Head space and effect on carbonation

[rwh]

I had an interesting experience the other day. I was trying a new brew that I had put down a couple of weeks earlier.

Now, often when I bottle a brew, the very last stubbie isn't quite full. I use this half a stubby as a taste tester as if it's not ready yet I've only wasted half a stubbie rather than a full one. On this occasion, it was rather less than half-full, say about a third of a stubbie.

So I opened it, got a massive SHHHHHHHH sound, and the beer was very fizzy, and had a huge gassy head. So my mind immediately raced back to when I'd bottled... how much dex did I use? How long was it in the fermenter? How oh how could I have produced an overcarbed beer!? Visions of bottles blowing up and severing the arteries in my arms and slicing into my unprotected eyeballs commenced, making me afraid to go near my beer stash.

I managed to overcome my fears, and very gingerly put a longneck of the stuff (a Mountaingoat Hightail clone, by the way) into the fridge, breathing a sigh of relief once it got down to the lower temps. Once it was cold, I opened the longneck... and it was perfectly carbonated!

I just realised what effect headspace has on a beer: I reckon the most important factor is the oxygen in that air, as aerobic respiration of yeast produces three times as much CO2 as anaerobic respiration.

[alangman]

Interesting little find. I've wondered about this myself. There is one thing I'll point out though, if it did undergo aerabic fermentation, you sucessfully converted sugar into water Not a problem in a test bottle though

BTW. I've been having some priming issues. I bulk primmed 180 g LDM to 22 L pale ale and this resulted in a flat beer (after nearly 1 month in bottle). Next batch, I added 230 g of wheat malt to 22 L of amber ale. The beer has some fizz and a nice intial head but the head dies and the beer goes flat fast (after 2 weeks in bottle).

Any thoughts?

Cheers,

Adam L

[ajoleary]

This might be an obvious question, but you didn't use the same full stubby amount of Dextrose for your 1/3 stubby did you

Otherwise that will be why!

[rwh]

Bulk primed, so no.

[chris.]

I had an interesting experience the other day. I was trying a new brew that I had put down a couple of weeks earlier.

Now, often when I bottle a brew, the very last stubbie isn't quite full. I use this half a stubby as a taste tester as if it's not ready yet I've only wasted half a stubbie rather than a full one. On this occasion, it was rather less than half-full, say about a third of a stubbie.

So I opened it, got a massive SHHHHHHHH sound, and the beer was very fizzy, and had a huge gassy head. So my mind immediately raced back to when I'd bottled... how much dex did I use? How long was it in the fermenter? How oh how could I have produced an overcarbed beer!? Visions of bottles blowing up and severing the arteries in my arms and slicing into my unprotected eyeballs commenced, making me afraid to go near my beer stash.

I managed to overcome my fears, and very gingerly put a longneck of the stuff (a Mountaingoat Hightail clone, by the way) into the fridge, breathing a sigh of relief once it got down to the lower temps. Once it was cold, I opened the longneck... and it was perfectly carbonated!

I just realised what effect headspace has on a beer: I reckon the most important factor is the oxygen in that air, as aerobic respiration of yeast produces three times as much CO2 as anaerobic respiration.

As I understand it, regardless of the amount of headspace, the gas pressure in the headspace & the amount dissolved in the beer are equal. Hence a bigger headspace will create more of an imbalance upon opening, & therefore a bigger SHHHHH & more head, than a smaller headspace will.
If that makes any sense

[111222333]

This isn't quite true, because whilst the aerobic produces more CO2, there is a far greater volume for the CO2 to fill, and hence will not dissolve in the beer, as this will only occur when the partial pressure of CO2 above surface reaches critical.

[chris.]

there is a far greater volume for the CO2 to fill, and hence will not dissolve in the beer, as this will only occur when the partial pressure of CO2 above surface reaches critical.

I think that this is initially the case but given time the pressure eventually equalizes?

[pacman]

Purchased a mixed 6 pack of Grand Ridge a few months ago. Head space in each stubbie varied, from the traditional 5cm or so, to as little as 1cm.

All brews are bottle conditioned, but the varying head spaces did not have any noticeable affect on carbonation. Guess it could be a different story if there was no head space whatsoever. Who knows? Someone probably does.

Interesting though, isn't it?

[111222333]

ay lad tiss interesting. was thinking about it more, and if we include the states in the famous equation:

C6H12O6(s) (glucose (solid)) + 6O2(g) + 6H2O(l) --> 6CO2(g) + 12H2O(l)

we see that both sides of the equation contain the same amounts of gaseous molecules. so each time six CO2 molecules that causes pressure is released from aerobic respiration, a six O2 molecules (that also cause pressure) are used, so overall, no net increase in pressure. it doesn't really mater HOW large a gaseous molecule is, just how many (the collision theory). i know im on the road to nowhere now. bringing in uni stuff to hb ... dark dark path i do fore see ...

[alangman]

Hi All,

I'm trying to do some calcs. What is the pressure inside a "normal stubby" at 20 degrees C?


