Bottle carbonation theory

[markcurling]

Gas only ever flows from high partial pressure to low partial pressure (i.e. towards equilibrium). Therefore CO2 will only flow into or out of the headspace in the direction of equilibrium. The CO2 is added by the yeast into the solution, which puts the CO2 in solution at a higher partial pressure than the headspace, forming a concentration gradient from the beer to the headspace.

Therefore I disagree with the wording where you say CO2 is "forced back in solution". This implies that the CO2 flows from solution, to headspace, to solution again. There can never be a time when the headspace has a higher partial pressure than the solution, so there can never be a net flow from the headspace to the beer. CO2 is added in solution, so the direction of flow can only ever be into the headspace. This is the exact opposite of force carbing, whereby you are adding CO2 to the headspace hence setting up a concentration gradient into the beer.

 

[DarkUncle]

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)

That is the process as I understood it but which it seemed, at first, markcurling was refuting. In reading through his explanation again I'm not really clear on what he disagrees with. Perhaps it's a matter of semantics here?

 

[JLem]

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.

hydrostatic pressure definitely affects the yeast - I don't know the exact biology of it, but it is often talked about when homebrewers try to mimic/clone commercial recipes. The commercial guys often have tall cylindrical fermenters, which exert more pressure on the yeast (because of that tall column of liquid pushing down), which represses ester formation (somehow) and because of this they tend to ferment at higher temps than homebrewers do.

Just because something is incompressible doesn't mean it cannot be affected by increased pressure - ever had a sinus infection?

 

[JLem]

Gas only ever flows from high partial pressure to low partial pressure (i.e. towards equilibrium). Therefore CO2 will only flow into or out of the headspace in the direction of equilibrium. The CO2 is added by the yeast into the solution, which puts the CO2 in solution at a higher partial pressure than the headspace, forming a concentration gradient from the beer to the headspace.

Therefore I disagree with the wording where you say CO2 is "forced back in solution". This implies that the CO2 flows from solution, to headspace, to solution again. There can never be a time when the headspace has a higher partial pressure than the solution, so there can never be a net flow from the headspace to the beer. CO2 is added in solution, so the direction of flow can only ever be into the headspace. This is the exact opposite of force carbing, whereby you are adding CO2 to the headspace hence setting up a concentration gradient into the beer.

OK - i see your point. It's not that the headspace forces CO2 back into solution so much as the pressure in the headspace prevents CO2 from escaping from solution. However, once you lower the temperature, we've got another story - the partial pressure of the liquid will be decreased so the CO2 will flow back from the headspace to the beer...right?

 

[markcurling]

OK - i see your point. It's not that the headspace forces CO2 back into solution so much as the pressure in the headspace prevents CO2 from escaping from solution. However, once you lower the temperature, we've got another story - the partial pressure of the liquid will be decreased so the CO2 will flow back from the headspace to the beer...right?

Agreed

Though to be 100% correct, I think when you lower the temperature, rather than decreasing the partial pressure of the liquid, you are actually shifting the equilibrium position, giving a resultant gradient back into the beer.

 

[BrookdaleBrew]

OK - i see your point. It's not that the headspace forces CO2 back into solution so much as the pressure in the headspace prevents CO2 from escaping from solution. However, once you lower the temperature, we've got another story - the partial pressure of the liquid will be decreased so the CO2 will flow back from the headspace to the beer...right?

I think this is why Revvy's explination is confusing. To me it makes it sound like CO2 created, fills the headspace and then is slowly forced back into solution over the course of 3 weeks, (which is what my entire theory was based on) when in reality, equilibrium is maintained and when the beer is chilled the equilibrium shifts.

Now I have a better understanding of what actually happens in the bottle. I'm glad I brought this up even if my theory wasn't sound.

