Kombucha Second Fermentation: How to Flavor & Carbonate

Kombucha second fermentation (2F) is the optional bottling stage that adds flavor and natural fizz to finished kombucha. Add a measured amount of juice, fruit, or sugar, seal in bottles made for carbonated drinks, and ferment for about 2–3 days, checking daily. Then refrigerate thoroughly before opening. Your ingredients, room temperature, and kombucha all affect how quickly carbonation builds.

This is where you get to make your brew your own. Keep it simple with plain, fizzy kombucha, try a favorite fruit combination, or split a batch into a few different flavors.

Jump to the second-fermentation steps · Juice and sugar amounts · Common questions

Why do a second fermentation?

Two good reasons: flavor and carbonation. Second fermentation gives you a chance to add fruit, juice, herbs, or spices after setting aside your starter for the next batch. You can experiment with the bottles while keeping your brewing culture and starter liquid plain.

The yeast still living in your kombucha consumes fermentable sugar and produces carbon dioxide. A sealed bottle holds that gas, allowing it to carbonate the drink naturally. You do not need a carbonation machine.

Second fermentation is optional. If you enjoy your kombucha straight from first fermentation, you can refrigerate it and drink it that way.

First fermentation, second fermentation, and chilling

• First fermentation (1F): Sweetened tea ferments with your culture and starter liquid in a jar with a breathable cover. This makes the kombucha base.
• Second fermentation (2F): Finished kombucha goes into sealed bottles, usually with a measured flavoring or sugar addition. This is the stage for building natural carbonation.
• Chilling: Refrigeration slows fermentation and helps the drink hold its carbonation. Chill after 2F and keep finished bottles refrigerated.

Already bottled your batch but struggling with fizz? Our kombucha carbonation troubleshooting guide walks through the likely causes and fixes.

What you need for second fermentation

Start with a completed first fermentation. If you have not made your base yet, follow our home kombucha brewing guide first.

• Finished, unflavored kombucha from a successful first fermentation
• Clean bottles intended for carbonated beverages, with sound closures and seals
• Your chosen juice, fruit recipe, sugar, or flavoring pack
• A clean funnel, measuring spoons, and measuring cup
• Refrigerator space for the finished bottles

An airtight lid alone does not make a bottle suitable for fermentation pressure. Skip decorative bottles and chipped or cracked glass. See our second-fermentation bottle guide for selection details, or shop our 16 oz flip-top kombucha bottles.

How to do kombucha second fermentation

1. Save your starter before adding flavors

With clean hands and utensils, set aside your SCOBY and the amount of plain starter liquid required by your brewing recipe. Keep these for your next batch. Do this before adding fruit, juice, or other flavorings.

You do not need to put a piece of the solid SCOBY into each bottle. The liquid already contains living yeast and bacteria that continue fermenting.

2. Measure your flavoring or sugar

Wash your hands, use clean utensils, and rinse fresh fruit under running water before preparing it. Use sound ingredients; fermentation does not rescue spoiled fruit.

For a 16 oz bottle, these are our usual starting options:

• Fruit juice: About ¼ cup juice, then enough kombucha to fill the bottle while leaving headspace. Start with a simple juice rather than a concentrate.
• Plain kombucha: 1 teaspoon cane sugar, then kombucha. Dissolve the sugar in a little kombucha first so it distributes evenly.
• Fruit, herbs, or spices: Follow a measured recipe. Fruit sweetness and ingredient amounts vary, so there is no single amount that works for every combination.
• Bucha Brewers flavoring packs: Follow the included recipe. Each flavor recipe is portioned for six 16 oz bottles and includes all the flavoring ingredients you need.

Choose one approach; do not automatically add the teaspoon of sugar on top of a juice or fruit recipe. Your kombucha also contains residual sugar from first fermentation. These are starting amounts, not a guarantee of a particular carbonation level.

For inspiration, explore our kombucha flavor ideas. If you would rather have the ingredients and recipe ready to go, our second-fermentation flavoring packs make that part easy.

3. Gently stir, fill, and seal

Gently stir the remaining plain kombucha before dividing it among the bottles. This helps distribute the yeast that may have settled near the bottom of your brewing jar.

