🫧 Kombucha Second Ferment Carbonation Calculator
Enter your desired carbonation level and room temperature to see a typical second ferment (F2) time range. Burp bottles daily to release pressure safely.
How the day range is built
Each fizz level starts from a base number of days, temperature shifts it, and the page reports that day plus two:
base: light 1, medium 3, strong 5
if temp ≥ 80°F: base - 1 (never below 1)
if temp < 68°F: base + 1
shown = base to base + 2 days| Fizz | Under 68 °F | 68-79 °F | 80 °F and up |
|---|---|---|---|
| Light | 2-4 days | 1-3 days | 1-3 days |
| Medium | 4-6 days | 3-5 days | 2-4 days |
| Strong | 6-8 days | 5-7 days | 4-6 days |
The defaults, medium fizz at 75 °F, give 3-5 days. Light fizz cannot go below one day, so the warm column repeats the middle one, and temperature enters only at those two thresholds.
What actually makes the bubbles
F2 is yeast eating sugar in a sealed bottle, and the CO2 has nowhere to go. The tool never asks what you added: 10-20% fruit juice by volume, or 1-2 teaspoons of sugar per 16 oz bottle, is the dose behind these times, and doubling it gives much more pressure in the same days.
- Use bottles built for pressure: swing-top or champagne glass, never screw-top juice bottles or thin decorative glass.
- Leave 1 to 1.5 inches of headspace; a brim-full bottle fizzes over on opening.
- Fill one plastic bottle as a gauge. When it is rock hard, the glass beside it is too.
Frequently asked questions
How long does kombucha F2 take for medium fizz?
3 to 5 days at 75 °F. A cold room adds a day at each end; 80 °F or warmer gives 2 to 4.
Do I have to burp the bottles?
Yes, once a day. It is the only way to tell how far a sealed bottle has got, and it vents pressure that otherwise keeps climbing.
Why did my second ferment come out flat?
Usually no sugar left, too little headspace, a lid that is not gas-tight, or a cold room. Add juice, seal properly, and allow the longer end of the range.