Add apple or apple juice to bottle and tightly seal lid.
Leave bottle on counter to build carbonation. This could take anywhere from 2 to 14 days, depending on temperature. “Burp” kombucha daily to release some pressure by opening lid slightly and then tightening it again.
When kombucha is as fizzy and sour as you like (this could range from a small fritz to a ferocious fizz), store it in fridge to slow fermentation process. Enjoy cold. Keeps for 3 months.
Notes
Try adding 2 dried elderberries to the bottle along with the apple for a lovely elderberry flavor.