How to Force Carbonate a Keg (PSI Chart + 3 Methods)
Three force carbonation methods compared, plus a computed PSI chart for 34-50°F at 2.0-3.2 volumes. Set-and-forget: 5-14 days. 30 psi burst: 24-36 hours.
To force carbonate a keg, chill the beer to 38°F, set your CO2 regulator to the pressure that matches your target carbonation, and leave it connected. At 38°F, 11.2 psi gives 2.5 volumes of CO2 and 12.3 psi gives 2.6 volumes. Equilibrium takes 5 to 14 days with the gas simply left on. If you need it faster, 30 psi for 24 to 36 hours gets you there, but you must vent the keg and drop to serving pressure at the end or the beer keeps climbing toward 4.3 volumes. Rolling the keg on its side with the gas at 30 psi carbonates in 3 to 8 minutes of active agitation and is the easiest way to ruin a batch.
The three methods, with honest trade-offs
Set-and-forget at serving pressure (5-14 days)
Chill the keg to serving temperature, hook up gas at the pressure from the chart below, and walk away. Nothing else happens. CO2 dissolves until the beer reaches equilibrium with the headspace, and because the regulator is already at serving pressure, the beer is balanced the moment it is ready. A 5-gallon corny keg at 38°F and 12 psi is drinkable at roughly day 5 and fully at equilibrium by day 10 to 14. Cold beer and more headspace surface area speed this up; a keg laid on its side gains surface area and shaves a couple of days. This is the only method with no overshoot risk, because the beer cannot exceed the volume that pressure supports. Use the keg carbonation calculator to get the exact psi for your temperature and target.
The 30 psi burst (24-36 hours)
Set the regulator to 30 psi, leave the keg cold and undisturbed for 24 to 36 hours, then disconnect gas, pull the pressure relief valve until the keg hisses down to atmospheric, and reconnect at serving pressure. The high pressure gradient drives CO2 in about 8 to 10 times faster than serving pressure alone. The risk is arithmetic: 30 psi at 38°F has an equilibrium point of 4.31 volumes, which is up in Berliner Weisse and Weizen territory (3.3-4.5 volumes in the table above) — nowhere near an ale target of 2.4. At 24 hours you are typically at 2.4 to 2.8 volumes; at 72 hours you are badly over. Set a timer, not a reminder. If you overshoot, vent the keg fully, wait 12 hours at serving pressure, and repeat until it tastes right.
The shake method (3-8 minutes)
Chill the keg, set 30 psi, lay it on its side, and rock it until the hissing of gas absorbing into the beer stops, usually 3 to 8 minutes of active agitation. Then vent, drop to serving pressure, and let it settle cold for 12 to 24 hours before pouring. It works, and it is the fastest option, but there is no feedback loop: you cannot un-dissolve CO2 quickly, agitation warms the beer and stirs up sediment, and the beer pours as foam for hours afterward. Most brewers who shake once end up over 3.0 volumes on an ale that wanted 2.4. Reserve it for the night before a party.
Force carbonation PSI chart
Every cell below is computed from the standard force-carbonation regression used across homebrewing software, where P is gauge pressure in psi, T is beer temperature in °F, and V is dissolved CO2 in volumes:
P = −16.6999 − 0.0101059·T + 0.00116512·T² + 0.173354·T·V + 4.24267·V − 0.0684226·V²
| Beer temp (°F) | 2.0 vol | 2.4 vol | 2.5 vol | 2.8 vol | 3.2 vol |
|---|---|---|---|---|---|
| 34 | 4.3 | 8.2 | 9.2 | 12.1 | 16.0 |
| 36 | 5.1 | 9.2 | 10.2 | 13.3 | 17.3 |
| 38 | 6.0 | 10.2 | 11.2 | 14.4 | 18.6 |
| 40 | 6.8 | 11.2 | 12.3 | 15.5 | 19.8 |
| 42 | 7.7 | 12.2 | 13.3 | 16.7 | 21.1 |
| 44 | 8.6 | 13.2 | 14.4 | 17.8 | 22.4 |
| 46 | 9.5 | 14.2 | 15.4 | 19.0 | 23.7 |
| 48 | 10.4 | 15.3 | 16.5 | 20.1 | 25.0 |
| 50 | 11.3 | 16.3 | 17.6 | 21.3 | 26.3 |
All values are psi gauge at sea level. Two things fall out of the table immediately. First, temperature matters more than most brewers assume: holding 2.5 volumes costs 9.2 psi at 34°F but 17.6 psi at 50°F, a 91 percent increase over 16 degrees. Second, a warm keg at a cold-keg pressure will be undercarbonated forever, no matter how long you wait. Measure the beer temperature, not the air in the kegerator, and give a freshly moved keg 24 hours to equalize before you trust the number. For temperatures and volumes between the rows here, run them through the keg carbonation calculator rather than interpolating by eye, since the T·V cross term makes the surface slightly non-linear.
