A: Before you throw your batch out, make sure it's actually mold! Yeast bits can often times appear blue, green, or even pink, and look like mold. Check out our gallery of healthy/unhealthy cultures. If you're still not certain, send us a picture at firstname.lastname@example.org and we can give you a second opinion.
The number one cause of mold is when the starter tea gets weakened. This means the sweet tea liquid was too hot before the scoby and starter tea were added to the batch in the beginning.
Another possibility is that the average brew temperature during fermentation is too cold. Brewing below 68 degrees can lead to mold as the yeast and bacteria grow so sleepy that they stop fermenting and airborne microbes are allowed to take over.
Other causes are using teas with oils in them - we recommend only using plain black/green/oolong/white teas. Always using at least some black tea as the base with a little bit of green tea for flavor (as opposed to doing just all green tea) will produce the most healthy culture and brew, as black tea is stronger in important nutrients for the scoby.
Also, make sure to use only refined/granulated sugar when brewing.
Lastly, if your culture grew mold on it during storage, this means the top of the culture was exposed to too much oxygen and didn't have enough starter tea to rest in. Next time, leave at least 2-3 cups of liquid starter tea so that you can push the culture down into the liquid, leaving it more protected.
Other than those reasons, it's always possible that airborne molds can float over from kitchen produce, house plants, etc. and get in your brew jars. Try storing your brew jars in a more sterile area of the kitchen or house.