Bring the water to a boil, and remove it from the heat source. Add in the sugar, stirring until it is all dissolved. Immediately afterwards add in the tea bags.
Seep the tea for around 10 minutes. (I use a mixture of green tea and black tea and remove the green tea bags a couple of minutes before the black tea bags.)
Remove the tea bags and let the sweetened tea cool to room temperature.
Add the sweetened tea to a large glass container, topping it off with some starter kombucha. If you don't have any starter kombucha or kombucha from your last batch, you can also use apple cider vinegar to help lower the pH and help prevent mold from forming on the SCOBY.
Cover the glass container with a cloth that will let the mixture breath but will keep out dust and insects. I secure a square of cotton cloth over my gallon sized jar with a rubber band, but you could also use something like a coffee filter instead.
Store the mixture undisturbed for a week before tasting it. Ideal temperatures for kombucha brewing are somewhere between 70º-80ºF. That doesn't mean that you can't brew kombucha if you have temperatures higher or lower than that in your house. The only problem is that outside 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 for the temperature.
Above 80ºF, you are more likely to throw off the balance of your kombucha. The Kombucha SCOBY is a symbiotic colony of bacteria and yeasts, remember? If the temperature is too high, though, you could throw off the balance in the favor of too many yeasts in the mixture.
Kombucha can be rebalanced if you have that problem, but that will have to be the subject of another post some other day.
Your kombucha is ready when it has reached the desired level of fermentation. As the days go by the kombucha will no longer taste like sweet tea, but instead will become more and more sour. Most people prefer kombucha after around 7-10 days of fermentation. If it's winter and you are brewing in cooler temperatures, you'll probably find that you want to ferment longer than that. The same goes for the first time you are fermenting, especially if you don't have as much starter kombucha.
If it's hot out, you'll probably want to stop after a week or so.
To taste the kombucha, try not to disturb the newly forming SCOBY on top of your liquid. 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, take out your SCOBYs. (You'll probably have your original SCOBY and a newly formed one floating on top, but you may have new layers on your original SCOBY if it was floating to begin with, or you may not have developed much of a new one, which we can troubleshoot some other day.)
Pour the kombucha into bottles. I like glass bottles with flip cap type stoppers. Remember to save at least a cup of your kombucha to use as a starter for your next batch!
Once you have your kombucha bottled, you can drink it immediately, but I prefer to do a second fermentation first.
To do a second fermentation, leave the bottles tightly capped at room temperature.
After a few days, you'll probably notice that your kombucha is now much more carbonated. If you are having problems achieving a desired level of carbonation, you can add some fruit to your kombucha during the second fermentation to help out the process while you flavor it.
Once you've reached the desired carbonation level, place your bottles of kombucha in the fridge.
It's a good idea to occasionally "burp" the bottles of kombucha. This is done by opening them every couple of days to let out any excess gas. 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.
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.)