A Symbiotic Culture of Bacteria and Yeast.
The physical scoby is basically a house for all the good bacteria and yeast that ferment kombucha. The slimy scoby is cellulose that is produced by the bacteria and yeast present in the starter culture. This is why the starter culture liquid in your Mad Millie scoby or from your previous brew is so important, the microorganisms don’t just live in the cellulose, they also live in the brew itself.