What causes bottle bombs?

Bottle bombs occur when total CO2 pressure exceeds what the bottle can withstand. This happens from: bottling before fermentation is complete (residual sugar ferments in the bottle), adding too much priming sugar, or infection with wild yeast that ferments sugars your brewing yeast cannot.

How do I know fermentation is really finished?

Take hydrometer readings on 3 consecutive days. If the reading is identical (within 0.001), fermentation is complete. Do not rely on airlock activity — it can stop while fermentable sugars remain. Always verify with a hydrometer.

What is the maximum safe CO2 for glass bottles?

Standard 330ml and 500ml crown cap bottles are rated to approximately 3.0 volumes CO2. Belgian-style bottles (thicker glass) can handle up to 4.5 volumes. PET bottles are safer as they deform rather than shatter, handling about 3.5 volumes.

What should I do if I suspect bottle bombs?

If you think your bottles are overcarbonated: place them in a sealed container or cool them to near-freezing (cold suppresses CO2 production). Carefully open bottles over a sink. If bottles are visibly swollen (PET) or making creaking sounds, consider carefully venting them all immediately.

Can I use this calculator for Belgian-style beers?

Yes — Belgian beers often target higher carbonation (3.0-4.0 volumes). Use thick Belgian-style bottles rated for higher pressures. Never use standard bottles for high-carbonation styles like Saison or Belgian Tripel.

BrewCalcs

Bottle Bomb Calculator

Check if your beer is safe to bottle based on gravity readings and priming sugar.

Original Gravity (OG)

Current Gravity

Your latest hydrometer reading

Expected Final Gravity (FG)

Where you expect gravity to finish

Priming Sugar

Grams of sucrose per litre

Bottle Type

How We Calculate This

CO2 Volume Calculation

Total CO2 in the bottle comes from three sources:

1. Residual CO2 (~0.85 volumes at 20°C) — already dissolved in the beer.

2. Priming Sugar CO2 — approximately 0.5 volumes per g/L of sucrose added.

3. Residual Fermentable Sugar — if gravity has not reached expected FG, each remaining gravity point produces ~0.5 additional CO2 volumes per litre when fermented in the bottle.

Safety Threshold

Standard glass bottles fail at around 3.0 volumes CO2. If total calculated CO2 exceeds this, there is a risk of bottle bombs.

Frequently Asked Questions

Related Calculators

Fermentation Time Calculator

Estimate primary and secondary fermentation duration for your beer.

Diacetyl Rest Calculator

Calculate timing and temperature for a diacetyl rest in lagers.

Cold Crash Calculator

Calculate cold crash timing and temperature for clear beer.

Secondary Fermentation Calculator

Determine if and when to transfer to secondary fermentation.

Lag Time Calculator

Estimate yeast lag time based on pitch rate, temperature and viability.

Last updated: 2025-02-20

All calculations are estimates. Always verify values and adjust based on your equipment and ingredients.