I posted a response a while ago on another thread, but I thought I'd respond to this one as well. I've been brewing kombucha for over a year, I've made some observations and a few adjustments I'd like to share with you. I love to bend the rules to find out WHY others tell me "don't do that", so bear with me:
First, though kombucha is traditionally brewed with black tea, you can use most any kind of tea; caffeine, decaf, or even herbal. Avoid oily herbal tea mixes. I personally prefer kombucha brewed with green tea and not black (tastes better to me.)
(Note: all temperatures are in Fahrenheit)
Second, I used to boil the water for 10 minutes to sanitize it, but I found that green tea (the kind I use) tastes better when the water is heated to 180 degrees and not boiled. Since I'm making a gallon or so, the water will stay that way longer than the amount of time it takes to sanitize.
Third, I use 1 and a half cups sugar per gallon of water. I usually add it before the water gets to temperature- say, around 160 degrees or so, so that it will dissolve faster, then stir until it disappears. As for the tea- I use 6 average-sized tea bags per gallon of water. I let it steep for 20 minutes after remving the pot from the heat. The purpose of the tea is not what you think. It just brings the pH to an ideal level for the kombucha "SCOBY" (Symbiotic Colony Of Bacteria and Yeast) to thrive and consume the sugar.
Finally, I cover the pot with its lid and let it sit overnight to let it cool. I've let the pot sit 24 hours before with no problem. When you're ready, just pour in a 20 oz bottle of unpasteurized kombucha (G.T.'s is a good choice, Kombucha Wonder Drink is pasteurized), then transfer the mixture to a glass container. cover the container with a tea towel (linen napkin like used in restaurants) and secure with a rubber band.
The first batch takes about 10 days to mature at about 75-80 degrees. My kombucha has lived in temps as low as 60 degrees or so, but it develops slower. Just keep it at whatever your room temperature is and you should be fine.
When it is mature, you can either drink and replace as you go, or you can bottle it, hold back 2 cups reserve per gallon (plus the "mushroom" that forms), and start another batch. I mix mine with fruit in a Vitamix then bottle in beer bottles. It will get fizzy after a couple of days, then you should refrigerate or else kaboom.
Note: unlike brewing beer which needs to be handled with surgical cleanliness, kombucha is pretty aggressive and most foreign buggies pretty much leave it alone. But be clean anyway to avoid headaches and possible mold.