🫧 Bottling, Kegging & Carbonation

Fermentation is finished, your hydrometer readings are steady, and the beer tastes good — but flat. The final step is getting it into bottles or kegs and giving it the right amount of fizz. Carbonation is not just decoration: it lifts aroma, sharpens flavour, shapes mouthfeel and builds the foam head.

Understanding Carbonation

Carbonation is measured in volumes of CO₂ — the volume the dissolved gas would occupy at standard conditions, relative to the volume of beer. A beer with 2.5 volumes holds 2.5 litres of CO₂ per litre of beer.

Keep in mind that some CO₂ is already dissolved after fermentation, and how much depends on the beer’s highest temperature after fermenting. Priming calculators account for this.

Bottle Conditioning

The classic homebrew method is bottle conditioning: add a measured dose of sugar at bottling, and the remaining yeast ferments it inside the sealed bottle, producing CO₂ that dissolves into the beer.

How to Bottle

1. Confirm fermentation is complete — stable gravity readings over several days.
2. Clean and sanitise bottles, caps, bottling bucket, siphon and wand.
3. Prepare priming sugar — dissolve it in a small amount of boiling water, then cool.
4. Combine gently — add sugar solution to the bucket and siphon beer onto it with minimal splashing to avoid oxidation.
5. Fill and cap — leave about 2–3 cm of headspace.
6. Condition warm — around 18–22 °C for two to three weeks.
7. Chill for a few days before drinking so CO₂ settles into solution.

Priming Sugar Options

• Corn sugar (dextrose) — the standard; roughly 100–130 g per 19 L for typical ales
• Table sugar (sucrose) — works fine; use slightly less than dextrose
• Dry malt extract — adds subtle maltiness; use more by weight
• Carbonation drops — pre-measured tablets, one or two per bottle

Always use a priming calculator based on your volume, temperature and target carbonation.

Safety: Avoiding Bottle Bombs

Over-carbonated bottles can burst violently and throw glass. Prevent it by:

• Never bottling before fermentation is finished
• Measuring priming sugar accurately and mixing it evenly
• Using sturdy, pressure-rated bottles — avoid thin twist-off bottles
• Keeping good sanitation, as infections can keep eating sugar long after bottling
• Storing conditioning bottles in a covered box, away from people

If bottles gush or feel dangerously firm, chill them immediately to slow the yeast, and handle them with gloves and eye protection.

Kegging

Kegging skips bottle conditioning entirely. Beer is transferred to a stainless steel keg (commonly a 19 L “Corny” keg) and carbonated with pressurised CO₂ from a cylinder.

Benefits

• One vessel to clean instead of 50 bottles
• Carbonation in days rather than weeks
• Precise control over fizz
• Less sediment and oxidation risk if done well

Carbonation Methods

• Set and forget — Chill the keg, set the regulator to the pressure matching your target volumes and temperature (for example around 10–12 psi at 4 °C for ~2.5 volumes), and wait about a week to ten days.
• Burst carbonation — Use higher pressure for a day or two, then drop to serving pressure. Faster but easier to overshoot.

Consult a carbonation chart for exact pressure–temperature pairings.

Kegging Safety

• Use a regulator — never connect a CO₂ cylinder directly to a keg
• Check that kegs have working pressure-relief valves
• Secure cylinders upright so they cannot fall
• Test for leaks with soapy water
• Ventilate: CO₂ can build up in small, enclosed spaces like keezers or closets

Bottling from a Keg

Want to share kegged beer? A counter-pressure filler or a simple beer gun lets you fill bottles from a carbonated keg while limiting foam and oxygen pickup.

Troubleshooting

Key Takeaways

• Carbonation is measured in volumes of CO₂ and varies by style
• Bottle conditioning uses a precise dose of sugar and patience
• Kegging is faster and more controllable, but requires careful handling of pressurised gas
• Never bottle unfinished beer