Kombucha Second Fermentation
Kombucha Second Fermentation: How to Get the Fizz Right Every Time
The Short Answer
Kombucha second fermentation is where you build the fizz. Once your first ferment is complete and the SCOBY is removed, bottle the liquid with a small amount of fruit, juice or ginger, seal tightly and leave at room temperature for 2 to 3 days. The remaining yeast consumes the added sugar and produces CO2 that has nowhere to escape in a sealed bottle, creating natural carbonation. Move to the fridge once carbonated to your liking.
Getting the fizz right every time comes down to three things: the right bottles, the right amount of flavouring and the right temperature for your Irish kitchen. This guide covers each one so you can go from a flat first ferment to a consistently sparkling bottle with confidence.
What You Need for a Kombucha Second Fermentation
Second fermentation requires just three things: your finished first ferment kombucha with the SCOBY removed, swing top glass bottles designed to handle pressure, and a small amount of sugar in the form of fruit, juice or plain sugar to feed the remaining yeast. The carbonation builds because the bottles are sealed, trapping the CO2 the yeast produces as it consumes the added sugar. The more sugar you add, the faster and stronger the carbonation. Getting the balance right is what this guide is about.
Before you bottle, decide which approach suits you. Here is a plain guide to both options.
Option 1: Plain Carbonation, No Added Flavour
What to do: Pour your finished kombucha into swing top bottles, add half a teaspoon of plain cane sugar per 500ml bottle, seal and leave at room temperature for 2 to 3 days.
What you get: Clean, light carbonation that lets the natural flavour of your kombucha come through without any added fruit flavour. Good for your first second ferment when you want to understand the process before experimenting.
Best for: Beginners, purists, and anyone who wants to taste the kombucha itself rather than the flavouring.
Option 2: Fruit or Juice Infusion
What to do: Add around 100ml of fruit juice, a small handful of fresh fruit or a thumb of freshly grated ginger to each 500ml bottle before sealing. Fill the remaining space with finished kombucha, leaving 2 to 3cm headspace at the top, then seal and leave at room temperature for 2 to 3 days.
What you get: Strong carbonation and a distinct fruit or ginger flavour. The natural sugars in the fruit feed the yeast more aggressively than plain sugar, producing a livelier fizz and a more complex flavour profile.
Best for: Anyone who wants a flavoured sparkling drink. Browse our kombucha recipes for flavour combination ideas that work particularly well with Irish kombucha.
NutriBrew Tip: Always leave 2 to 3cm of headspace at the top of each bottle. Without this gap the pressure has nowhere to build safely and bottles can crack or overflow when opened. Burp each bottle once daily by opening it briefly over a sink to check pressure levels, particularly in warmer kitchens above 22°C.
Kombucha Second Fermentation Flavour Guide
The fruit or ingredient you add to your bottles is what makes each batch your own. Different additions produce different levels of carbonation, different flavour profiles and different sweetness levels in the finished drink. Here is a practical guide to the most popular options and what to expect from each.Fresh Ginger
Amount: 1 thumb, grated per 500ml
Flavour: Spicy, warming, clean
Carbonation: Very high, best for experienced brewers
Raspberry
Amount: Small handful fresh or frozen per 500ml
Flavour: Tart, fruity, vibrant
Carbonation: High, great for beginners
Mango Juice
Amount: 100ml per 500ml bottle
Flavour: Sweet, tropical, smooth
Carbonation: High, reliable and consistent
Apple Juice
Amount: 100ml per 500ml bottle
Flavour: Mild, sweet, familiar
Carbonation: Medium, ideal for first time second ferments
NutriBrew Tip: Ginger produces the strongest carbonation of any common addition, so if it is your first second ferment start with apple juice or blueberries for a more predictable result. Once you are comfortable with how your bottles behave, ginger is worth trying for a seriously fizzy brew. For step by step recipes with exact quantities visit our kombucha recipes page.
