Why force carbing requires low temps when natural carbing requires high temps?

[davirley]

There seems to be a disconnect between the following two pieces of information, though I believe both to be correct. What am I missing?

1) Almost all literature that I have read strongly recommends force carbonating kegs at low temperatures (below 40F).

2) On the other hand, naturally carbonating requires higher temperatures (high 60s - low 70s) so that yeast will be active and turn simple sugar into alcohol and (more importantly) CO2. Yet CO2 still dissolves in beer at these temperatures.

Why is it that natural carbonation can take place at higher temperatures, but force carbonation cannot? Maybe it is possible to force carbonate at higher temperatures given enough time and pressure (perhaps 3 weeks, as is the case for naturally carbing)?

Also, force carbonating requires higher and higher pressures as temperature increases. Does this mean natural carbonation is taking place at very high pressures? This seems unlikely given the seemingly weak structural integrity of bottles and caps, so maybe it is that millions of yeast producing CO2 at separate locations facilitates CO2 dissolution.

Any scientists out there that can explain this?

 

[insanim8er]

Liquid absorbs CO2 better at low temps. It will still absorb at warmer temps, but it requires more pressure.

Yeast will not ferment at low temps, so it needs to be warm in order to produce the CO2. It still gets absorbed regardless.

If I want 2 vol of CO2 at 65f, i'm at 21 PSI
If I lower the temp to 40, I'm at like 7 PSI

Plus, I'm pretty sure with the CO2 being produced by the yeast, it's going through the solution to help absorption while pressure carbonation is forced from the top into the solution.

 

[Beernik]

Agreed, what you are doing between force carbing and natural carbing is different.

Yeast create dissolved co2 which realeases into the headspace once it is saturated.

Force carbing puts co2 into the headspace and it has to dissolve into the beer. The solubility of co2 is higher at lower temperatures, so it the beer will carb easier.