How priming sugar carbonates your bottles
When you bottle a finished beer, cider or mead, a small dose of sugar gives the remaining yeast one last meal. The CO2 it makes is trapped in the sealed bottle and dissolves into the drink. Too little sugar gives flat bottles, and too much risks gushers or bottles bursting.
The calculator works in three steps:
- Estimate the CO2 already dissolved. Fermentation leaves some CO2 behind, and how much depends on temperature:
CO2 = 3.0378 − 0.050062·T + 0.00026555·T² (T in °F). At 68°F that's about 0.86 volumes.
- Subtract it from your target to find the volumes still needed.
- Convert to sugar. One volume of CO2 is about 1.96 g per liter, and fermentation chemistry tells us how much of each sugar makes that much gas: about 3.8 g/L of table sugar, 4.4 g/L of corn sugar (dextrose monohydrate) or 5.0 g/L of honey per volume.
Carbonation levels by style
| Style |
Volumes of CO2 |
| British ales, stouts |
1.5–2.0 |
| American ales, lagers |
2.2–2.7 |
| Belgian ales, wheat beers |
3.0–4.0 |
| Sparkling cider or mead |
2.5–3.0 |
| Petillant (lightly sparkling) wine or mead |
1.0–2.0 |
Tips
- Dissolve the sugar in a little boiling water, cool it, and stir it gently into the whole batch so every bottle gets the same amount.
- Make sure fermentation is truly finished, with a stable gravity for several days, before bottling. Leftover sugar on top of priming sugar is how bottles explode.
- High-alcohol meads and wines may need fresh yeast at bottling to carbonate reliably.
- Bottles take about 2 to 3 weeks at room temperature to carbonate.
If your cider or mead needs sweetening as well as sparkle, see the back-sweetening calculator. Note that sweetened bottles will keep fermenting unless you pasteurize them.
Method and sources
- CO2 already in the drink: 3.0378 − 0.050062 × T + 0.00026555 × T², where T is the highest temperature (°F) the drink reached after fermentation. It matches the residual CO2 figures Brewer's Friend publishes, such as 0.86 volumes at 68 °F.
- Sugar per volume of CO2: one volume of CO2 is about 1.96 g per liter. Fermentation turns 342 g of sucrose into 176 g of CO2, so table sugar needs 3.82 g per liter per volume. Corn sugar needs 4.41 g, because it is dextrose monohydrate. Honey needs about 5.02 g, assuming it is 80% fermentable sugar. These constants come from the chemistry, not a lookup table.
- Limits: honey varies, and wild yeast or leftover sugar adds CO2 the calculator can't see. Only prime a drink that has finished fermenting, with a stable gravity over several days.
Sources
Frequently asked questions
How much priming sugar for 5 gallons of beer?
For a typical 2.5 volumes of CO2 after fermenting at 68°F, about 4.8 oz (137 g) of corn sugar or 4.2 oz (119 g) of table sugar.
Why does fermentation temperature matter?
Beer holds some CO2 from fermentation, and cooler beer holds more. Use the warmest temperature the beer reached after fermentation, because CO2 that escaped while warm doesn't come back.
How many volumes of CO2 should I aim for?
British ales 1.5 to 2.0, most American ales and lagers 2.2 to 2.7, wheat beers and Belgian ales 3.0 or more, and sparkling cider or mead 2.5 to 3.0. Use bottles rated for high pressure above 3.0 volumes.