Makes 2 liters
Prep time: 15 minutes
Total time: 7 to 10 days
240 grams sugar
1.76 kilograms water
730 grams leftover coffee grounds, or 200 grams freshly ground coffee
200 grams unpasteurized kombucha (or the liquid that comes with a packaged SCOBY)
1. Bring the sugar and 240 grams of the water to a boil in a medium pot, stirring to dissolve the sugar.
2. Meanwhile, put the coffee grounds in a nonreactive heatproof container. Pour the hot syrup over the coffee, then add the remaining 1.52 kilograms water. Let the coffee mixture cool to room temperature, cover, and transfer to the fridge to infuse overnight.
3. The following day, strain the coffee liquid through a fine-mesh sieve lined with cheesecloth into the fermentation vessel. Backslop the infusion by stirring in the 200 grams unpasteurized kombucha.
4. Wearing gloves, carefully place the SCOBY into the liquid. Cover the top of the fermentation vessel with cheesecloth or a breathable kitchen towel and secure it with a rubber band. Label the kombucha and set it in a warm place.
5. Leave the kombucha to ferment, tracking its progress each day. Make sure the top of the SCOBY doesn’t dry out; use a ladle to moisten it with some of the liquid, if necessary. Once you’re happy with the flavor of your kombucha—probably between 7 and 10 days from the start—transfer the SCOBY to a container for storage and strain the kombucha. Consume immediately or refrigerate, freeze, or bottle it.