Kegging is packaging your finished beer in a pressurised keg and carbonating it with a CO2 tank, instead of adding priming sugar and filling bottles. It swaps a two-hour bottling day and three weeks of conditioning for a 15-minute transfer and carbonated beer in days.
Why keg instead of bottle?
Bottling is where a lot of homebrewers lose their enthusiasm. Every bottle has to be cleaned, sanitised, filled, and capped, then the whole batch sits for two to three weeks while priming sugar slowly ferments in the bottle. Kegging collapses all of that into one vessel and one gas connection.
You also gain control. Carbonation level is a dial you turn, not a fixed dose of sugar you commit to before you know how the beer tastes. Under-carbonated? Add pressure. Too lively? Vent and drop it. And because the beer lives under CO2 the whole time, a kegged beer that’s been properly purged keeps its fresh, hop-forward character far longer than the same beer in bottles.
The corny keg system: ball-lock vs pin-lock
The standard homebrew keg is a 5-gallon Cornelius keg — “corny” for short — originally built to hold soda syrup for restaurants. Each has a lid with a pressure relief valve, a gas-in post that feeds the top of the keg, and a liquid-out post connected to a long dip tube that reaches the bottom. Push gas in the top, beer comes out the bottom.
They come in two families that are almost identical inside but use different connectors:
For most people starting out, ball-lock is the safer choice: more kegs, more spare parts, more o-ring kits, and more tutorials assume it.
CO2 tank, regulator, and disconnects
The gas side is what carbonates and dispenses the beer. It’s three parts in a line: a CO2 cylinder, a regulator that steps the tank’s very high pressure down to a usable serving pressure, and the disconnects that clip onto the keg posts.
To carbonate, you connect only the gas disconnect. To pour, gas stays on the gas post holding pressure while beer pushes out through the liquid post. Keep a little gas pressure on the keg at all times once it’s carbonated, or the beer slowly goes flat.
Transferring beer and purging the air
Oxygen is the one thing that ruins finished beer — it turns fresh, bright flavours stale and cardboardy within weeks. The goal of a good transfer is to move beer into the keg while keeping air away from it.
- 1Pre-purge the empty keg Seal the clean, sanitised keg empty, connect CO2, and pull the pressure relief valve a few times to flush the air out. Better still, fill the keg with sanitiser and push it out with CO2 so the keg fills with gas as the liquid leaves — now the beer arrives into a CO2 atmosphere, not air.
- 2Rack cold beer gently Siphon or closed-transfer the beer from your fermenter into the keg, ideally leaving the yeast and trub behind. Cold beer picks up less oxygen and holds CO2 better, so chill first if you can.
- 3Seal and purge the headspace Fit the lid, apply 20–30 psi briefly to seat the lid seal, then pull the relief valve several times — each vent-and-refill cycle replaces oxygen-rich headspace with pure CO2.
- 4Check for leaks Spray connections and the lid with sanitiser or soapy water — creeping bubbles mean a leak. A leaking keg will never hold carbonation and will drain your CO2 tank overnight.
Related calculator
Beer Carbonation & Priming Sugar Calculator
Calculate how much priming sugar to add for bottle conditioning — supports corn sugar, table sugar, DME, and honey with target CO₂ volumes.
Two ways to carbonate: set-and-forget vs burst
Once beer is in a sealed, purged keg, carbonating just means holding it under CO2 pressure until the gas dissolves into the beer. There are two common approaches, trading speed for control.
A reliable middle path: burst at 30 psi for 24 hours to get most of the way there, then set the regulator to serving pressure and let it finish over a couple of days. You get speed without the guesswork of pulling it off gas at exactly the right moment.
Temperature, PSI, and volumes of CO2
Carbonation is measured in “volumes of CO2” — how many times the beer’s own volume in dissolved gas it holds. The pressure needed to reach a target volume depends on temperature: colder beer absorbs CO2 more readily, so it needs less pressure; warmer beer needs more. That’s why a carbonation chart is keyed to both.
For a typical 2.4–2.5 volumes (most ales and lagers), at common serving temperatures:
Match the pressure to your beer’s actual temperature, not the room’s. Target volume also varies by style — dial the pressure to hit the range the style calls for:
Cleaning and sanitising kegs
A keg is reused batch after batch, so cleaning it properly is what keeps your beer clean. There are two distinct jobs: cleaning removes soil and residue, sanitising kills what’s left before beer goes in.
- 1Break it down and soak Remove the lid, both posts, poppets, and dip tubes. Soak the parts and fill the keg with a warm alkaline brewery wash (PBW or similar) for 20–30 minutes to lift beer stone and residue.
- 2Scrub and rinse Use a keg brush on the interior, clean the posts and dip tubes, and rinse everything thoroughly with clean water so no cleaner remains.
- 3Inspect the o-rings Check the lid, post, and dip-tube o-rings. Cracked, flat, or beer-stained rings cause leaks and off-flavours — replace them cheaply and periodically rather than chasing mystery leaks later.
- 4Sanitise last Reassemble, fill with a no-rinse sanitiser like Star San, seal, and push it through the liquid and gas posts so sanitiser touches every surface beer will. Push the sanitiser out with CO2 right before filling and the keg is purged and ready in one move.
Watch for
- Never store a keg wet and sealed — trapped moisture breeds mould and infection
- Do not skip disassembling the posts — beer residue hides under the poppets
- Old, hard, or discoloured o-rings are the number-one cause of leaks and stale beer
- Avoid bleach or harsh chlorine cleaners — they pit stainless steel and harbour off-flavours
Keg to tap: the full sequence
Putting it all together, here’s the order of operations from finished fermenter to first pour.
- 1Confirm fermentation is finished Stable hydrometer readings across two or three days at your expected final gravity. Kegging active beer over-carbonates and can build dangerous pressure.
- 2Clean and sanitise the keg Full breakdown, alkaline soak, rinse, o-ring check, then sanitise. Leave sanitiser in until transfer time.
- 3Purge and transfer Push the sanitiser out with CO2 so the keg fills with gas, then rack the cold beer in gently, leaving trub behind.
- 4Seal and purge headspace Fit the lid, hit 20–30 psi to seat it, then pull the relief valve several times to flush oxygen from the headspace. Leak-check.
- 5Carbonate Set-and-forget at 10–12 psi for 1–2 weeks, or burst at 30 psi for 24–48 hours, then drop to serving pressure.
- 6Serve Keep the keg cold with serving pressure on the gas post, connect the liquid disconnect to your tap, and pour. Discard the first cloudy pour if any dip-tube sediment carried over.
That’s the whole cycle. After the first batch the gear is set, and every future kegging day is really just clean, purge, transfer, and dial in the pressure.