 

[JLem]

Agreed

Though to be 100% correct, I think when you lower the temperature, rather than decreasing the partial pressure of the liquid, you are actually shifting the equilibrium position, giving a resultant gradient back into the beer.

we're just arguing semantics at this point, and I am no chemist, but, since total pressure is directly proportional to temperature and partial pressures are defined by the total pressure, doesn't lowering the temperature then also lower the partial pressures?

(Or am I erroneously using ideal gas laws to talk about aqueous solutions?)

 

[Justibone]

we're just arguing semantics at this point, and I am no chemist, but, since total pressure is directly proportional to temperature and partial pressures are defined by the total pressure, doesn't lowering the temperature then also lower the partial pressures?

(Or am I erroneously using ideal gas laws to talk about aqueous solutions?)

THIS is the can of worms.

 

[JLem]

THIS is the can of worms.

yes, but more fun (!!!!) to discuss than actually doing work!

 

[Justibone]

hydrostatic pressure definitely affects the yeast - I don't know the exact biology of it, but it is often talked about when homebrewers try to mimic/clone commercial recipes. The commercial guys often have tall cylindrical fermenters, which exert more pressure on the yeast (because of that tall column of liquid pushing down), which represses ester formation (somehow) and because of this they tend to ferment at higher temps than homebrewers do.

Yes, I remember getting involved in a "satellite" brewing discussion where this came up. It is not very relevant to bottling, unless someone is using a 6 ft tall bottle vs. 6 inches??

Just because something is incompressible doesn't mean it cannot be affected by increased pressure - ever had a sinus infection?

The differences in pressure for sinus infection are mostly relevant because of nerve stimulation. The actual differences are usually of small magnitude. Until I see a patient with the hollow space in their skull actually blowing fragments out onto the pavement... I'm gonna say sinuses are not the best example.

Deep sea submersibles... now there's an example.

 

[markcurling]

we're just arguing semantics at this point, and I am no chemist, but, since total pressure is directly proportional to temperature and partial pressures are defined by the total pressure, doesn't lowering the temperature then also lower the partial pressures?

(Or am I erroneously using ideal gas laws to talk about aqueous solutions?)

Um, possibly, I'm a bit too rusty to start delving into these realms! My instinct says that using ideal gas laws you are probably lowering the pressure of the whole closed system (both beer and headspace), however we are interested in the relative changes between the two phases inside the closed system, so there is an equilibrium shift due to the changing solubility of CO2 in water with temperature. But I don't know whether that agrees or disagrees with your point! Unfortunately I need to do something productive now, but I'll certainly check back on this thread a bit later!!

 

[JLem]

Yes, I remember getting involved in a "satellite" brewing discussion where this came up. It is not very relevant to bottling, unless someone is using a 6 ft tall bottle vs. 6 inches??



The differences in pressure for sinus infection are mostly relevant because of nerve stimulation. The actual differences are usually of small magnitude. Until I see a patient with the hollow space in their skull actually blowing fragments out onto the pavement... I'm gonna say sinuses are not the best example.

Deep sea submersibles... now there's an example.

Agreed!

 

[CplHunter]

I decided to test this theory with my latest batch and will report back with results. If anyone else has tried anything like this, I'd love to hear your experiences.

I'm curious if you've any results to report yet.

 

[BrookdaleBrew]

Nope, my theory was pretty much disproven on the 1st or 2nd page, hahaha. Didn't even bother testing it out.

 

[Bobby_M]

Hmm, how did I miss this thread? Anyway, I agree with everything Markcurling has said based on my limited knowledge of gas laws. Think of it this way, why do priming rate calculators need to account for the fermentation temperature constant? Because it determines how much CO2 is already in solution. It had nothing to do with building head pressure.

Also, it was mentioned that CO2 absorbs into colder beer faster. I think that's "rubbish" ;-) If anything, warmer beer would move dissolved co2 away from the surface faster. The only thing you can say really is that warmer beer requires a higher partial pressure for the same volume of dissolved CO2 but time? I don't think so, but I'm open to consider why it would. Anyone know?

