Kegging, Carbonation & Competition Bottles

The brew-day walkthrough covers bottling. Kegging is the other route: faster than bottle conditioning, reusable, and much kinder on the beer because you can keep oxygen away from it throughout.

It does create one problem specific to competitions, though — almost every comp wants bottles, so at some point a kegging brewer has to get beer back into glass without undoing all that careful oxygen management. That section is at the end, and it is the part most worth reading before an entry deadline.

Carbonation, measured

Carbonation is dissolved CO₂, measured in volumes (litres of gas per litre of beer). Cold beer holds more CO₂ than warm, so carbonation is always a relationship between pressure and temperature — the same psi gives different carbonation at different temperatures. Use a carbonation chart.

Force carbonation

Slow method (recommended, 2–3 weeks). Set the regulator to your serving pressure for the style and temperature, connect gas, wait. Gentle on seals, hard to overshoot, and it lands at exactly serving pressure with no rebalancing.

Fast method (5–7 days). Hold at ~30–35 psi, optionally rocking the keg. Quicker, but you must drop back to serving pressure and vent the excess before pouring or it foams.

There is a quality reason to prefer the slow route beyond just being safer. Carbonation forced in quickly tends to drink coarse and prickly — the CO₂ has not had time to settle into equilibrium with the beer, and the result is aggressive, spiky bubbles rather than the fine, integrated condition you get from a slow carbonation on a well-conditioned beer. That difference matters more than people expect, because carbonation is what carries aroma to the back of the nose. Coarse CO₂ amplifies everything, including any small fault sitting quietly in the background.

Either way, chill the keg first. CO₂ dissolves far better cold, and the carbonation pressure is set for the serving temperature.

Keep oxygen out

Oxygen is what turns good beer into cardboard. Kegging’s advantage is that you can exclude it:

1. Purge the keg before filling — fill the sanitised keg with CO₂, pressurise to ~2 psi and vent, three times
2. Closed transfer — rack into the keg through the liquid post and diptube so beer fills from the bottom up under CO₂ rather than splashing through air. Pre-purge, release all pressure before connecting, prime the line so beer is first in, and crack the relief valve so displaced CO₂ can escape
3. Keg hopping — add hops before the purge, so the purge clears the oxygen around them

Safety: never seal a keg on beer that has not finished fermenting. Residual fermentation in a sealed keg builds dangerous pressure, especially if a diptube or relief valve clogs with hop debris. Confirm terminal gravity first — and if the beer was heavily dry hopped, read Diacetyl & hop creep before you trust that reading.

Filling and a weight trick

Fill to about an inch from the top. The tidy way to hit a target volume is by weight: tare the empty keg, then fill to a target total. A Kegland corny (empty tare ~4.25 kg) filled to ~23.25 kg gives roughly 19 L.

Bottle conditioning vs kegging

Bottling carbonates by feeding yeast a measured priming sugar dose in the sealed bottle. Kegging carbonates with gas under pressure. Same destination — kegging just gives you a dial instead of a one-shot calculation.

If you bottle exclusively, most of this guide still matters for the carbonation targets; the oxygen sections apply at your bottling bucket instead.

Filling competition bottles off a keg

This is where members lose points on beer that was fine in the keg. A carelessly filled entry bottle can arrive oxidised, under-carbonated, or carrying sanitiser residue — and the judge has no way of knowing the keg version was excellent.

Fill cold and slow. Cold beer holds its CO₂ and foams less. Take the keg down to serving temperature or below, and drop the regulator to 2–5 psi for filling. Pouring at full serving pressure through a short line is how you get a glass of foam and a flat bottle.

Purge the bottle. Fill the empty bottle with CO₂ before the beer goes in, or fill from the bottom with a wand or beer gun so beer displaces air upward rather than splashing through it.

Purge the fill line. After sanitising, blow the line clear with CO₂ before the first bottle. Sanitiser residue goes into the first bottles filled — which are very often the ones you send away. This is covered in detail in Bandaid, TCP & Clove, and it is the single most common way a comp entry picks up a fault the rest of the batch does not have.

Cap on foam. Let the beer foam gently at the neck and cap through it, so the headspace is CO₂ rather than air. A small amount of foam at capping is worth far more than a tidy fill.

Fill more than you need. Most comps want two or three bottles per entry. Fill a couple extra and open one yourself a few days later — that is your check that the fill worked, and it is much better to find a problem in your kitchen than on a scoresheet.

Timing. Fill close to the entry deadline rather than far ahead. A bottle filled off a keg is not bottle conditioned, so there is no yeast in there to scavenge oxygen, and nothing improves in the interim. For hoppy beer especially, every week between filling and judging costs you aroma.

Troubleshooting

• Won’t hold pressure — leak. Soapy water on every post and connection; replace worn O-rings
• Flat after force carbonating — keg lost pressure; re-pressurise and wait
• Too foamy — pressure too high, or beer too warm. Reduce by 2–3 psi, vent, wait 48 h, and check your serving line length
• Stale or cardboard — oxygen got in during transfer. Tighten the purge and use a closed diptube transfer next time
• Bottles flat but the keg is fine — filled too warm, too fast, or without purging. See the competition section above

See also: Pressure Fermentation for pushing beer to a keg straight from the fermenter, and Cleaning & Sanitation for keg and line care.