Another noob question: if I ferment my beer @20C, and then cold-crash it for 3 days @0C then what is the temperature I should enter in these beer priming calculators? Just the 20C? Does the beer really take up a lot of CO2 when it’s cooled?
I’m asking because I looked the calculation at http://www.brewersfriend.com/beer-priming-calculator/ and with 20 liters, 2.4 volumes of CO2, the amounts for 20C and 1C are 123.1 g and 60.1 g respectively. That’s double the amount…
Yes, when the wort is cold is holds CO2. If you are cabonating at room temps, let the beer go to room temp and then add the sugar.
I’d skip the cold crash unless you have a reason. If you are priming you will have sediment in the bottle so who cares if it is the thickness of a fingernail or the thickness of a coin. It still will be there.
See, that’s what I don’t understand. Say that there’s 200 units of CO2 produced during fermentation. At the end of the fermentation at 20C, the beer looses 100 units. Now I cold-crash to 0C. Surely the beer is not going to take up again a considerable amount of C02, say 50 units?
And the cold crashing is already finished. 
You understand correctly. Most of that CO2 has offgassed through the airlock, and isn’t going to go back into the beer. The best bet is to enter the highest temperature your beer was at after active fermentation has been completed into your priming sugar calculator.
Your 200 units/100 units just isn’t real enough for this discussion. I once calculated how much CO2 was given off by fermentation and IIRC it was something like 135 gallons of CO2 in a 5 gallon ferment of 1.050 beer. (don’t quote that, it was a very long time ago)
The amount of CO2 in solution is temperature dependent. Warm it is low, cold it is higher. Play with any priming calculator just by changing the temp of the beer and you can see the relationship.
Don’t bog down on it, follow the priming calculator and prime as suggested…
I’ve never thought about priming cold - that must also add a lot of time to get to the fully carbed level, right?
Depending upon the yeast it may never carbonate properly.
So I just need to let my beer warm up to room temperature and all my problems go away magically. You guys are geniuses giant dwarfs on whose shoulders I stagger. Thanks!
Are you guys talking about carbing with sugar? Because if so, that temp in the calculator is highest temp the beer reached since it was completely finished fermentation. Right? So, if a beer finished at 68f but then warmed up to 80f, but you cooled it to 30f… ypu still use 80f in the calculator. That temp calculation is trying to account for residual CO2, and 80f would be when it off gassed the most. If the beer is done fermenting, chilling it back to 30f wont suck back in CO2.
That’s how i have always done it.
It’s also my approach with some imprecise addition of sugar for beers that have aged for a length of time.
IMO it’s extremely important to calculate from the warmest post-primary fermentation temperature for beers fermented on the warmer side like saisons. If you calculate priming weight from a calculator with a fixed temperature in the upper teens/low twenties celsius or use whatever the present temperature is but you let fermentation wrap up closer to 30C you’ll end up with one undercarbonated saison.
This is for my infamous " fast IPA" that I brewed two weeks ago and that I needed to cold crash to get it ready for a competition. I’ll let it come to room temperature by tomorrow morning and add the sugar for a 20C batch.