Bring 8 cups water to a rolling boil, then immediately turn off the heat. Stir in the loose-leaf black tea and 1 cup sugar, stirring until it dissolves completely. Allow the tea to steep for 10 to 15 minutes, and then strain.

Let the sweetened tea cool to room temperature. Then pour it into a gallon-sized jar. Stir in the prepared kombucha tea, and then drop in the SCOBY.

Cover the mouth of the jar with a clean cloth or coffee filter and secure it with a rubber band. This allows airflow while keeping out contaminants. Place the jar in a warm, dark place (ideally between 75-85 F or 24 29 C) to ferment. Avoid direct sunlight. Let the kombucha ferment for 7 to 14 days. The longer it ferments, the more acidic and less sweet it will taste.

When the kombucha SCOBY has grown larger and the kombucha tastes pleasantly tart, it's time to flavor it. Set aside the kombucha SCOBY and 1 cup of kombucha tea for a future batch, keep the remaining kombucha tea in its jar.

Bring 2 cups water to a boil in a small saucepan. Turn off the heat, and then stir in the hibiscus flowers and ¼ cup sugar. Let it steep until it cools to room temperature. Then, strain it, pressing the hibiscus flowers to get as much liquid as possible. You should have about ½ cup of sweetened hibiscus tea. Stir the hibiscus tea into the remaining kombucha tea.

Pour it evenly into 4 (16-oz) flip-top bottles and close them tightly. Allow them to ferment for 2 to 3 days, taking care to burp the jars once a day. Then transfer them to the fridge for at least 3 more days before serving. Store the finished kombucha in the fridge and enjoy it within 3 months.