law is one of the gas laws formulated by William Henry in 1803. It states:

    "At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid."
--- End quote ---

I think for any meaningful and immediate effects one needs to vary significantly from the standard atm in your brewery and will require a pressure vessel. Movement in an airlock IMO is not indicative of a large pressure change of any significant value. I would go from the highest temp if you let your beer warm up in a fermenter and then chilled it again, based on your scenario.

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