Calculating Dissolved CO2 Post-lagering

[troglodytes]

Hey All,

I know this discussion has come up in the past, but I feel I don't have a clear cut answer as to how much CO2 is naturally in my post-lagered brew prior to bottling. I am going to use the krausening method to bottle carb and condition, but I'm not sure what temp to use to calc the current dissolved CO2 level.

I fermented Wyeast 1007 for a week at 63F, ramped it to 68F for 2 day D-rest, cooled back to 66F for about a day before lagering for 2 weeks in the mid-30s. So how much CO2 is in the beer? Do I use 68F, 66F, or 36F?

I've heard to use the highest temp the beer has reached after reaching FG? If that is the case then I would use 66F. However, wouldn't the headspace still be full of CO2 when lagering, and wouldn't some of that CO2 be retained at the 36F rate?

It doesn't seem like that big of a deal, but the total difference in vols is .5 according to the Brewer's Friends calculator. this is huge when you compare a beer carbed to 2.0 vols vs. 2.5.

 

[zachattack]

I've heard to use the highest temp the beer has reached after reaching FG? If that is the case then I would use 66F. However, wouldn't the headspace still be full of CO2 when lagering, and wouldn't some of that CO2 be retained at the 36F rate?

Yup, use 66. Some of the residual headspace CO2 will be absorbed when you go lower, but since you are no longer generating CO2 it should be negligible. Unless you have a huge headspace and a tiny beer volume

 

[progmac]

Maybe it helps to think about what is going on. When beer ferments, the yeast creates a bunch of CO2. Cold liquid holds more CO2 than warm liquid. So when you ferment, most of the Co2 is blown off, but some stays in the liquid. The amount depends on the temperature of the liquid. If you ferment something warm then cool that liquid down after Co2 is done being produced, there is no magic that brings CO2 back into solution--ergo the amount of Co2 is, in general, based on whatever the temperature of the liquid was when Co2 stopped being created or the warmest temperature where the liquid has rested for any significant amount of time, provided that gas could vent.

 

[Yooper]

Since you did the diacetyl rest at 68, much of the c02 produced during fermentation would be released.

I hate priming calculators but if you must use one, use 68 degrees for the temperature.

 

[troglodytes]

Awesome, thanks for the feedback. The calculator is a bit misleading when it asks for "Bottling Temp" to calc CO2 levels.

Looks like I'm going to need to make a large krausen beer to carb, which is good to know in advance of bottling. Thanks again.

 

[zachattack]

Yup, use 66. Some of the residual headspace CO2 will be absorbed when you go lower, but since you are no longer generating CO2 it should be negligible. Unless you have a huge headspace and a tiny beer volume

I meant 68, not 66. Like you said, highest post-fermentation temperature.