Draught Operations > A Matter of Balance > Carbonation Dynamics
Beer carbonation responds to changes in storage and serving conditions. Let’s consider an average keg with a carbonation of 2.5 volumes of CO2 and see what happens when conditions change.
Beer temperature and the CO2 pressure applied through the coupler influence the amount of CO2 dissolved in any keg of beer. At any temperature, a specific pressure must be applied to a keg to maintain the carbonation established by the brewery. If temperature or pressure varies, carbonation levels will change. Here’s an example.
Beer in a keg at 38°F needs a pressure of 11 psi to maintain 2.5 volumes of CO2 as the beer is served. So long as the temperature and pressure remain constant, the beer maintains the same carbonation level.
| CO2 Pressure |
| Temp |
9 psi |
11 psi |
13 psi |
| 34 °F |
2.5 |
2.7 |
2.9 |
| 38 °F |
2.3 |
2.5* |
2.7 |
| 42 °F |
2.1 |
2.3 |
2.5 |
| * Pressures rounded for purposes of illustration. Do not use these charts for system adjustment. |
If the temperature of the beer changes, so does the required internal keg pressure. Here we see that if the pressure remains at 11 psi but the temperature of the beer rises to 42°F, carbonation will begin to move from the beer to the headspace. Over a few days and as the keg empties, the overall carbonation in the beer drops to 2.3 volumes of CO2.
| CO2 Pressure |
| Temp |
9 psi |
11 psi |
13 psi |
| 34 °F |
2.5 |
2.7 |
2.9 |
| 38 °F |
2.3 |
2.5* |
2.7 |
| 42 °F |
2.1 |
2.3 |
2.5 |
Alternately, if the temperature remains at 38°F, but the CO2 pressure increases to 13 psi, then the carbonation level of the beer in the keg will increase as the beer slowly absorbs additional CO2.
| CO2 Pressure |
| Temp |
9 psi |
11 psi |
13 psi |
| 34 °F |
2.5 |
2.7 |
2.9 |
| 38 °F |
2.3 |
2.5* |
2.7 |
| 42 °F |
2.1 |
2.3 |
2.5 |
The “ideal gauge pressure” for a beer is the pressure at which CO2 is not diffusing from beer into the headspace and excess CO2 is not absorbing in the beer. This value varies from account to account depending upon factors such as temperature, altitude and carbonation level of the beer. Because beer carbonation can vary with the temperature of your cooler and the pressure applied to the keg, you must take care to maintain steady values suited to your system and beers.
You can determine ideal gauge pressure for pure CO2 from the chart shown in the table below and in Appendix B. If you do not know the carbonation level in the beer, you can estimate it using the procedure found in Appendix B.
| Determination of CO2 application pressure given volumes of CO2 and temperature |
| Vol CO2 |
2.1 |
2.2 |
2.3 |
2.4 |
2.5 |
2.6 |
2.7 |
2.8 |
2.9 |
3.0 |
3.1 |
| Temp. °F |
PSI |
PSI |
PSI |
PSI |
PSI |
PSI |
PSI |
PSI |
PSI |
PSI |
PSI |
| 33 |
5.0 |
6.0 |
6.9 |
7.9 |
8.8 |
9.8 |
10.7 |
11.7 |
12.6 |
13.6 |
14.5 |
| 34 |
5.2 |
6.2 |
7.2 |
8.1 |
9.1 |
10.1 |
11.1 |
12.0 |
13.0 |
14.0 |
15.0 |
| 35 |
5.6 |
6.6 |
7.6 |
8.6 |
9.7 |
10.7 |
11.7 |
12.7 |
13.7 |
14.8 |
15.8 |
| 36 |
6.1 |
7.1 |
8.2 |
9.2 |
10.2 |
11.3 |
12.3 |
13.4 |
14.4 |
15.5 |
16.5 |
| 37 |
6.6 |
7.6 |
8.7 |
9.8 |
10.8 |
11.9 |
12.9 |
14.0 |
15.1 |
16.1 |
17.2 |
| 38 |
7.0 |
8.1 |
9.2 |
10.3 |
11.3 |
12.4 |
13.5 |
14.5 |
15.6 |
16.7 |
17.8 |
| 39 |
7.6 |
8.7 |
9.8 |
10.8 |
11.9 |
13.0 |
14.1 |
15.2 |
16.3 |
17.4 |
18.5 |
| 40 |
8.0 |
9.1 |
10.2 |
11.3 |
12.4 |
13.5 |
14.6 |
15.7 |
16.8 |
17.9 |
19.0 |
| 41 |
8.3 |
9.4 |
10.6 |
11.7 |
12.8 |
13.9 |
15.1 |
16.2 |
17.3 |
18.4 |
19.5 |
| 42 |
8.8 |
9.9 |
11.0 |
12.2 |
13.3 |
14.4 |
15.6 |
16.7 |
17.8 |
19.0 |
20.1 |
| * Chart assumes sea-level altitudes. Add 1 psi for every 2,000 ft. above sea level. |
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