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najel 01-26-2013 01:52 PM

Compensate for already dissolved CO2
Hey guys and gals!
Just a quick question. I am going to bottle a Hefeweizen this weekend. When I pulled gravity samples, I noticed that there were lots of little bubbles coming up in the sample tube. Seems to me there is a lot of residual CO2 from fermentation still dissolved. Now I use Beersmith to calculate the amount of priming sugar needed. But I fear that, since I am going to carb this pretty high, and if there is already so much CO2 in the beer, I might overcarb.
Is there a good way to compensate for this? Or just don't sweat it?

mrduna01 01-26-2013 01:54 PM

How long has it been in primary? Might be it isn't quite finished yet.

Erroneous 01-26-2013 01:58 PM

I wouldn't sweat it, but if you want you could probably let it sit at room temp for a couple days.

Here's what BYO says about it:
CO2 in Flat Beer. Depending upon the temperature of your beer and how much it has been shaken around, you’ll have varying amounts of CO2 in your “flat” beer. The more you start with, the less you need to add with the bottle fermentation. Bottlers often overlook the fact that there is quite a bit of CO2 in solution in so-called “flat” beer after fermentation. If you fermented at 60 F, you already have one volume of CO2 in your beer. If you lagered near 32 F, you could have as much as 1.7 volumes of CO2 — that’s two-thirds of the final amount of CO2 you’re after! This dissolved CO2 is one reason airlocks might continue to bubble after the fermentation is done. The equilibrium table can be useful when bottle conditioning to let you know how much CO2 is in your beer before you add the priming sugar.

najel 01-26-2013 02:34 PM

Thanks for the replies!

I am pretty sure it is finished, been at 1.012 for a few days, and it's actually a little bit below what I had planned. I like to bottle my Hefeweizen after 10-14 days in primary, I think it tastes best 3 to 4 weeks after brewday. Not a beer that needs a lot of aging.
Anyway, the BYO quote is interesting. Thanks for that. I have it sitting at room temp, but it sits in a tiled floor, no basement underneath, so the beer temp is around 60. So maybe I will assume that there is already quite a bit of CO2 in there.
I think I will adjust my priming sugar amount down a bit to be sure I don't get bottle bombs. I was going to shoot for 2.7 vols in beersmith, so maybe I will just go with 2.4 or something like that and see where it gets me. I think that the beer will lose some of the CO2 during transfer into the bottling bucket, too.

eric19312 01-26-2013 04:15 PM

I use this priming sugar calculator from the northernbrewer website.


For beer temp I use the temp in the bottling bucket assuming by the time I start filling bottles that will be a few degrees warmer than fermentation temp. I mostly brew ales and don't mess with cold crashing. I think if I did cold crash the beer before bottling I wold use the fermentation temp instead of the bottling bucket temp since probably very little additional CO2 would be expected to be generated and dissolved during cold crash.

Lagers may be a different story. Seems possible over a 6 to 8 week lager you might get some additional CO2 dissolved. Or you might not and no good way to know. if you bottle based on primary fermentation temp or ecen worse diactyl rest temp and you did disolve more CO2 during bottling, then you
Probably over carb... so for lagers I take the fermenter out of the lagering fridge day before bottling and let temp rise. As the temp rises the dissolved CO2 comes out of solution and you can use the temp in the bottling bucket.

day_trippr 01-26-2013 04:18 PM


Originally Posted by najel (Post 4828733)
[...]Seems to me there is a lot of residual CO2 from fermentation still dissolved. Now I use Beersmith to calculate the amount of priming sugar needed.[...]Is there a good way to compensate for this? Or just don't sweat it?

The Beersmith2 Carbonation Tool already provides the compensation for this phenomenon - as long as you fill in the entry for "Bottling or Keg Storage Temperature" field.

Exposed to atmospheric pressure, the amount of carbonation that the fermented beer can hold is temperature dependent, so as long as Brad is using that field correctly, the amount of priming sugar will vary correctly to achieve the desired carbonation level...


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