Add your measured ingredients and kombucha, leaving about 1 inch of headspace, or the space specified by your bottle manufacturer. Do not fill to the brim. Wipe the openings clean, check that the seals sit properly, and close the bottles securely.

Label each bottle with its flavor and bottling date. A quick note about your amounts makes a good batch much easier to repeat.

4. Ferment for about 2–3 days and check daily

Our usual starting window is 2–3 days in a dark space at room temperature. Kombucha cultures generally ferment well around 70–80°F (21–27°C). Cooler rooms can slow things down; warmer conditions can build pressure faster. Do not put sealed bottles on a heat mat or use direct heat to speed up carbonation.

Check your bottles daily, beginning after the first day. Our method includes burping excess carbonation as needed: briefly and carefully opening the closure to release excess gas, then resealing. Keep the bottle upright and pointed away from faces. If pressure seems high, refrigerate thoroughly before attempting to open it.

Burping is not a guarantee against bottle breakage. Pressure can rebuild between checks, and releasing gas repeatedly also releases the fizz you are trying to keep. Suitable bottles, measured additions, monitoring, and timely refrigeration all matter. Do not leave bottles fermenting unattended for an extended period.

Treat 2–3 days as a starting window, not a deadline to force every batch to reach. If a batch is carbonating quickly, refrigerate sooner.

5. Chill thoroughly, then open slowly

Move the bottles to the refrigerator when they are ready. Let them chill all the way through—overnight is a practical routine—before opening to serve.

Open cold bottles slowly over a sink, upright and away from faces. Do not shake them. You can strain fruit pieces into your glass after opening if you prefer a smoother drink.

Keep finished kombucha refrigerated. Cold slows fermentation; it does not make a live brew shelf-stable or remove pressure that has already built up.

How do you know when second fermentation is done?

The goal is a flavor and carbonation level you enjoy. Time alone cannot tell you exactly how much pressure is inside a bottle, and a few visible bubbles are not a reliable pressure measurement.

For your first batch with a recipe, chill a bottle within the usual 2–3-day window and assess it cold. Keep notes on the ingredients, room temperature, and timing. Use what you learn to adjust the next batch in small steps instead of adding more sugar and more time all at once.

If your kombucha is still flat—or gushes when opened—use our carbonation guide to check the seal, sugar source, temperature, yeast distribution, and chilling.

Kombucha second-fermentation FAQs

Can I skip second fermentation?

Yes. Second fermentation is optional. Refrigerate finished first-fermentation kombucha and enjoy it plain if you like its flavor. Bottling for 2F is useful when you want to develop natural fizz or experiment with flavors.

Can I do second fermentation without fruit?

Yes. For plain kombucha, our starting method uses 1 teaspoon cane sugar per 16 oz bottle. Fruit is not required. If your base is already very sweet, remember that it already supplies fermentable sugar; adding more is not always the answer.

Do I need a SCOBY in each bottle?

No solid SCOBY is needed in the bottle. Living yeast and bacteria remain in the kombucha liquid. Set aside your SCOBY and plain starter for the next batch before flavoring.

Can second fermentation happen in the refrigerator?

Fermentation slows considerably in the refrigerator, so it is not our usual method for building carbonation. We use a short, monitored room-temperature 2F, then refrigerate. Keep finished bottles cold.

Does second fermentation remove all the sugar?

No. Yeast consumes some sugar, but the amount left varies with the base kombucha, added ingredients, culture, and timing. A finished batch is not automatically sugar-free, and taste alone cannot tell you its sugar content.

Does second fermentation increase alcohol?

It can. Yeast produces alcohol as well as carbon dioxide, and alcohol can increase during sealed fermentation. Home-brewed kombucha is not reliably alcohol-free; you cannot determine its alcohol content from taste or the number of days it fermented.

Make your next batch your own

Start with one measured recipe, keep a few notes, and build from there. Once you find a combination you love, bottling day gets even better.

As a family-run Colorado business, we have helped thousands of customers brew at home since 2018. Explore our second-fermentation recipes and guides, or pick a flavoring pack for your next batch.