Make the sweet tea base: Bring 1 quart of the water to a rolling boil. Add the sugar and stir until the sugar has dissolved. Remove the pot from heat and add the tea. Let stand for at least 10 minutes to steep the tea.

Remove the tea.

Combine all the liquids in a 1-gallon glass jar: Pour the sweet tea into a 1-gallon jar and add the remaining 2 ½ quarts of water. Check the diluted sweet tea mixture with a clean finger to make sure it has cooled sufficiently before adding the prepared kombucha or the scoby; it should be lukewarm (or cooler) to the touch. If it still feels hot, wait for it to cool before continuing. Stir the prepared kombucha (store bought or saved from a previous batch) into the diluted sweet tea.

Slip the scoby into the jar of liquid. Cover the jar with a cloth and secure with a rubber band.

Place the jar somewhere out of the way, away from direct sunlight, and at a steady room temperature: Check it every so often over the next week or two. Kombucha ferments best between 70°F and 75°F. Warmer temperatures make it ferment more quickly and cooler temperatures make fermentation slow down.

Let the kombucha ferment for 7 to 14 days, or until it tastes good to you: Start tasting the kombucha after a few days. In the first few days of fermentation, the kombucha will taste like sweetened tea, but then it will gradually become more tart and vinegary the longer it ferments.

Remove the scoby and set aside: Pour out 2 cups of your kombucha and pour it over the scoby. Use this as your 'prepared kombucha' for your next batch.

At this point, you can either start a new batch of kombucha right now using this scoby and liquid, or you can cover the bowl and keep the scoby and liquid at room temperature until you’re ready to make another batch. (You can store your scoby this way for up to a month or two; add additional sweetened tea as needed to keep the scoby covered.)

Bottle the remaining kombucha: If you like, add some juice, chopped fruit, fresh herbs, or spices to each bottle to flavor the kombucha. Cap each bottle tightly. Wait for your kombucha to carbonate: Check each day by opening up one of the bottles. When you hear a soft pop! and see bubbles flowing to the surface of the liquid after you open it, it's ready!