Add the apple cider, grated apple, grated ginger, and apple stick to a saucepan. Bring to a boil and reduce heat to a simmer. Simmer for 25 to 35 minutes until the mixture reduces by half.
Stir in maple syrup and remove from heat.
Let cool completely before transferring the mixture to freshly brewed kombucha.
Notes
*The mixture makes 1 cup. A batch of kombucha will yield about 14 cups (because you reserve 2 cups for the next batch). You can bottle in half gallon containers or 16 ounce containers. Add equal amounts to each cup depending on size of the container. (Half gallon container will use ½ cup mixture for each. 16 ounce container will use about 2 tablespoon for each)