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dave_witt
08-27-2013, 07:36 PM
Hey guys. I have an odd question and I'm not sure of the best place to put it. Anyways, I removed the airlock on a 3 gallon carboy that is at 70 or 72 degrees. I blanketed the mead with CO2 at about 50 degrees and replaced the airlock. It apparently created a vacuum, which seems odd to me given that the gas should be expanding and pushing out of the airlock. Does anyone have an explanation for this, and perhaps even some advice as to how I should proceed?

mannye
08-27-2013, 08:29 PM
Seems the gas is still at 50 degrees and you've got negative pressure. It should warm up and push back out. ::takes another swig of giggle honey::

Chevette Girl
08-27-2013, 08:47 PM
Yep, I'm, stumped too. Should be expanding, since at 50f it should be denser than at 70f... Weird.

joemirando
08-27-2013, 08:49 PM
Yep, I'm, stumped too. Should be expanding, since at 50f it should be denser than at 70f... Weird.


I GUESS it could be possible that the CO2 cooled the mead, which contracted more than the CO2 expanded, but it doesn't seem likely. Just the differences in mass would seem to rule that out, but its the only thing I can come up with. Phase transitions are weird and wonderful things.


Joe

dave_witt
08-27-2013, 08:49 PM
Hopefully that's the case. I'm pretty sure I filled the headspace with CO2 so I'm not sure how it could have negative pressure, no matter what the temperature of the gas, but you're explanation makes more sense than anything else I can think of.

dave_witt
08-27-2013, 09:15 PM
Yeah, I just replaced the airlock, letting the pressure equalize, and things returned to their previously stable condition. I'm assuming that there's still enough of a CO2 blanket in the headspace, that I don't need to worry too much about oxygenating the mead between tonight and tomorrow (and given the fact that I let the airlock dry out for gods know how long).

kuri
08-27-2013, 09:56 PM
One possible explanation is that some of the CO2 dissolved into the mead. In general gasses dissolve better into liquids at lower temperatures. That's usually lower temperature of the liquid, not the gas, but it's possible that the gas cooled the surface of the liquid by a fraction of a degree. More likely, if the air above the mead prior to adding the CO2 had a lower CO2 concentration, then the equilibrium would have been shifted by changing it to pure CO2, and more CO2 would then be absorbed. Can't say I've ever experienced this myself, nor would I have expected it. And I'm not giving this as the truth, only as the only possibility I can see at the moment.

Chevette Girl
08-29-2013, 07:29 AM
I GUESS it could be possible that the CO2 cooled the mead, which contracted more than the CO2 expanded, but it doesn't seem likely. Just the differences in mass would seem to rule that out, but its the only thing I can come up with. Phase transitions are weird and wonderful things.


I'd considered that, but as the must came back to temp it would expand again and push out the airlock... and gas expands at a pretty ridiculous rate... so the only other explanation would be a temperature drop shortly after adding the CO2...

anir dendroica
09-06-2013, 01:25 PM
This is the most likely explanation. I work in a lab that uses dissolved gases as standards, and I have seen this before. CO2 is much more soluble in water than any other common gas. With oxygen or nitrogen, the concentration of dissolved gas relative to gas in the headspace is 1-4%, while with CO2 this ratio is 83%. In practical terms, this means that when you add CO2 to a closed chamber with water, it will draw a vacuum, and you won't see this effect with air.



One possible explanation is that some of the CO2 dissolved into the mead. In general gasses dissolve better into liquids at lower temperatures. That's usually lower temperature of the liquid, not the gas, but it's possible that the gas cooled the surface of the liquid by a fraction of a degree. More likely, if the air above the mead prior to adding the CO2 had a lower CO2 concentration, then the equilibrium would have been shifted by changing it to pure CO2, and more CO2 would then be absorbed. Can't say I've ever experienced this myself, nor would I have expected it. And I'm not giving this as the truth, only as the only possibility I can see at the moment.

Chevette Girl
09-06-2013, 05:39 PM
Well, thank you so much for explaining that! I only know/remember enough about gas to liquid mass transfers to drive myself nutz wondering how that happened! :D

anir dendroica
09-06-2013, 06:02 PM
It's still a bit mysterious though because the mead should be nearly 100% saturated with dissolved CO2 following fermentation. In that case blanketing with CO2 at atmospheric pressure should not lead to further CO2 dissolving. Of course racking into an air-filled carboy (especially with splashing) will cause some of the dissolved CO2 to be lost, which could then create a vacuum if the headspace is purged with 100% CO2.


Well, thank you so much for explaining that! I only know/remember enough about gas to liquid mass transfers to drive myself nutz wondering how that happened! :D