You've brewed your first batch of kombucha. It tastes great — tangy, slightly sweet, and full of that distinctive fermented character. But it's a little flat.
That's where second fermentation comes in.
Second fermentation (often called 2F) is the step that transforms your kombucha from a still, jar-fermented tea into a naturally fizzy, bottled drink. It's also where you add flavour — and the results can be genuinely spectacular.
Here's everything you need to know.
What Is Second Fermentation?
First fermentation happens in your brewing jar, where your SCOBY converts sweetened tea into kombucha over several days.
Second fermentation happens after you've removed your SCOBY and bottled your kombucha. You seal it in airtight bottles with a small amount of added sugar (usually from fruit, juice, or honey), and the naturally occurring yeast in the kombucha continues to ferment — producing carbon dioxide that has nowhere to go.
The result? Bubbles.
What You'll Need
- Freshly brewed kombucha (from your first fermentation)
- Airtight swing-top or screw-top glass bottles
- Your chosen flavouring — fruit, juice, ginger, herbs, or spices
- A funnel (optional, but helpful)
- A fine strainer (optional)
The quality of your bottles matters. Airtight glass bottles designed for fermentation are best — they can handle the pressure build-up. Standard glass jars or loosely sealed bottles won't trap the CO₂ you need for carbonation.
Step-by-Step: How to Do a Second Fermentation
1. Brew and taste your first fermentation
Before bottling, your kombucha should be ready — tart, flavourful, and no longer overly sweet. Taste it. If it still tastes like sweet tea, give it more time.
2. Remove your SCOBY
Carefully remove your SCOBY and set it aside in a clean container with some starter tea from the batch. This is what you'll use to start your next brew.
3. Add your flavouring to each bottle
This is the fun part. Add your chosen flavouring directly to each bottle before pouring in the kombucha. A little goes a long way — you're primarily feeding the yeast, not making a smoothie.
Good starting ratios per 500ml bottle:
- Fresh or frozen fruit: 1–2 tablespoons
- Fresh ginger (grated): ½–1 teaspoon
- Fruit juice: 2–3 tablespoons
- Honey or sugar (if not using fruit): ½–1 teaspoon
4. Fill the bottles
Pour your kombucha into each bottle, leaving about 2–3cm of headspace at the top. Less headspace = more pressure = more fizz, but too little headspace can cause over-pressurisation.
Seal the bottles tightly.
5. Ferment at room temperature
Leave your sealed bottles at room temperature for 2–4 days. The warmer your environment, the faster carbonation builds.
6. Burp the bottles daily
Once a day, carefully open each bottle slightly to release a little pressure, then reseal. This is called "burping" — it prevents bottles from over-pressurising and helps you gauge how carbonation is developing.
If you hear a satisfying hiss when you open the bottle, carbonation is building nicely.
7. Taste and refrigerate
After 2–4 days, open a bottle and taste it. If the fizz is where you want it, move all bottles to the fridge. Cold temperatures slow fermentation and lock in your carbonation.
Refrigerated second-fermentation kombucha will keep well for several weeks.
Flavour Ideas to Try
Once you've got the basics down, experimenting with flavours is one of the most enjoyable parts of home brewing. Some tried-and-tested combinations:
- Ginger + lemon — classic and refreshing
- Raspberry + rose — floral and fruity
- Passionfruit — works beautifully with the tartness of kombucha
- Blueberry + lavender — subtle and sophisticated
- Apple + cinnamon — perfect for cooler months
- Mango + chilli — unexpected and delicious
- Pineapple + mint — bright and tropical
- Orange + turmeric — earthy and vibrant
Frozen fruit works particularly well because the cell walls are already broken down, making it easier for the yeast to access the natural sugars.
Why Isn't My Kombucha Fizzy?
If you're not getting the carbonation you hoped for, a few things could be at play:
Not enough sugar. Carbonation comes from yeast consuming sugar and producing CO₂. If there's not enough sugar in your flavouring, there's less fuel for the process. Try adding a small amount of fruit juice or a pinch of sugar alongside your flavouring.
Bottles aren't airtight. If CO₂ is escaping, it can't build up. Check your seals — swing-top bottles are ideal for second fermentation.
Too cold. Fermentation slows significantly in cool environments. If your home is cold, try finding a warmer spot for your bottles during 2F.
Not enough yeast. If your first fermentation kombucha is very clear and low in natural yeast, carbonation can be slow. A slightly yeasty, cloudier kombucha tends to carbonate more vigorously.
Too short a ferment time. Give it a little more time. Some batches take 3–4 days to develop good fizz, especially in cooler weather.
A Note on Safety: Watch Your Pressure
Second fermentation involves building pressure inside sealed bottles. Always use bottles rated for carbonated beverages, burp your bottles daily, and refrigerate promptly once carbonation has reached your preferred level.
If a bottle feels very hard when you squeeze it (for plastic) or you hear significant pressure on opening, it may be over-carbonated. Open carefully over a sink or outside, and consider refrigerating earlier next time.
Ready to Start Brewing?
Second fermentation is one of those steps that makes home brewing genuinely rewarding. The first time you open a bottle and hear that satisfying fizz — knowing you made it yourself — is hard to beat.
If you haven't started your kombucha journey yet, our Organic Kombucha SCOBY comes with starter tea and brewing instructions to get your first batch underway.
Already brewing? Explore our full fermentation range — including water kefir grains, jun kombucha kits, and fermentation accessories to help you build out your home setup.
Disclaimer: Kombucha is a fermented beverage intended to be enjoyed as part of a varied, balanced diet. The fermentation process involves live cultures and natural carbonation — always use appropriate equipment and follow safe food handling practices.