If you've already mastered the art of making kombucha in a glass container, you might be wondering why your kombucha doesn't taste 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 sparkling.
Secondary fermentation is also a great time to add flavors to your kombucha. Fruit is an especially good choice, as is ginger. I love blueberries. This is a place where you will want to experiment to see what tastes good to you. With a few simple rules, the world of flavor will open 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. Instead of drinking it right away, pour it into a bottle with a swing-top cap or apply your own bottlecaps to clean beer bottles, as though you were brewing beer. Leave some air space at the top, but not too much.
Once bottled, you allow the kombucha to remain out at room temperature for 24 to 72 hours or longer, depending on your kombucha and your ambient temperature. I usually pick one bottle to test for fizziness. Be careful because the other bottles will be still fizzier since you will be opening the same one and releasing some of the carbonation. I have had bottles nearly explode after just three days, so test daily and make sure you are careful when opening.
When the fizziness and tartness/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 more tart, even vinegar-y, over time.
You may have a small, thin scoby grow at the top surface of the kombucha in the bottle. If this bothers you, pour the kombucha through a mesh strainer before drinking. (I have actually poured mine through a strainer into glasses, or into a pitcher to serve a larger group.)
I love to chop ginger into matchstick-sized pieces and drop it into each bottle for the secondary fermentation stage. It is my favorite flavor of kombucha. I also like my brew quite tart, so I don't add more sugar to this 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 adds delicious flavors kombucha. You can add fruit juice, either freshly made or purchased in bottles at the store. Fruit juice concentrate will add more flavor and less sweetness. I add 2-3 ounces of juice for each quart of kombucha. Cranberry-citrus-ginger is a delicious winter health combination. Elderberry is also medicinal - antiviral, especially flu - and tasty.
For fruit, blueberries and raspberries have worked out really well for me. I just drop a handful into the bottle one by one. You can filter out fruit and rebottle before refrigerating. Be careful of mushier fruits. I have read negative reports of using bananas and strawberries. You can add both whole fruit and fruit juice. Also, if using frozen fruit, no need to defrost. Just plop the fruit in the bottle and let it defrost naturally.