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When using CO2 calculators or the nomograph on Palmer's site we see that depending on the temperature of your beer, you use a different amount of priming sugar in order to get the same effective carbonation. Why would temperature effect the amount of CO2?

My (incorrect) logic goes like this: You put "X" number of yeast cells into a bottle with "Y" amount of food. When the yeast are done, you have "Z" CO2. So if you do two bottles, both with X and Y counts, and one bottle is warmer, then all of the food might get consumed sooner (presuming both temperatures are keeping the yeast happy), and you get Z CO2. But the cooler bottle, once all the food is gone, should also have Z CO2, not Z plus something.

So what is going on that changes the food to CO2 ratio when temperature changes?

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It's not the temperature of bottle conditioning, it's the temperature of the fermented beer that you're adding priming sugar to. –  baka Jun 10 '12 at 16:33

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What you're not accounting for is the CO2 produced during fermentation. The colder the beer ferments, the more CO2 will be in solution in it. That kinda gives you a "head start" on carbonation. If you don't account for the CO2 retained, your beer can be either over or under carbonated.

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So when bottling lagers, would you say its a good rule of thumb to bring them up to room temp for a day or two before bottling, to let that extra C02 in suspension bubble out? That way, say, 4oz of Dextrose will give you the same carbonation in a lager as in an ale? –  Graham Jun 11 '12 at 12:55
    
Very smart Denny! Excellent. Not sure why I didn't think of that, but makes perfect sense. –  Dale Jun 11 '12 at 14:27
    
Graham, that's what I do. It's not 100% effective, but I find it easier than trying to figure out how much dissolved CO2 is in the beer. Yeah, I know, I'm lazy.... –  Denny Conn Jun 11 '12 at 14:49
    
co2 is solvent in solutions. the cooler the temperature of the liquid the more co2 can be absorbed. another reason why you want to chill your brew before opening. –  Jason Meckley Jun 12 '12 at 12:04

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