SCOBY

SCOBY stands for symbiotic culture of bacteria and yeast, and it is the rubbery, disc-shaped culture that sits at the surface of a batch of kombucha. It forms as bacteria and yeast work together, the yeast breaking down sugar and producing alcohol, and the bacteria converting that alcohol into acids, which is what gives kombucha its tart, slightly vinegary flavor.

A healthy SCOBY is typically pale, off-white, or tan, and can be smooth or have stringy yeast strands hanging from its underside, which is normal. Each time you brew a new batch, the SCOBY produces a new layer, so over time a single culture can grow thick or even split into extra layers that some brewers peel apart to share or store as backups in what is often called a SCOBY hotel.

New brewers sometimes confuse a normal SCOBY with mold, but genuine mold on kombucha usually looks fuzzy and appears on top, in a color that is distinct from the pale culture underneath, rather than being part of the rubbery mat itself. Starting with a SCOBY and some starter liquid from an established batch, rather than trying to grow one from scratch, tends to give far more consistent early results.