Second fermentation (often called “F2”) is when you bottle finished kombucha with fruit, juice, herbs or spices and seal it for a few more days. The yeast in the kombucha eats the new sugar and makes carbon dioxide, which can’t escape the sealed bottle – so you get flavor and fizz. A good starting point: about 10–20% fruit or juice to 80–90% kombucha, sealed for 2–5 days at room temperature, then refrigerated.
How Second Fermentation Works
First fermentation happens in an open jar under a cloth, so gas escapes and the SCOBY turns sweet tea into tart kombucha. Second fermentation happens in closed bottles: the remaining yeast ferments the sugar in whatever you add, the gas dissolves into the kombucha, and the flavorings infuse it.
What controls the fizz:
- Sugar: sweeter fruit and juice (mango, pineapple, grapes, berries) make more fizz; herbs and cucumber make very little on their own.
- Temperature: warmer is faster. At 72–78°F (22–26°C), 2–3 days is often enough.
- Time: longer means more fizz – and more alcohol.
- The seal: flip-top bottles with good gaskets hold pressure; loose caps don’t.
- A lively first ferment: bottle kombucha that still has a touch of sweetness.
How to Do a Second Fermentation
- Finish the first ferment. The kombucha should be tart with a little sweetness left. Set aside your SCOBY with 1–2 cups of kombucha as starter for the next batch. New to brewing? Start with our kombucha brewing guide.
- Add the flavoring to clean bottles. Roughly 2–4 tablespoons of chopped or mashed fruit, or 2–4 oz (60–120 ml) of juice, per 16 oz (500 ml) bottle. See the table below.
- Fill with kombucha using a funnel, leaving 1–2 inches (2.5–5 cm) of headspace, and seal.
- Leave at room temperature, out of direct sunlight, for 2–5 days.
- Check the pressure. Once a day, open a bottle briefly over the sink (“burping”) – or chill one bottle and open it to test the fizz.
- Refrigerate all the bottles as soon as the fizz and flavor are right. Cold slows the yeast down.
- Strain when serving if you don’t want the fruit pieces.
20 Second Fermentation Flavor Ideas
Amounts are per 16 oz (500 ml) bottle. Times are at about 70–75°F (21–24°C); check sooner if your kitchen is warm.
| Flavor | What to add | Days |
|---|---|---|
| Ginger-lemon | 2 tsp grated ginger + 2 lemon slices | 3–5 |
| Strawberry-basil | 4–5 strawberries, halved + 3–4 basil leaves | 3–4 |
| Blueberry-lavender | 3 tbsp blueberries + ¼ tsp dried culinary lavender | 3–4 |
| Raspberry-lemon | 3 tbsp raspberries + 2 lemon slices | 3–4 |
| Peach-ginger | ¼ cup diced peach + 1 tsp grated ginger | 3–5 |
| Pineapple-coconut | 3 tbsp pineapple + 2 tbsp coconut water | 2–3 |
| Mango-lime | ¼ cup diced mango + 2 lime slices | 3–4 |
| Passion fruit-ginger | pulp of 1 passion fruit + 1 tsp grated ginger | 3–4 |
| Turmeric-orange | 1 tsp grated turmeric + ¼ cup orange juice + pinch of black pepper | 3–4 |
| Mango-cayenne | 3 tbsp mango + a pinch of cayenne | 3–4 |
| Pineapple-jalapeño | 3 tbsp pineapple + 2–3 thin jalapeño slices | 2–3 |
| Triple berry | 1 tbsp each strawberries, blueberries, raspberries | 3–4 |
| Blackberry-sage | 3 tbsp blackberries + 2–3 sage leaves | 3–4 |
| Cherry-vanilla | ¼ cup pitted cherries + 1-inch piece vanilla bean | 4–5 |
| Cucumber-mint | 3–4 cucumber slices + 5–6 mint leaves + 1 tbsp apple juice | 4–5 |
| Hibiscus | 1 tbsp dried hibiscus steeped in ¼ cup hot water, cooled | 3–4 |
| Chamomile-apple | 1 chamomile tea bag steeped in a little water, cooled + ¼ cup apple juice | 3–4 |
| Cranberry-orange | 3 tbsp cranberries + 2 tbsp orange juice + small cinnamon stick | 4–5 |
| Apple-cinnamon | ¼ cup diced apple + small cinnamon stick + 2 cloves | 4–5 |
| Pomegranate | 3 tbsp pomegranate seeds, lightly crushed | 3–4 |
Tips: ginger gets spicier the longer it sits; remove chili and whole spices before refrigerating if you don’t want them stronger; frozen fruit works as well as fresh; low-sugar flavors (herbs, cucumber, tea) need a splash of juice or a teaspoon of sugar to fizz.
Bottles and Safety
- Use bottles made for carbonated drinks – thick glass flip-top (swing-top) bottles. Thin decorative bottles and mason jars with metal lids aren’t designed for pressure.
- Don’t overfill and don’t overdo the sugar, especially with very sweet fruit.
- Refrigerate promptly. Bottles left warm for a week or more can build dangerous pressure: chill them before opening, point them away from people and open slowly over the sink.
- Alcohol. Second fermentation raises the alcohol content. In the US, kombucha that reaches 0.5% alcohol at any point is regulated as an alcoholic beverage (TTB), and when New Zealand researchers tested commercial kombucha, 22% of samples were above that country’s 1.15% limit (Nordstrom et al., 2026). Homemade F2 kombucha can be stronger – keep that in mind for children, pregnancy and anyone avoiding alcohol.
Troubleshooting
- Flat: not enough sugar, too cold, too short, or a poor seal. Add a teaspoon of sugar or more fruit, move somewhere warmer and give it 2–3 more days.
- Gushing or foaming over: too much sugar, too warm or too long. Chill before opening and use less fruit next time.
- Too vinegary: the first ferment went too long – bottle a day or two earlier next time.
- Tastes boozy: the F2 ran too long or too warm; refrigerate sooner.
- Mold: fuzzy growth (white, green, blue or black) means discard. Keep fruit from floating above the liquid for days and use clean bottles.
- A thin new SCOBY in the bottle: normal – strain it out.
How long flavored kombucha keeps: see how long kombucha lasts. Other fizzy ferments: water kefir soda flavors and fermented drinks like kombucha.
