# Residual CO2 from fermentation as a function of altitude

I'm looking for a graph or table (preferably in metric values) that shows the amount of residual carbonation after fermentation under ambient pressure as a function of atmospheric pressure and/or altitude under constant temperature.

I've googled extensively but all I've been able to find are graphs and tables that show residual CO2 as a function of temperature under constant pressure (usually 1 atmosphere).

Can anyone point me into the right direction? Tnx!

There actually is a simple formula that can be applied to this:

Vr = 4.85 * Pa / 12.4 * T

Where:

Vr = Volumes of CO2

Pa = Absolute pressure, in PSI

T = Temperature, in degrees F

You'd just need to use a tool like this to calculate the absolute pressure at your particular altitude.

Equation is from this book

edit

I should also note this equation can be used to find the equilibrium carbonation level in any situation the pressure and temperature are known, i.e. low-and-slow force carbonation, draught line balancing etc.

You just need to make sure to use the absolute pressure, which in this case will be atmospheric pressure plus gauge pressure

• THAT is what I was looking for! Thank you so much! – Frank van Wensveen Jun 8 '17 at 9:18
• This was really helpful thanks! From the formula, and with -1 psi per 2000 feet, I figure 5000ft (salt lake city about) is approximately the same as 1 deg F warmer. Or iow very little difference. – vontrapp Jan 17 '18 at 4:56

Here's some resources on some carbonation basics. I too have not seen a chart made for residual cO2 but would be a great tool if someone made it. However most of it has been done by force carbonation charts just need to account for the atmophere pressure.

http://www.winning-homebrew.com/support-files/kegcarbonationchart.pdf

https://en.m.wikipedia.org/wiki/Atmospheric_pressure

http://www.draughtquality.org/wp-content/uploads/2012/02/Carbonation_PH-Final_1.pdf "Add 1 PSI for each 2,000 in feet elevation" for force carbonation.

The residual cO2 in beer from fermentation is associated to elevation. As it retains the cO2 volumes not allowed to escape by atmospheric pressure.

Some real advantages to knowing this is because cO2 is toxic to yeast. Yeast in theory would have an easier time at higher altitudes. Though may have a harder time during aerobic stage.

Also beer kegged at low altidude then poured at high altitude will have more of perceived cO2 volumes. Even though the volumes are the same kegged at high or low because of the closed system. With proper force carbonation.

The 1 PSI boost needed per 2k feet is only to adjust for accurate reading of the pressure gauge. Not because it takes more cO2 at higher altitude to achieve x volumes.

Edit / update http://beerandwinejournal.com/residual-co2/ I believe force carb charts already consider residual cO2. So by comparing the two sets of data we can calc what you need. Beer at 50F 1 ATM has 1.15 cO2 volumes and needs 11.3 psi at 1 ATM (sea level) for 2.0 cO2 volumes. We see that it takes 12.5 psi to get 2.1 volumes (1.2 psi increase to get +0.1 volumes). So without doing the exact math the residual c02 at say 2400 feet would be 1.25 for 50F beer. Now the base formulas are more complex but this should be a good start for someone to make a graph or calculator. Keep in mind that the residual co2 will be based on the highest temp a beer has ever reached after fermentation.

• Useful info, and thanks for the reply, but this is not what I asked. :-) I specifically need to know the effect altitude (i.e. atmospheric pressure) on residual CO2 after fermentation under ambient pressure. – Frank van Wensveen May 26 '17 at 9:21
• @FrankvanWensveen found some charts on residual co2 and updated – Evil Zymurgist May 26 '17 at 13:03
• As noted elsewhere, the force carb charts are correcting for gage reading, not for residual co2. Residual co2 is irrelevant for forced carbonation and here's why: for bottle carbonation, total co2 in the bottle is equal to the residual co2 plus the co2 from the added sugar. Residual + priming -> total co2 -> pressure -> dissolved co2. When force carbonating, you skip straight to pressure by a regulator: pressure (regulated) -> dissolved co2. Residual is not a factor in the latter. – vontrapp Jan 17 '18 at 4:52