What is a SCOBY in kombucha making?

A SCOBY is a symbiotic culture of bacteria and yeast. This is what allows the fermentation process to occur to make kombucha and is often referred to as the kombucha starter. The bacteria and yeast in the SCOBY convert the sugar present in the sweet tea used to make alcohol, and also creates the fizziness typical in kombucha. Often the pellicle that forms on the top of the kombucha liquid is referred to as the SCOBY but this is a heated topic amongst many kombucha makers if that is necessary to include as a starter when brewing your next batch of kombucha.