A super flexible kombucha's 2nd fermentation recipe to make the kombucha carbonation and flavour you desire.
Filter your mature acidic kombucha through a coffee filter. This is to remove dead yeast strands in the kombucha from the 1st fermentation. Note that more dead yeast will appear at the end of the 2nd fermentation again. However, filtering the dead yeast now will reduce the amount in the final product.
Fill your flip-top bottle with the filtered kombucha. If you are not planning to add fruit juice later, you can add more kombucha to fill the capacity of the bottle.
Use any flavour combination from the ingredient list above. You don't need to use all of the juice, fruits, ginger, herbs, spices and sweetener. Choose a combination and the amount that suits your taste. Add your chosen ingredients to the kombucha bottle, make sure to leave at least an inch of air space on top.
Close the bottle tightly. Let it ferment until it reaches the level of kombucha carbonation you desire. Typically 3-7 days in room temperature between 21º and 29ºC. But could be less or more. See the "kombucha carbonation tips" section for details.
Move to cold storage when the 2nd fermentation is done. Your fizzy flavoured kombucha will last in cold storage forever!