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So beer temperature affects residual co2 in beer for priming, the lower the temp the more residual. I've got a Ryepa that I plan on carbing to 2.4 vols of CO2. Its been in a 55 degree closet for 4-5 days, should I use temperature compensation for that current temp of 55 or the 63 degrees it was at before crashing?

For a 5 gallon batch the higher temp actually only adds around .3 ounces of cane sugar....guessing that won't make much of a difference.

I guess a side note, which calculator do you guys find to be more accurate....HBD or NB's calc? Usually there's not much more than a fraction of an ounce difference with HDB being higher.

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Okay guys, I asked the same question on NB's forums. The below reply is from gregscsu " You will want to use the highest temperature the beer reached post fermentation. If the beer never went above 63F at any point use that number. Or if you raised the temp to 68F at the end of primary to ensure attenuation then you would use that number." –  dsidab81 Mar 15 '12 at 14:43
    
If you are talking about residual CO2 dissolved in the beer, then that answer is wrong. The residual dissolved CO2 will equilibrate based upon the temperature the beer. So the correct answer is the current temperature of the beer, not the highest it was during your fermentation. –  Chris Plaisier Mar 15 '12 at 17:09
    
"if your beer warms up after fermentation, it will lose CO2. This will not happen instantaneously, though. However, lowering your beer’s temperature will not increase the level of CO2, unless a source of CO2 is present. (Continuing fermentation or CO2 from an outside source — like CO2 cylinder — are the two most likely possibilities.) If you want to accurately estimate your residual amount of carbon dioxide, hold your fermentation temperature constant and add the priming sugar to the beer at this same temperature. You may then warm the beer up for bottle conditioning,if needed" –  dsidab81 Mar 15 '12 at 21:28
    
That above quote was from the byo article below. Although he mentions a stable fermentation temp, but it also makes sense that more CO2 is not created by cooling the beer. Lately i've primed my beer to my last secondary temp and have had mixed carbonation issues. I will attempt in the two batches this weekend to carb to my average fermentation temp. I'll report my rather un-scientific findings :0 –  dsidab81 Mar 15 '12 at 21:29
    
Okay well I think that the BYO article is incorrect about "lowering a beers temperature will not increase the level of CO2". Even in 1 atmosphere of CO2 changing the temperature changes how much CO2 is dissolvd in water. And we are just talking air here, no needed excess CO2 produced by yeast. Take a look at this: docs.engineeringtoolbox.com/documents/1148/… –  Chris Plaisier Mar 16 '12 at 14:29

3 Answers 3

up vote 3 down vote accepted

The difference in volumes of dissolved CO2 at 55 v. 63 is only 0.15 volumes; according to Section B.
That difference will be hardly noticable on the tongue or in the glass, and it certainly won't cause a bottle bomb situation. If anything the beer will be slightly overcarbed, which is better than under carbing.

I used to bottle for years before anyone started worrying about dissolved CO2 post ferment. The differences are so small its a minor thing to concern yourself with, IMO. I can't say all my lagers were overcarbed and my ales weren't.

As homebrewers we (myself included) can get trapped in the absolutes of what beer math and physics tell us. I present this difference to remind us to always think about the practical aspects of what we are doing. That's the balance between the art and the science of brewing. Professionally I am a hard bench scientist, but even I recognize and remind my coworkers of the need to keep it in perspective of the goal.

So my answer to the question is to go with 63F, realizing that for any point of reabsorption below that due to headspace CO2 is going to be trivial.

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I also am a biologist, although I don't hit the bench often enough. :-) I agree with your assertion that the effect size will be small. However, as you surely know reducing all types of variation improves your ability to reproduce results, in this case properly carbonated beer. –  Chris Plaisier Mar 18 '12 at 16:07
    
great answer. practical experience always better than just reading a textbook. –  mdma Mar 18 '12 at 18:48

I would use the highest temp achieved during or after fermentation with a caveat that some of the C02 expelled at the highest temp will get sucked back into the beer if/when the temp drops, just like a bottled beer sucking it the carbonation in the headspace. The size difference between a bottle's headspace and its liquid content is proportional to the empty/filled space of a 5gal secondary carboy with a 5gal batch in it.

HOWEVER, if at any time after the high point of fermentation was reached, but before the lower temps occurred, if you opened the fermentor sufficiently to allow for the escape of that headspace C02, then that C02 obviously won't be present to be re-absorbed by the beer as the temp of the carboy is lowered, thus you would need to use more priming sugar than if that headspace C02 was re-absorbed by a cold crash, for example.

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Your analogy is interesting. But I have to say your second statement is slightly flawed. Gases can fairly easily diffuse through an airlock (mocon.com/pdfoptical/…). Even so, the CO2 levels don't need to be elevated in order to increase the residual CO2 in the beer, the temperature just needs to change in normal air and you would get a different residual CO2 level in the beer. –  Chris Plaisier Mar 16 '12 at 14:46
    
Temperature change alone isn't enough for C02 re-absorption though. You also need available C02 in the air to be pulled back in, right? So if all the C02 theoretically leaves the headspace via the airlock, then there would be no C02 to be re-absorbed and cause over-carbonation in the bottling. –  Graham Mar 16 '12 at 14:55
    

Looking around it seems that the answer is go with the 55 degrees. Because CO2 was dissolving into your beer even while it was cold crashing. So basically if you are going to prime at 55 degrees, use 55. But if you are going to let it warm up and then prime, then use that temperature (say 63 degrees you mentioned). Note that at 55 degrees it may take quite a while for the yeast to produce the CO2 to carbonate the beer. Bringing the bottles or keg up to room temperature for a while will help speed that process along. Here is a BYO article on priming: http://www.byo.com/stories/article/indices/21-carbonation/1276-priming-with-sugar

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