How the second ferment calculator works
After the first ferment, kombucha goes into sealed bottles with a little fruit, juice, or puree. The leftover sugar plus the flavoring feeds the culture again, building natural carbonation and taste. This tool scales the flavoring to your batch volume and intensity, splits it across 16 ounce bottles, and reminds you of the typical 3 to 7 day window so you get fizz without guesswork.
How much fruit or juice to add
A good starting point is roughly 10 to 15 percent juice by volume, or about 60 to 150 grams of fresh fruit or puree per liter, adjusted for how bold you want it. Light gives a subtle flavor and gentle fizz, while strong gives a fruit forward, lively bottle. Juice carbonates fastest because its sugars are readily available, so start on the lower end if you are new to it.
Getting good carbonation safely
Use bottles built for pressure, such as flip top or thick glass, and leave about an inch of headspace. Seal them and leave at room temperature, around 70 degrees, for a few days. Warmth and more sugar mean faster, stronger fizz. The catch is that bottles can over pressurize, so burp one daily to check, and refrigerate as soon as the carbonation is where you like it to slow it down.
Flavor ideas
Ginger and lemon, mixed berry, mango, pineapple, apple cinnamon, and pomegranate are all reliable. Fresh fruit and juice carbonate well; dried fruit and extra sugar carbonate hard and fast, so use them sparingly. Strain out solids when you pour, or use a wide mouth bottle. Keep notes on what you added so you can repeat the batches you love.
Frequently asked questions
How much juice for second fermentation? About 10 to 15 percent of the bottle volume, so roughly two to three tablespoons in a 16 ounce bottle.
How long does second fermentation take? Usually 3 to 7 days at room temperature, faster when warm or with more sugar.
Why are my bottles not fizzy? Often too little sugar or flavoring, too cold, or loose seals; add a touch more juice and keep them warmer.
Related calculators: Kombucha, Fermentation Sugar, Drink Batch.