How Long Does Kombucha Second Fermentation Take?
Temperature is the biggest variable in second fermentation timing, and in an Irish kitchen that can mean a significant difference between a summer batch and a winter one. Here is what to expect at each temperature range and what to do to get consistent results year round.
Second Fermentation Timing Guide
20 to 24°C, typical Irish summer kitchen: Carbonation builds in 2 to 3 days. Check bottles from day 2 onwards and move to the fridge once your preferred fizz level is reached.
18 to 20°C, typical Irish spring or autumn kitchen: Allow 3 to 5 days. The yeast is still active but working more slowly. Burp bottles daily and be patient.
Below 18°C, typical Irish winter kitchen: Carbonation can take 5 to 10 days or more. Move your bottles to a warmer spot such as an airing cupboard, on top of a fridge or near a boiler. A consistent temperature above 18°C makes a significant difference.
Once the fizz is right: Move bottles to the fridge immediately. Cold temperatures stop the yeast from producing more CO2 and lock the carbonation in at exactly the level you want.
NutriBrew Tip: Kombucha stored in the fridge continues to develop slowly even at cold temperatures. A bottle you open after two weeks will often taste noticeably better than one you tried on day one. If you can hold off, it is worth the wait. Finished kombucha keeps well in the fridge for up to 3 to 4 weeks.
Common Questions About Kombucha Second Fermentation
Second fermentation is where most new brewers have questions. Here are the ones we hear most often from people doing their first F2, answered clearly so you can bottle with confidence. For a full library of troubleshooting and SCOBY care questions visit our Kombucha FAQ and Troubleshooting Guide.
My bottles have been sealed for 3 days but there is no fizz. What went wrong?
The most likely cause is temperature. If your kitchen is below 18°C the yeast in the kombucha will be too sluggish to produce enough CO2 for noticeable carbonation in 3 days. Move the bottles to a warmer spot, an airing cupboard or on top of a fridge works well, and leave them for another 2 to 3 days. Also check that you added enough sugar or fruit to give the yeast something to work with. Plain kombucha with no added sugar will carbonate very slowly if at all.
I opened a bottle and it exploded everywhere. How do I prevent this?
This happens when bottles are left at room temperature for too long or the kitchen is warmer than expected. The yeast keeps producing CO2 and the pressure builds beyond what you want. To prevent it, burp your bottles once daily by opening them slightly over a sink to release excess pressure, and move them to the fridge as soon as you hear a healthy hiss when opening. Always open bottles slowly and point them away from you. In warm weather above 22°C, check bottles from day 2 rather than waiting for day 3.
Do I need to remove all the SCOBY before bottling?
Yes, the SCOBY and any large yeast strands should be removed before you bottle for second fermentation. The SCOBY belongs in your next batch of sweet tea, not in a sealed bottle. Small brown stringy bits are fine to leave in, these are yeast clusters rather than SCOBY material and will not cause any problems. If you prefer a cleaner pour, strain the kombucha through a fine mesh strainer before bottling.
Can I do a second fermentation without swing top bottles?
Not safely. Regular screw top jars, repurposed glass bottles and plastic containers are not designed to handle the pressure that builds during second fermentation. Swing top bottles with rubber gaskets are the only reliable option for home brewing. They are built to contain pressure and the gasket will vent slightly if pressure becomes excessive rather than the glass cracking. The investment in a set of good swing top bottles is worth it from the very first batch.
My second ferment kombucha tastes more sour than my first ferment. Why?
This is normal and happens for two reasons. First, fermentation continues inside the sealed bottle during F2 and the bacteria keep producing organic acids, making the drink progressively more tart over time. Second, if your first ferment was already quite sour before bottling, the second ferment will amplify that. To get a less sour result, bottle your kombucha a little earlier in the first fermentation cycle, around day 7 rather than day 10 to 14, so it still has some residual sweetness when it goes into the bottles.