 

[markcurling]

Hard to draw an exponential in paint, but I think you're saying it does 'a' rather than 'b'?

 

[Hockeyhunter99]

What about specific heat difference between liquid and gas. pressure difference would change slower for a liquid than a gas when the temp changes. Meaning that if a gas drops heat faster than liquid it would hold more CO2 and as markcurling has mentioned about equilibrium, force CO2 into the beer?

remember heat and temp are not the same. temp is a reading of how fast particles move divided by volume of space.

heat is how fast they move or their kinetic energy.

 

[camus]

Therefore CO2 will only flow into or out of the headspace in the direction of equilibrium. The CO2 is added by the yeast into the solution, which puts the CO2 in solution at a higher partial pressure than the headspace, forming a concentration gradient from the beer to the headspace.

There would be no gradient, the CO2 would never be in a higher pressure in the beer than in the headspace. The headspace needs to achieve adequate pressure to dissolve the C02 into the liquid. Gas, CO2, can compress, beer cannot.

 

[markcurling]

Hockeyhunter, I don't follow, are you talking about a change in carbonation rate whilst cooling?

Camus, the statement is correct, read up on partial pressures. CO2 can compress whether it's floating about in a vacuum or floating about in beer. I know wiki isn't the best source of physics knowledge, but for the sake of speed, "The partial pressure of a gas dissolved in a liquid is the partial pressure of that gas which would be generated in a gas phase in equilibrium with the liquid at the same temperature"

 

[Bobby_M]

Hard to draw an exponential in paint, but I think you're saying it does 'a' rather than 'b'?

The only difference in what I was thinking was that the pressures would be adjusted for the same volumes target. In that graph, a and b are assumed to be both for fixed pressures applied. Here's more like what I was thinking. Given equal volumes targets and appropriate pressures applied, the warmer beer would carb faster since diffusion is a function of temperature. The faster the dissolved CO2 at the surface of the beer diffuses away, the more partial pressure gradient you have at that surface. I think this is only true for externally applied CO2 as in kegging though. I don't know why I brought this up in a thread about bottle carbing. I may be so full of crap that my eyes are brown though. Help. It's not too much easier to freehand a graph in powerpoint either.

 

[markcurling]

Yes I see what you are saying, but I'm not going to agree with the outcome until I've done some more reading! Solubility and rate of dissolution are very different things - solubility depends on thermodynamics and the gas laws (as we have been discussing), rate of dissolution depends on kinetics, which uses a whole different bunch of maths (i.e. your statement about partial pressure at the boundary doesn't really apply), so to save the rest of my afternoon I'm not going to attempt to get into it! It also gets a lot more complicated - remember the CO2 dissociates as well as just dissolving, there's a lot of complicated things going on in that pint!

 

[Hockeyhunter99]

only posting to show that there are times when CO2 go back into beer. temp gradient while cooling would in fact, cause co2 to leave the headspace and enter into the beer.


p.s. while on topic. if CO2 is produced in solution, why have i seen floaters move up and down in solution making and release gasous CO2 bubbles? is there a nucleation site for the production to take place?

General term of "floaters" can be taken due to unknown specific content.

 

[camus]

Hockeyhunter, I don't follow, are you talking about a change in carbonation rate whilst cooling?

Camus, the statement is correct, read up on partial pressures. CO2 can compress whether it's floating about in a vacuum or floating about in beer. I know wiki isn't the best source of physics knowledge, but for the sake of speed, "The partial pressure of a gas dissolved in a liquid is the partial pressure of that gas which would be generated in a gas phase in equilibrium with the liquid at the same temperature"

Your assuming everything is perfectly stable and immediate. The rate at which C02 dissolves is dependent on the pressure of the headspace, the amount of common surface area and temperature of the beer. Regardless the CO2 will continuously flow in and out of the headspace (eventually with perfect conditions all activity would cease). The yeast would die far before pressures where great enough for the C02 to instantaneously dissolve, even if that would occur given there is a headspace.

