Originally Posted by Bobby_M
The only way it would be devoid of CO2 is if you pull a vacuum on the carboy. Residual co2 calcs are based on the partial pressure of ambient air.
This isnt entirely true, Ive brewed many many sours and I think other people will tell you this as well, the problem a lot of times on older (1yr+) sours when priming is to actually carbonate to adequate levels, I understand the CO2 levels are dependent on the partial pressure of the gas in the atmosphere, that henry's law at its simplest, but dissolved co2 is also a function of pH, lower pH = less dissolved CO2, however due to the kpa of co2 species it should be constant below 5.5 and all should be in the form of H2CO3 (forgive me for rambling thinking while i type) so theoretically what you said should be true, however you have to remember that henry's law constants arent exactly constants and things like density pH etc can swing them one way or the other
To be honest I hadnt given much thought to the science basis for it, but maybe I should now....I always had to really think about aqueous CO2 concentrations because of how the gas acts like a weak acid depending on pH
A couple interesting things I found while looking for an answerhttp://www.iul-instruments.de/pdf/vitalsensors_2.pdfhttp://www.anton-paar.com/001/en/Web/Document/download/702?clng=en