Boil 4 cups of water in a medium sized pot.
Steep loose leaf black tea in hot water for 5-6 minutes (for stronger flavor, leave longer).
Stir in 1 cup of white sugar until completely dissolved.
Strain black tea using cheesecloth (keep the other piece of cheesecloth for later).
Pour tea mixture into one gallon glass brewing jar of your choice.
Fill the glass brewing jar with 8 cups of cold, filtered, unchlorinated water. Your jar should be 3/4 full to leave room for SCOBY and starter tea.
Cool down the tea mixture to room temperature (the brew must be room temperature for the next step).
Add SCOBY and starter tea to the tea mixture.
Cover and secure the jar with remaining cheesecloth and twine.
Leave the brew to sit at room temperature for 7-12 days, out of direct sunlight, and in an area with adequate airflow. Kombucha will not ferment in colder temperatures.
Watch the brew ferment and form a new cream-colored layer in 7-12 days. This is your brand-new SCOBY.
Taste your batch with a clean spoon. If it is too sweet, you can let it brew a little longer. Over time, kombucha will become less sweet and more sour.
Bottle kombucha without SCOBY into a glass bottle and refrigerate to enjoy it cool. Ensure that the bottle is sealed shut and leave 1-2 inches of space at the top for carbonation. Kombucha will continue to ferment in the bottle but at a slower rate in the refrigerator.