Given that, the yeast are producing CO2, CO2 that is not just floating around in the beer, it is floating up rapidly, maybe some dissolves, but the majority will make it to the headspace, increasing pressure, and then slowly dissolve into a nice carbonated beer.

 

[markcurling]

Given that, the yeast are producing CO2, CO2 that is not just floating around in the beer, it is floating up rapidly, maybe some dissolves, but the majority will make it to the headspace, increasing pressure, and then slowly dissolve into a nice carbonated beer.

Going in circles now, yeast produce CO2 in solution (i.e. 100% dissolved, not floating about in bubbles) - read back through the first couple of pages of the thread

 

[Justibone]

Yes, CO2 is produced in solution, but it can potentially bubble out.

It's unlikely to bubble out due to nucleation so long as the pressure is maintained.

If bubbles are popping off of "floaters" it's more likely that the floater was near the surface and grabbed a bubble that way, rather than nucleating it.

 

[camus]

Going in circles now, yeast produce CO2 in solution (i.e. 100% dissolved, not floating about in bubbles) - read back through the first couple of pages of the thread

Yeah, I guess we are and I apologize for belaboring the point. I interpreted dissolved as being aqueous, which has another set reactions occurring beyond yeast producing CO2.

 

[Righlander]

i had a similar query a few years ago, but slightly different: i was just curious what would happen if i put one bottle of beer in the fridge right after bottling, here's what happened...
it was ed wort's apfelwein, i primed, bottled then stored all but one as normal for room temp conditioning. so anyway in a matter of 2 months i drank all the apfelwein except for the one in the back of the fridge, i cracked it open and it was perfectly carbed and tasted very clean, maybe even more clean than the others. i might try that again when i bottle my IPA in a couple days.

 

[Justibone]

If you do it again, use at least three bottles in the fridge, and three more at room temperature. Test them at the same age: i.e., if you test at 2 months, test one refrigerated and one room temp (RT).

When the time comes to taste them, have someone else pour them so you don't know which is which. Pour three small sips; two from the RT bottle and one from the cold bottle. Taste all three and see if you can taste which was cold-carbed. Do it again, but this time with different bottles and two tastes of cold-carbed and one taste of RT, see if you can tell which was which.

Three samples (bottles in each condition - room temp and refrigerated) should give you more statistical "power"... your results are more likely to be accurate.

http://en.wikipedia.org/wiki/Statistical_power

Tasting three samples, two taken from one bottle and one taken from the opposite condition bottle, is called a "triangle test" and is considered more accurate for taste-testing purposes.

http://www.shvoong.com/exact-sciences/5671-food-science-triangle-test/

That would be a very interesting experiment.

 

[Righlander]

If you do it again, use at least three bottles in the fridge, and three more at room temperature. Test them at the same age: i.e., if you test at 2 months, test one refrigerated and one room temp (RT).

When the time comes to taste them, have someone else pour them so you don't know which is which. Pour three small sips; two from the RT bottle and one from the cold bottle. Taste all three and see if you can taste which was cold-carbed. Do it again, but this time with different bottles and two tastes of cold-carbed and one taste of RT, see if you can tell which was which.

Three samples (bottles in each condition - room temp and refrigerated) should give you more statistical "power"... your results are more likely to be accurate.

http://en.wikipedia.org/wiki/Statistical_power

Tasting three samples, two taken from one bottle and one taken from the opposite condition bottle, is called a "triangle test" and is considered more accurate for taste-testing purposes.

http://www.shvoong.com/exact-sciences/5671-food-science-triangle-test/

That would be a very interesting experiment.

you know what, i'm bottling my IPA tomorrow afternoon. i like the sound of this test. i'm going to try it. i'll update the results when the time comes. thanks for the idea!