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12-17-2009, 04:36 PM   #1
rocketman768

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Feb 2008
Evanston, IL
Posts: 1,083
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Does anyone have an approximation to the amount of dissolved CO2 in beer as a function of CO2 partial pressure, temperature, and pH? I don't want an online calculator, but the actual formula for the approximation.

12-17-2009, 04:39 PM   #2
TipsyDragon
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Mar 2009
California
Posts: 2,607
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check this site out

scroll down a bit its near the middle.

12-17-2009, 04:58 PM   #3
rocketman768

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Feb 2008
Evanston, IL
Posts: 1,083
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Quote:
 Originally Posted by TipsyDragon check this site out scroll down a bit its near the middle.
Although it doesn't explicitly state it, it looks like they use a quadratic approximation which is:

3.0378 - .050062 * T + .00026555 * T^2

...where T is degrees F. This is ok I guess. But, usually quadratic approximations are only best-fit lines and not the actual approximation from physical laws, and I expect an exponential-like formula for this.

12-17-2009, 06:31 PM   #4
TipsyDragon
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Mar 2009
California
Posts: 2,607
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from the sound of your question it sounded more like you where asking about force carbing a keg. the equation for that is:

-16.6999 - 0.0101059 * T+0.00116512 * T ^2+0.173354 * T * Vol +4.24267 * Vol - 0.0684226 * Vol ^2

where T is degrees F and Vol is volumes of CO2 you want. but i do agree that that is just a best fit equation.

01-03-2010, 06:44 PM   #5
john from dc
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Jan 2008
Posts: 394
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well, this isn't a complete answer to your question but henry's law is a start. for a given solute (co2) and liquid, the ratio between pressure and co2 concentration is constant at a given temperature.

as for calculating that constant, there seem to be a few different methods but all that i've found are essentially approximations. i haven't seen any that are derived explicitly from first principles. but this is pretty common in chemistry and physics.

i remember as an undergrad being surprised to learn that much of what we "know" boils down to: observe a phenomenon, write an equation that describes it. there are a lot of "whys" that just aren't explained. at first it was pretty disillusioning, but i now see those unresolved questions as job security

11-09-2013, 09:12 PM   #6
DrKarma

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Feb 2009
Sweden
Posts: 163
Liked 3 Times on 3 Posts

Know this is an ancient post but as I just coded a little device that does calculations for dissolved CO2 here are the formulas that I use (Based on Zahm Nagels chart)

Temp - Formula
30 F 0,1097936017X+1,7052941176
31 F 0,1074406605x+1,6720915033
32 F 0,104747162x+1,640575163
33 F 0,1033436533x+1,6015686275
34 F 0,1015583075x+1,5679738562
35 F 0,0993498452x+1,5345098039
36 F 0,0970588235x+1,5018300654
37 F 0,0960887513x+1,4599346405
38 F 0,0945201238x+1,4303921569
39 F 0,0932817337x+1,3988235294
40 F 0,0912693498x+1,3762745098
41 F 0,0905572755x+1,3391503268
42 F 0,0898555212x+1,3047058824
43 F 0,0882352941x+1,2817647059
44 F 0,0864602683x+1,2608496732
45 F 0,0850773994x+1,2362091503
46 F 0,0845820433x+1,1998039216
47 F 0,08308856553x+1,1756862745
48 F 0,0819195046x+1,1506535948
49 F 0,080505676x+1,1313071895
50 F 0,0798348813x+1,1015686275

x is the pressure in PSI
__________________
My system build

11-10-2013, 02:02 PM   #7
ajdelange
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Aug 2010
McLean/Ogden, Virginia/Quebec
Posts: 9,418
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This is indeed an old thread. Nonetheless, taking the ASBC chart (Zahm - Nagle chart is taken from the ASBC MOA) as gospel the most robust fit is probably

V = (P + 14.695)*(0.0181 + 0.090115*exp( (32-T)/43.11) ) - 0.00334

Where V is in vol/vol, P is in psig and T in Fahrenheit. The rms disagreement between the table and what this formula computes is 0.01 V/V and the largest disagreement is -0.044 V/V at 37 °F and 19 psig where the dissolved level is 3.27 volumes.

The table data do not exactly conform with what the physics predict and so it is not possible to fit it much better than that though slightly better agreement can be had with a 3rd order polynomial fit. Going to higher orders doesn't gain much and with the polynomial fits one dare not go outside the boundaries of the table (not that one would necessarily want to do that anyway). The exponential form is more robust in this regard.

Polynomial fits and a broader look at the whole subject can be found at
http://www.wetnewf.org/pdfs/Brewing_...%20Volumes.pdf

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