Line up 4 (25 ounce) bottles with flip top lids or other air tight bottles.
Puree bananas with a fork.
Pour ½ cup banana puree, 2 tablespoons maple syrup, and 1 teaspoon vanilla extract into each 25 ounce bottle.
Using a funnel, pour freshly made homemade kombucha into each 25 ounce bottle leaving 1-2" head space.
Let bottles sit out (at 75° - 85°) 3-5 days, making sure to pop the lids each day to let out the pressure of the carbon dioxide. Taste each day to test its flavor and fizziness.
Notes
Use homemade kombucha that has not been refrigerated yet.