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How much sugar to carbonate this?

Priming sugar for a target carbonation, accounting for the CO₂ the cider already holds — and the pressure the result will reach, which is the half of the answer most calculators leave out.

Priming sugar

Not the temperature now — the temperature it has equilibrated at. Colder cider already holds more dissolved gas.

A light prickle rather than a fizz. Typical of French bottled cider and many bottle-conditioned ciders.

Priming sugar

52.0 g

Per litre: 2.60 g/L

This is an estimate from a model, not a measurement.

How this is worked out
  1. Already dissolved: at 12.0 °C, about 1.12 volumes of CO₂
  2. Still needed: 1.80 − 1.12 = 0.68 volumes
  3. As CO₂: 0.68 × 1.96 = 1.34 g/L
  4. As sugar: 1.34 ÷ 0.5143 = 2.60 g/L
  5. Total: 2.60 g/L × 20.0 L = 52.0 g
  6. Resulting pressure, cellar: roughly 1.1 bar at 20 °C
  7. Resulting pressure, warm store: roughly 1.7 bar at 30 °C — this is the figure the glass has to survive
What this assumes (6)
  • This assumes fermentation has genuinely finished. It is the assumption that breaks bottles: priming a cider that still has sugar to ferment adds this pressure on top of whatever the remaining sugar produces, and the result can be far outside what the glass will hold. Confirm a stable gravity over several days before priming anything.
  • Use bottles rated for pressure. Standard still-wine bottles are not, and a crown-capped beer bottle is safe to roughly 4 bar while a Champagne bottle is rated far higher.
  • Condition somewhere the failure of a bottle would not injure anyone — not a kitchen worktop, not a warm airing cupboard — and check one bottle before assuming the batch is where you wanted it.
  • The residual CO₂ estimate assumes the cider has been sitting at the stated temperature long enough to equilibrate. A cider just moved from a cold store still holds the gas the cold store gave it.
  • The temperature you entered is the one the cider is at now, and it sets how much sugar to add. The pressure the bottles must survive is set by the warmest they will ever get, which is why both figures are shown: at 30 °C this carbonation reaches about 1.7 bar against 1.1 bar in a cellar.
  • Pressure prediction here is indicative rather than exact. It assumes the cider has equilibrated at the temperature you gave, that fermentation is genuinely finished, and that the sugar is fully consumed — and it says nothing about the condition of the individual bottle, which is what actually fails. Treat the number as the order of magnitude of the risk, not as a specification.

The part that matters

Priming calculators normally stop at the sugar figure, which is the half of the answer that cannot hurt anyone. The other half is the pressure that results, and this tool gives it.

Bottles fail for one reason far more often than any other: the cider had not actually finished fermenting. Priming sugar then adds its pressure on top of whatever the remaining sugar produces, and the total can be several times what the glass will hold. A gravity reading that has not moved over three or four days is the minimum evidence before priming anything.

Perry deserves particular caution here. Sorbitol keeps a perry’s gravity higher than a cider’s at the same stage of fermentation, so a perry can look finished on the hydrometer while sugar remains — and the gravity-derived alcohol figure understates how much fermentation is still available.

Handling a batch you are unsure about

Chill it first, which lowers the pressure. Do not shake or invert it. Move it in a closed crate rather than by the neck. If a bottle needs venting, do it behind something, with eye protection, pointed away from you. Never condition bottles in a warm room, an airing cupboard or a car, and never in a freezer.

Related tools

Where this reading comes from

Guides that reach this calculator, and what the number decides once you have it.