The bottle does the last step: fill, add sugar, seal. The yeast still alive eats the sugar inside the sealed volume, making CO₂ that the liquid can't shed, carbonation, at the exact strength you chose. It's the same fermentation you already ran, now in a pressure vessel.
The liquid remembers how warm it was after fermentation finished: the warmer it sat, the less CO₂ it kept. The app reads a real table (Hibberd's, interpolated between its points): at 0 °C the liquid holds 1.7 volumes; at 12, 1.12; at 22, 0.83; at its top, 0.78. Your number is the warmest temperature the batch reached after the ferment ran out, not today's room.
Per liter of finished batch: (target volumes − dissolved) × 4.0 g of table sugar, the one constant that turns volumes into grams, scaled by your sugar's factor, times the liters. Worked (the calculator's shape): 20 L of cider that sat warm at 20 °C (0.88 dissolved), carbonated to 2.5 volumes table sugar: (2.5 − 0.88) × 4.0 = 6.48 g/L → 129.6 g of sugar for the batch.
| sugar | the factor |
|---|---|
| Table sugar (sucrose) | 1.0, the reference |
| Corn sugar (dextrose) | 1.15, 15% more by weight for the same carbonation (Hibberd's figure) |
Both ferment clean in this range; pick by what you own. The app carries both as its calculator's own choices.
The recipes shelf's sparkling cider recipe opens exactly here: 4 L of hard cider fermented completely dry (log it: the same hydrometer reading a few days apart), warmest since fermentation 20 °C, target 2.5 volumes. The calculator: (2.5 − 0.88) × 4.0 = 6.48 g/L → 26 g of table sugar for the 4 L batch, comfortably inside Jolicoeur's 6–15 g/L pétillant-to-sparkling band. Jolicoeur's own method: dissolve the sugar in a little boiled water, stir it gently into the cider, bottle, keep the bottles at room temperature, and it sparkles within a few weeks.
| reading | says |
|---|---|
| target above 3 volumes | above the 2–3 volumes standard beer bottles hold, bottles made for the pressure, or aim lower (Brewer's Friend's priming figures) |
| cider: above 15 g/L | above Jolicoeur's 6–15 g/L range from pétillant to fully sparkling, the caution fires when your per-liter sugar leaves that band |
The same math covers cider, mead, beer and kombucha's second ferment, one constant, one warm-temp read, the sugar's factor. The app's calculator runs it and carries these same checks.
| You did | What it costs | The fix |
|---|---|---|
| Entered today's cellar temp, not the warmest the batch reached since fermenting finished | A wrong dissolved-CO₂ read, so over- or under-dosed bottles | The number the app wants is the warmest temperature after the ferment ran out, that's the memory that matters |
| Measured dextrose as if it were table sugar | About 15% under-carbonated | Hibberd's factor: corn sugar needs 1.15× the weight for the same carbonation |
| Aimed above 3 volumes | Above the 2–3 volumes standard beer bottles hold | Bottles made for the pressure, or aim lower (the caution the app carries) |
| Cider sugar above 15 g/L | Out of Jolicoeur's 6–15 g/L range | The caution fires; bring the per-liter number back inside the band |
| the mistake | what it costs |
|---|---|
| today's room temperature instead of the warmest the batch sat | the liquid's memory is the warmest point after the ferment; a cooler reading means double-dissolved CO₂ and overcarbonated bottles |
| a "5 oz per 5 gallons" rule from a forum | it hides the volumes and the temperature both; the real math is four numbers, not a slogan |
| the sugar type unaccounted | the 4.0 g constant is table sugar; other sugars scale by their factor and the calculator carries it |
| priming the whole batch when the plan said bottles | kegs and bottles take different targets; the calculator asks which, answer it |
The priming calculator reads Hibberd's table interpolated between its points, asks the warmest temperature the batch actually reached, and prints the grams with the sugar's factor applied. The bottling card carries the constant for the shelf.