Bring the water to a boil, and remove it from the heat source. Add the sugar, stirring until it is all dissolved. Immediately afterward, add the tea.
Seep the tea for around 10 minutes.
Remove the tea bags and allow the sweetened tea fully cool to room temperature.
Fermenting the kombucha
Add the cool, sweetened tea to a large glass or food-safe ceramic container. Top it off with some starter kombucha from a previous batch. If you don't have any starter kombucha or kombucha from your last batch, you can also use spirit vinegar to help lower the pH and help prevent mold from forming on the SCOBY. (Other vinegars may contribute new microorganisms to the SCOBY and kombucha.)
Cover the glass container with a clean cotton cloth or coffee filter. This allows the mixture to breathe while keeping out dust and insects. Secure the cloth over the mouth of the jar with a rubber band.
Store the mixture at room temperature undisturbed for a week. After a week, you can begin tasting the kombucha for doneness.
Your kombucha is ready when it has reached the desired level of sourness. As it ferments, the kombucha will become increasingly sour. Most people prefer kombucha after around 7-10 days of fermentation. In cooler temperatures, you may want to ferment longer than that. If it's hot out, you may want to stop earlier.
When tasting the kombucha, try not to disturb the newly forming SCOBY on the surface. You can slide in a straw along the edge of the jar into the kombucha and pull some liquid out to taste it.
Once you've made a Kombucha to your liking, remove the SCOBY(s). (You should have a newly formed SCOBY on top, but it may fuse to the original SCOBY, forming new layers instead.)
Bottling the kombucha
Pour the kombucha into bottles. I like glass bottles with flip cap type stoppers. You can drink it immediately and store in the fridge if you like. (Remember to save at least a cup of your kombucha to use as a starter for your next batch!)
The second fermentation
A second fermentation adds carbonation to the kombucha and can also be used to flavor it. To do a second fermentation, leave the kombucha at room temperature in bottles with airtight lids.
After a day or two (temperature dependent), you'll probably notice that the kombucha is now much more carbonated. To add even more carbonation (and flavor), add some fruit to the kombucha during the second fermentation.
Once you've reached the desired carbonation level, strain out the fruit and store in clean, airtight bottles to keep the carbonation. Store them in the fridge to slow the fermentation process.
Serve chilled and enjoy!
(You can strain out the yeast strings that may form if you prefer, or just leave them in and drink them.)
You should use glass or ceramic jars for brewing kombucha. I use glass gallon jars, adding less than a gallon of water (tea) to allow space for the SCOBY and kombucha starter. Ceramic fermenting crocks also work well for fermenting kombucha. You can easily adjust the ratios to fit whatever container you plan on using.
While you can use either black tea or green tea, I actually like to use a 50/50 mixture for my kombucha. Some people are more successful with one type of tea or the other. I find either works well for me, but just prefer the flavor when using a combination. Black tea makes a more active fermentation and green tea has a milder flavor. Choose accordingly.
Ideal temperatures for kombucha brewing are somewhere between 70º-80ºF. Outside of that temperature range, you are more likely to run into problems. When it is colder than 70ºF, the brewing process will take longer, and it is more likely that you will develop mold. You can add in more starter liquid to help compensate. Above 80ºF, you are more likely to throw off the balance of your kombucha in favor of yeasts.
It's a good idea to occasionally "burp" the bottles of kombucha during the second fermentation and when storing it. This is done by opening the lid to allow the escape of excess gas. (This should be done daily during the second fermentation, and every few days/weeks when stored in the fridge, depending on its level of carbonation.) It's best to use glass bottles to avoid toxins from seeping into your kombucha, but glass is also more susceptible to breaking, so this is merely done to prevent them from exploding, which could happen if the kombucha continues to ferment without letting out the extra carbonation.