Wikipedia
A SCOBY (for symbiotic colony of bacteria and yeast) is a mix of cultures of bacteria and yeast present during production of kombucha and water kefir among others. The term " colony" in the name is scientifically a misnomer, because it implies a group of genetically identical or nearly identical organisms living together. For this reason, the acronym is essentially absent in the biomedical literature and the proper name pellicle is used. The species comprising the mixed cultures vary from preparation to preparation, but generally include Acetobacter bacterial species, as well as various Saccharomyces and other yeast types. SCOBY cultures used in beverage production can produce a structure referred to as a "mushroom," which is also biologically misleading, because mushrooms are a completely unrelated group of fungi. It often forms in vinegar in jars of pickled foods.