Carbonation tool temperature confusion? Are we doing it wrong?

[rehabs_for_quitters]

Is Beer Smith possibly assuming your bottling temp is the same as ferment and condtioning temp that it works out for the style though and working it out on that?

Not trying to pick holes in your ideas Doc but it would be interesting to know if that was the case

 

[verysupple]

Is it really correct to say that a liquid not under pressure will not retain some dissolved CO2? Based on your Dad's mate's theory, there is no residual CO2 in our beer before we carbonate it, and yet we factor this into our priming sugar calculations.
Just because it tastes/feels flat doesn't mean no CO2 is dissolved into the beer, just not enough to make it effervescent. If colder beer retains more CO2, it makes sense to me to use the highest temperature post fermentation, because it's at this point that the beer relinquishes the most dissolved CO2.

The text in red brings up a very important point. What is "not under pressure"?

It depends what you mean by not under pressure. I assume you mean under ambient air pressure...which is not zero (average of 101.325 kPa at sea level). So, if a liquid really was at zero pressure it would not retain any CO2. Under ambient pressure it certainly will retain some CO2 and the amount will depend on the ambient pressure (which as we know fluctuates, but not enough to really matter for us), the CO2 concentration of the environment (yeah, we're getting into partial pressures again...) and the maximum temperature at which the beer was held for a reasonably long amount of time. The time matters because the CO2 doesn't just dissipate immediately when the temp. changes, it takes a while to reach equilibrium.

When the beer in the FV is chilled it will not reabsorb CO2 if it is kept at ambient pressure because the CO2 concentration of the air is lower than that of the beer (the head space will not be only CO2 after fermentation). When the carbonated, packaged beer is chilled it may reabsorb a small amount more CO2 than the same packaged beer at room temp, but the difference will be small because the head space is a small fraction of the total volume and so the effect of partial pressures is smaller than when the beer is interacting with the atmosphere.

So yes, the text in blue, and the OPs original approach, is correct. The dad's mate was also correct, he just forgot that ambient pressure is not zero pressure. I hope this sorts it out. Any questions? I might have skipped something.