Bottling day checklist

Q: How do you know when beer is ready to bottle?

Take hydrometer readings 2–3 days apart. If the gravity is stable and in the expected range for the recipe, fermentation is done and the beer is safe to bottle. Bottling while gravity is still dropping is the most common cause of bottle bombs.

Q: How much headspace should you leave in beer bottles?

About 1 inch (2–3 cm) from the top of the bottle. A bottling wand leaves roughly the right headspace automatically when you fill to the brim and remove it.

Q: What should you do if your bottles are over-carbonated?

Chill them cold — cold beer holds CO2 better — then open carefully, pointed away from people, ideally outdoors or over a sink. If caps are bulging or bottles gush violently, consider dumping the batch rather than risking an explosion.

Bottling is simple but unforgiving: nearly every ruined batch and every bottle bomb traces back to skipping a step here. Work the list in order.

⚠ The one rule that matters

Do not bottle until fermentation is finished — confirmed by a stable hydrometer reading over 2–3 days, not by the airlock, not by the calendar. Bottling early is the #1 cause of exploding bottles.

Confirm it's done. Stable gravity over 2–3 days, in the recipe's expected range. If it's still dropping, wait.
Calculate priming sugar. Use the priming sugar calculator with your batch size, style, and the coldest temp the beer reached. Weigh it on a scale — don't scoop by volume.
Sanitize everything. Bottles, caps, bottling bucket, racking cane, tubing, wand. Star San or iodophor, proper contact time, no shortcuts.
Dissolve the sugar. Boil the priming sugar in 2 cups of water for 5 minutes, cover, and cool it. Pour it into the bottling bucket first.
Rack gently onto the sugar. Siphon the beer onto the cooled sugar solution with the tube below the surface. No splashing — oxygen at this stage stales beer fast. A gentle stir with a sanitized spoon mixes it evenly.
Fill to ~1 inch of headspace. A bottling wand filled to the brim leaves about the right headspace when removed. Cap immediately.
Condition warm. Store bottles around 70°F (21°C) for 2–3 weeks. Yeast carbonates slowly when cold.
Chill before opening. 24–48 hours in the fridge lets CO₂ dissolve fully into the beer instead of foaming out.

Signs of trouble

Gushers — beer foams violently on opening. Often over-carbonation or infection.
Bulging caps — pressure is building beyond normal. Chill immediately and handle with care.
One bottle explodes — treat the whole batch as suspect. Chill everything cold, open bottles pointed away from people (outdoors is best), and seriously consider dumping rather than risking injury.

Causes, in order of likelihood: bottling before fermentation finished, too much priming sugar (measured by volume instead of weight), or an infection that kept fermenting in the bottle.

Frequently asked questions

How do you know when beer is ready to bottle?

Stable hydrometer readings 2–3 days apart, in the expected range. Not the airlock, not the calendar.

How much headspace should you leave in beer bottles?

About 1 inch (2–3 cm). A bottling wand filled to the brim leaves roughly the right amount when removed.

What should you do if your bottles are over-carbonated?

Chill them cold, open carefully pointed away from people, ideally outdoors. Bulging caps or violent gushers across the batch mean you should consider dumping it — no beer is worth an injury.