Carbonation under pressure
Pressure for target CO₂ saturation at a given temperature.
In a keg, beer is carbonated with pressure: CO₂ dissolves more readily the higher the pressure and the lower the temperature. The calculator shows what pressure to set on the regulator for the saturation you want.
Calculator
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What CO₂ volumes mean
Saturation is measured in volumes: one volume means that one litre of CO₂ at standard conditions is dissolved in a litre of beer. Lagers are usually carbonated to 2.4–2.7 volumes, English ales to 1.5–2.0, and wheat beers and Belgian strong ales to 3.0–4.0.
Some of the gas is already in the beer: after fermentation at atmospheric pressure about 0.8–1.0 volume remains, and that amount depends on the fermentation temperature. Only the difference between the target and this residual needs to be added.
How pressure is calculated
Gas solubility is proportional to absolute pressure (Henry’s law), so the calculation comes down to one multiplication: the residual saturation is multiplied by the ratio of absolute pressure to atmospheric. The calculator solves the inverse problem — finding the pressure for a target saturation.
The solubility curve comes from M. Hall’s “Brew by the Numbers”; the same curve is used for priming calculations, so both carbonation methods give a consistent result.
carbonation = residual · (Pabs / 1.01325 bar)
Target saturation by style
| Style | CO₂ volumes |
|---|---|
| English bitter | 1.5–2.0 |
| American IPA | 2.2–2.6 |
| Lager | 2.4–2.7 |
| Belgian strong ale | 2.8–3.2 |
| Wheat beer | 3.3–4.0 |
Things to keep in mind
- A regulator gauge reads gauge pressure; the calculation uses absolute pressure, that is, gauge plus atmospheric.
- Warm beer needs noticeably more pressure: at 20 °C, 2.4 volumes require about 1.8 bar; at 5 °C, about 0.7 bar.
- Equilibrium does not arrive at once: with the keg shaken and carbonation pressure applied it takes hours, with passive saturation it takes days.
- If the target is below the residual CO₂ content, pressure cannot get you there — that gas has to be removed with a vacuum or by prolonged agitation.