If you've already mastered the art of making kombucha in a glass container, you might be wondering why your kombucha isn't fizzy and sparkling like the kind you buy at the store. That's because you need to secondary ferment kombucha in a sealed bottle, or force carbonate it with bottled carbon dioxide, to make it bubbly.
Secondary fermentation is also a great time to add flavors to your kombuchas, such as blueberries or ginger. Feel free to experiment, as long as you follow a few simple rules, to see what tastes good to you.
How to Secondary Ferment Kombucha
The basic idea with secondary fermentation is to draw off the kombucha liquid that has been brewing with your scoby (the kombucha culture). Instead of drinking it right away, pour it into a bottle with a swing-top cap or apply your own bottle caps to clean beer bottles (as though you were brewing beer). Leave some air space at the top, but not too much.
Once bottled, allow the kombucha to remain at room temperature for 24 to 72 hours, or longer, depending on your kombucha and your ambient temperature. Test one bottle for fizziness. When the fizziness, tartness, and taste are to your liking, simply refrigerate your brew. Be aware that refrigeration will slow fermentation, but it will still occur—so if you drink your kombucha over months instead of days or weeks, be sure to release the pressure and excess carbonation every few weeks, and realize that it will continue to consume sugar and grow tarter, even vinegary, over time.
You may have a small, thin scoby grow on the top surface of the kombucha in the bottle. If this bothers you, pour the kombucha through a mesh strainer before drinking.
This stage of fermentation is a perfect opportunity to bring another flavor to the drink, and ginger complements the kombucha very nicely. Chop fresh ginger into matchstick-sized pieces and drop some into each bottle for the secondary fermentation stage. You could also brew chopped ginger and water into a "ginger juice" that you add to the bottle with some fruit juice or a little sugar. Lemon juice makes a nice addition for a lemon-ginger flavor.
Fruit also adds delicious flavors to kombucha. You can add fruit juice, either freshly made or purchased in bottles at the store, or fruit juice concentrate, which will add more flavor and less sweetness. Add 2 to 3 ounces of juice for each quart of kombucha. Cranberry-citrus-ginger is a delicious combination promoting winter health, and elderberry is also medicinal and tasty.
When it comes to fresh fruit, blueberries and raspberries work well; just drop a handful into the bottle one by one. (You can filter out the fruit and rebottle before refrigerating.) Be careful of mushier fruits like bananas and strawberries. Also, if you use frozen fruit, no need to defrost beforehand—just plop the fruit in the bottle and let it defrost naturally. You can also add both whole fruit along with fruit juice if desired.