3 1/2 quarts water
1 cup white sugar
4 bags black tea (or 1 tablespoons loose tea)
4 bags green tea (or 1 tablespoon loose tea)
2 cups pre-made unflavored kombucha (from your last homemade batch or store-bought)
1 scoby per fermentation jar
2- to 3-inch piece fresh ginger (See recipe note)
Special equipment: Six 16-oz glass bottles with plastic lids, swing-top bottles, or clean soda bottles
Bring the water to a boil. Remove from heat and stir in the sugar to dissolve. Drop in the tea and allow it to steep until the water has cooled. Depending on the size of your pot, this will take a few hours. (Alternatively, you can speed this up by boiling only half the water, letting the tea steep, and then cooling it down with the remaining water.)
Once the tea is cool, remove the tea bags (or strain out the loose tea). Stir in the pre-made kombucha. (This makes the tea acidic, which prevents unfriendly bacteria from taking up residence in the first few days of fermentation.)
Pour the mixture into a 1-gallon glass jar and gently slide the scoby on top with clean hands. Cover the mouth of the jar with a few layers of cheesecloth or paper towels secured with a rubber band. (You can divide this between several jars instead of one big one, but each jar will need its own scoby.)
Keep the fermenting kombucha at room temperature, out of direct sunlight, and where it won't get jostled. Ferment for 7 to 10 days, checking the kombucha and the scoby periodically.
After 7 days, begin tasting the kombucha daily by pouring a little out of the jar and into a cup. When it reaches a balance of sweetness and tartness that is pleasant to you, the kombucha is ready to bottle.
With clean hands, gently lift the scoby out of the kombucha and set it on a clean plate. If you're planning to make another batch of kombucha right away, measure out your starter tea from this batch of kombucha and set it aside for the next batch.
Scrub the ginger clean, but don't bother peeling it. Grate it finely on a microplane or chop it finely in a food processor; be sure to catch any juices that collect. You should have 1 1/2 to 2 tablespoons of ginger puree and juice. Divide the ginger evenly between all your bottles. (Personally, I love about 1 teaspoon of ginger per bottle!)
Pour the fermented kombucha (straining, if desired) into the bottles using a small funnel. Leave about an inch of head room in each bottle. Store the bottled kombucha at room-temperature out of direct sunlight and allow 1 to 3 days for the kombucha to carbonate. If you bottled in plastic bottles, the kombucha is carbonated when the bottles are rock-solid; if you bottled in glass, intermittently open one of the bottles to check the carbonation (it will re-carbonate quickly once you put the cap back on).