Cheers,

Adam L

[blandy]

from http://www.truetex.com/carbonation.htm

sorry about the imperial units. I'll get to work on this after I finish my chem revision.

Physical Properties of CO2 Relevant to Carbonation

Density (gas) 0.1234 lb/cu-ft at 32 deg F, 1 atm
(1.98 grams/liter)
0.1146 lb/cu-ft at 77 deg F, 1 atm

Solubility in water 1.79 (vol/vol) at 32 deg F, 1 atm
Henry's law constant
(Inverted to express molar solubility) 0.117 mol/liter-atm at 32 deg F
= 1.72 volumes/atm
=? 0.034 mol/kg-bar (NIST)

[blandy]

On second thoughts, wouldn't keg pressure be the same as bottle pressure? What's a good keg pressure? this would be guage pressure, so add 1atm to it and you'd have the absolute pressure inside a keg, which I'd assume to be similar to the absolute pressure inside a beer bottle, since they'd have the same level of carbonation.

[alangman]

Hi all,

I'm a chemical engineer, so I can clear up this debate a little. The relative amount of CO2 in the headspace is not equal to the relative amount of CO2 in the beer.... but they are related. There is an equilibrium between the gas phase and liquid phase based on the solubility of CO2 in the liquid. Under pressure, the beer supersaturates with CO2 and hence bubbles when the pressure is releases and continues to bubble as the temp increases. This is because gases become less soluble in liquids as the temperature rises (this is why O2 is removed from the wort during the boil).

Ok, I've spent several hours (yes hours!) calculating what should happen when a bottle is "full" vs "1/3 full". I'm a chemical engineer and this problem was still a bastard! Any way, I'm not going to explain how this was done, it'd take too long. But here are the results along with the assumptions.

Assumptions:

• 3.5 g of priming sugar is used per 345 ml of beer.
  That the wort is at 20 degrees C, is saturated with CO2 and N2 and has no O2 in it.
  That N2 has the same solubility as CO2.
  The stubby has a volume of 375 ml
  And finally, than any O2 in the head space is totally consumed by aerobic fermentation.

Results:
the first column is for a "normal stubby". The right column is for the "1/3 full" stubby.

• Volume of beer----------------345 ml ----------- 125 ml
  Volume of headspace -------30 ml ------------- 250 ml
  Pressure -----------------------2.74 ata -------- 1.36 ata
  Co2 Level ---------------------4.62 g per L ----- 2.30 g per L
  
  Total CO2 ----------------------1.74 g Co2 ----- 0.91 g Co2

So, from this we can see that the total pressure and the amount of CO2 is lower if the stubby is only 1/3 full when it is sealed......

.....so why does it make more noise? I suspect this has something to do with acoustics. I'm guessing that the amount of noise and its duration has something to do with both the absolute pressure difference and the volume of the container. But this is a bit of a guess. Acoustics are not my field.

Last, this also indicates that the beer in the 1/3 full stubby should be quite flat. At 2.3 g/L, it has the carbonation of a british ale at best. Compared to 4.6 g/l for the "normal stubby" which is a ... well... normal figure for most beers.

So, next time this happens to someone, please taste the beer and see if you think it's flat. Then, let us know.

Hope that this helps.

Cheers,

Adam L

[chris.]

.....so why does it make more noise? I suspect this has something to do with acoustics. I'm guessing that the amount of noise and its duration has something to do with both the absolute pressure difference and the volume of the container. But this is a bit of a guess. Acoustics are not my field.

Last, this also indicates that the beer in the 1/3 full stubby should be quite flat. At 2.3 g/L, it has the carbonation of a british ale at best. Compared to 4.6 g/l for the "normal stubby" which is a ... well... normal figure for most beers.

So, next time this happens to someone, please taste the beer and see if you think it's flat. Then, let us know.

Hope that this helps.

Cheers,

Adam L

Cheers for clearing that up Adam. Damn the confusion between the terms Equal & Equilibrium

This is something that had me pondering for a few hours last night too. & I'm not quite sure if I totally understand the physics behind it... Damn Henry & his silly law
I too found myself agreeing with your comments about the resulting beer more than likely being flatter than usual after all the commotion of cracking the seal has died down.
My drunken theory is that due to the equilibium in the bottle, & the larger amount of headspace (which would have the effect of releasing more CO2 in a smaller amount of time than a smaller headspace), the CO2 in solution is somehow forced/pulled out alot quicker than usual in an effort to retain some sort of equilibrium. But of course this is all just drunken rambling.. & I've probably just repeated what you've already stated but a lot less coherantlyly ...blah

[alangman]

[Ahutchy]

Maybe with all that O2 available some wild yeast or infection of some kind went berserk or as it was the last bottle filled it had heaps of yeast in it. This combined with the extra O2???

Andrew.

[rwh]

Y'know, you might just be right... it did taste a little funny. In fact I thought to myself that it was going to be my first nightmare brew.