CO2 volumes by style
Volumes of CO2 means the volume of gas dissolved per volume of beer at standard conditions. These ranges track the BJCP style descriptions and standard brewing references.
| Style family | Volumes CO2 | psi at 38°F |
|---|---|---|
| British ales, cask-conditioned bitter, mild | 1.5-2.0 | 0.7-6.0 |
| Porter, stout (non-nitro) | 1.7-2.3 | 2.8-9.1 |
| American ales, IPA, pale ale | 2.2-2.7 | 8.1-13.3 |
| American lager, pilsner, Kölsch | 2.4-2.7 | 10.2-13.3 |
| Belgian ales, saison, tripel | 2.7-3.4 | 13.3-20.6 |
| German wheat beer, Berliner Weisse | 3.3-4.5 | 19.6-31.9 |
Anything above roughly 2.8 volumes will not pour through a standard kegerator faucet without foaming unless the line is lengthened or the beer is served through a longer, colder run. If you are bottling instead of kegging, the same volume targets apply, but the sugar math is different: run them through the priming sugar calculator, which accounts for the residual CO2 already in solution at your highest fermentation temperature.
Line balancing so it actually pours right
Carbonation and dispense are separate problems that get blamed on each other. A balanced system is one where line resistance cancels keg pressure, leaving about 1 psi at the faucet and a pour rate near 2 ounces per second, or a 12-ounce glass in roughly 6 seconds.
The published design figure for 3/16-inch ID vinyl beer line is 3.0 psi of resistance per foot, though real tubing is rated anywhere from 1 to 3 psi per foot depending on formulation. Using length = (serving psi − 1) ÷ 3.0, a 12 psi system computes to (12 − 1) ÷ 3.0 = 3.7 feet — which is why kits ship with short 4-5 foot lines.
In practice most brewers find 5 feet pours too fast and foams. The reason is that soft vinyl at cold temperature and low flow behaves closer to 1.2-1.4 psi per foot than the catalog 3.0. Recompute at 1.3 psi per foot and the same 12 psi system wants (12 − 1) ÷ 1.3 = 8.5 feet. That is the practical answer: 8 to 10 feet of 3/16-inch line for a 10-14 psi system. Line is cheap, roughly $1 per foot, so cut long and trim an inch at a time until the pour takes about 6 seconds. Add 0.5 psi of resistance for every foot the faucet sits above the keg, which is typically 2 to 3 feet in a converted chest freezer with a collar.
Troubleshooting the two classic failures
Flat beer
Either the CO2 never got in or it leaked out. Check the gas side first: spray a 50/50 water and dish soap mix on every fitting, the lid gasket, and both posts, and watch for bubbles for 30 seconds. A pinhole leak drains a 5-pound CO2 tank in a week and holds the keg at a fraction of the indicated pressure. If the tank is holding, the answer is usually time. Beer at 12 psi and 38°F takes 10 to 14 days to reach 2.57 volumes without agitation, and brewers routinely give up on day 4. Confirm the gas post is fully seated, confirm the beer is actually at 38°F and not 48°F, and wait another week. Warm beer is the most common silent cause: at 48°F, 12 psi only supports about 2.1 volumes.
Foamy pours
Three causes, in order of frequency. Too-short line, fixed by going to 8-10 feet as above. Too-warm beer or too-warm line, fixed by getting the entire run into the cold space, since a 6-foot line sitting at room temperature will break CO2 out of solution regardless of length. Over-carbonation, fixed by disconnecting gas, venting through the PRV, and repeating every few hours at serving pressure until the beer settles; each full vent cycle drops roughly 0.2 to 0.4 volumes. Also check for a partially open faucet, which foams at any pressure, and a scratched or worn beer line, which nucleates bubbles along the scratch.
Safety
Standard 5-gallon ball-lock Cornelius kegs are rated to 130 psi maximum working pressure. That rating is not permission to run anywhere near it: even the highest carbonation target in the style table above needs only 31.9 psi, and nothing in normal force carbonation should exceed 30 psi.
Always run a working pressure relief valve in the lid. Aftermarket PRVs are sold at specific set points — 10 psi and 17 psi for pressure fermentation, 35 psi and 60 psi for kegging — while the standard factory pull-ring lid valve is rated around 100 psi. Check the set point printed on yours before running a 30 psi burst: a 10 or 17 psi spunding PRV will vent the burst straight back out of the lid. Test yours by pulling the ring occasionally; a PRV gummed shut with dried beer is worse than no PRV, because you will assume it is protecting you. Never leave a keg connected to an unregulated CO2 cylinder, never use a tank without a regulator, and store CO2 cylinders upright and secured. A 5-pound CO2 tank at room temperature holds roughly 800 psi.