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11-19-2010, 02:57 PM   #21
JLem
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Quote:
 Originally Posted by DarkUncle So are you saying that the beer carbonates first and becomes saturated before any CO2 is expelled into the headspace of the bottle? If that's true than why would it be when I popped open a bottle after a week and a half that a little hiss can be heard, which I would assume to be the release of some CO2, but the beer is still flat? Shouldn't the beer be carbed up at that point if there is now CO2 in the headspace of the bottle?
The yeast produce CO2 which goes into solution. The amount of CO2 that can be held in solution is a function of the temperature of the solution and the pressure - basic gas laws here. As the yeast continue to produce CO2, the solution will reach its saturation point for the current pressure, so some of the CO2 escapes into the headspace. As the CO2 increases in the headspace, because the bottle is capped, the pressure inside the bottle builds up, which increases the amount of CO2 that can go into solution - you can think of the increased headspace pressure literally forcing the CO2 back into solution until the pressure of the CO2 pushing out of solution is equal to the pressure pushing back in - the system maintains equilibrium. At some point all the sugars are used up and no more CO2 is produced. Otherwise, if you add too much sugar, too much CO2 builds up, increasing the pressure inside the bottle until the glass cannot take it any more and explodes (the force of the CO2 inside exceeds the material strength of the glass).

Now, once the yeast are done converting all the sugars into CO2, there will still be CO2 in the headspace. When you then chill the beer down, more CO2 goes into solution since colder liquids can hold more gas. When you pop the top, you've released the pressure, which is the hiss you hear as CO2 escapes. With the pressure released, the beer is now out of equilibrium, so the CO2 dissolved in the beer comes out of solution once more as the system swings back into equilibrium, this time with the lowered ambient pressure. Hence, we get nice bubbles (and foam) when we pour. If you don't have a lot of CO2 dissolved in solution - either because you didn't add enough priming sugar or the yeast haven't had time to fully convert the sugar into CO2, the CO2 in solution quickly dissipates (come out of solution), and the result is flat beer (even though you heard a hiss when you popped the top)

11-19-2010, 02:57 PM   #22
markcurling
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Dark Uncle I agree with your observation - and I believe it is this observation which leads to the crazy headspace theory! The explanation is as follows...

Carbon dioxide does not dissolve very well in water. This means that the equilibrium point inside the bottle lies with 90% CO2 in the headspace, 10% CO2 in the beer. The beer stays fairly close to this equilibrium at all the time throughout carbonation/conditioning. This means that a beer which is only slightly carbonated still has considerable CO2 in the headspace, or in your instance, a beer which is perceived as flat still gives an illusional hiss!

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11-19-2010, 03:01 PM   #23
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Quote:
 Originally Posted by jourelemode i think its because the beer and the headspace has to maintain a constant state of equilibrium. Not one or the other having more co2 than the other. Because the common knowledge here is the headspace fills first then when there's no where to go it falls into solution, therefore carbing the beer. did I get that right?
well, not according to markcurling, that's "utter rubbish," funny this is the first time in years anyone's challenged it, including some of our better known beer scientists on here..

*shrug*
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11-19-2010, 03:04 PM   #24
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Quote:
 Originally Posted by JLem The yeast produce CO2 which goes into solution. The amount of CO2 that can be held in solution is a function of the temperature of the solution and the pressure - basic gas laws here. As the yeast continue to produce CO2, the solution will reach its saturation point for the current pressure, so some of the CO2 escapes into the headspace. As the CO2 increases in the headspace, because the bottle is capped, the pressure inside the bottle builds up, which increases the amount of CO2 that can go into solution - you can think of the increased headspace pressure literally forcing the CO2 back into solution until the pressure of the CO2 pushing out of solution is equal to the pressure pushing back in - the system maintains equilibrium. At some point all the sugars are used up and no more CO2 is produced. Otherwise, if you add too much sugar, too much CO2 builds up, increasing the pressure inside the bottle until the glass cannot take it any more and explodes (the force of the CO2 inside exceeds the material strength of the glass). Now, once the yeast are done converting all the sugars into CO2, there will still be CO2 in the headspace. When you then chill the beer down, more CO2 goes into solution since colder liquids can hold more gas. When you pop the top, you've released the pressure, which is the hiss you hear as CO2 escapes. With the pressure released, the beer is now out of equilibrium, so the CO2 dissolved in the beer comes out of solution once more as the system swings back into equilibrium, this time with the lowered ambient pressure. Hence, we get nice bubbles (and foam) when we pour. If you don't have a lot of CO2 dissolved in solution - either because you didn't add enough priming sugar or the yeast haven't had time to fully convert the sugar into CO2, the CO2 in solution quickly dissipates (come out of solution), and the result is flat beer (even though you heard a hiss when you popped the top)
Gee isn't that what I've been saying that I just got told was utter rubbish????
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11-19-2010, 03:04 PM   #25
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Quote:
 Originally Posted by Revvy Gee isn't that what I've been saying that I just got told was utter rubbish????
yeah, but maybe I just said it better

11-19-2010, 03:06 PM   #26
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Quote:
 Originally Posted by JLem yeah, but maybe I just said it better
Yeah that's what I'm thinking....

I'm gonna steel it from you in the "of patience and bottle condition thread." But more than likely I'll just quote it and credit you.
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11-19-2010, 03:16 PM   #27
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Quote:
 Originally Posted by JLem yeah, but maybe I just said it better
Agreed. That is the best explination I have seen thus far.
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11-19-2010, 03:22 PM   #28
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Quote:
 Originally Posted by markcurling dspace fills up with CO2 first, which then has to be forced back into the beer.
I see where the problem lies, I never said it fills the headpace FIRST. I just said it fills the headpace. Not when. Of course it is happening first in solution. But it is rising up and FILLING the headspace and then being forced back in solution.

If that's why you called it rubbish, then it's your mis reading of my explanation, not my explanation. That's flawed....
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11-19-2010, 03:26 PM   #29
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Thinking about all this raises another question in my mind. Is yeast less effective under pressure? Would that explain why it takes 3 weeks for a beer to carb?

I think the next time I bottle a batch, I will set aside 2 uncapped bottles. I will take a hydrometer reading from each bottle, return the samples to the bottles, cap one of the beers, then take another reading from both 24 hours later and see how much the gravity has changed and what the potential differences are.

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11-19-2010, 03:30 PM   #30
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Quote:
 Originally Posted by BrookdaleBrew Thinking about all this raises another question in my mind. Is yeast less effective under pressure? Would that explain why it takes 3 weeks for a beer to carb?
Yeast are inhibited by high CO2 concentrations. I do not know what direct effect pressure has on them, but I don't think any, because liquid is not compressible and yeast are not airborne.

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