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priming problem - how to judge residual c02 correctly

jonnym_ch

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hi all,
i have an ipa that i transferred to secondary and is cold-crashing at the moment.
after transferring to secondary i put straight into the fridge and loosely capped the carboy with foil so, in theory, the headspace above the beer would have been pretty much free of c02.
the temperature at fermentation was around 21?C (70?F) and fermentation had finished 2 weeks prior to transferring the fridge at around 4?C (39?F).
my question is, how do i calculate the amount of priming sugar needed based on residual c02 ? should i assume that the residual c02 at time of transfer (while the beer was 21?C / 70?F) is the one to use as it would not have increased during the cold crashing phase due to the top being not completely sealed and no additional c02 dropping back into the beer ?
i know that there seems to be lots of conflicting opinions on this out there so any clarification would be much appreciated !
cheers,
jon
p.s. hope the question is clear ... don't hesitate to ask if you need any additional deets !
 
Without getting too complicated, the maximum amount of CO2 in your beer, after you racked, would've been 1 volume.

CO2 would not "drop back into the beer." The gas remains at equilibrium. If anything, the carboy being open to air would allow oxidation to occur. An airlock prevents gas exchange like that.

When you prime, the doses calculated assume some CO2 in the beer.  Just using the dose recommended for carbonation will work out. No extra math required.
 
hi brewfun,
and thanks for your reply !
it's really interesting (and slightly confusing) that almost every article i come across online, including the priming calculator i use, says that c02 will drop back into the beer during cold crashing ???
anyhow, i found this article (http://beerandwinejournal.com/residual-co2/) which confirms what you said and explains it really well ... i think ;).  if i understood correctly, c02 cannot increase after fermentation but it can be reduced if the temp increases (as in a diacetyl rest). as i didn't do that i'll just take the temp when fermentation stopped and use that.
cheers,
jon
 
jonnym_ch said:
it's really interesting (and slightly confusing) that almost every article i come across online, including the priming calculator i use, says that c02 will drop back into the beer during cold crashing ???

I think the point the articles are making is that colder beer will retain more CO2, *if* it's generated by fermentation or external force. In a pressurized environment, like a bottle or keg, chilling the beer will make the gas in the headspace equalize with the beer. In that way, yes, CO2 would be absorbed. However, that doesn't apply to your example of racking and storing your beer.

Using the warmest temperature the beer achieved for your priming calculator is correct.
 
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