Kombucha (also tea mushroom, tea fungus, or Manchurian mushroom when referring to the culture; botanical name Medusomyces gisevii Lindau) is a fermented, slightly alcoholic, lightly effervescent, sweetened black or green tea drink commonly intended as a functional beverage for its supposed health benefits. Sometimes the beverage is called kombucha tea to distinguish the name from the kombucha culture of bacteria and yeast.
Kombucha is produced by fermenting tea using a "symbiotic culture of bacteria and yeast" (SCOBY) commonly called a "mother" or "mushroom". The microbial populations in a SCOBY vary: the yeast component generally includes Saccharomyces cerevisiae, along with other species, while the bacterial component almost always includes Gluconacetobacter xylinus to oxidize yeast-produced alcohols to acetic acid (and other acids). Although a SCOBY is commonly called tea fungus or mushroom, it is actually "a symbiotic growth of acetic acid bacteria and osmophilic yeast species in a zoogleal mat [biofilm]". The living bacteria are said to be probiotic, one of the reasons for the drink's popularity.
The exact origins of kombucha as a drink are not known. It is thought to have originated in the area of Northeastern China, and was traditionally consumed there, but also in Russia and eastern Europe. Kombucha is now homebrewed globally, and is also sold commercially by various companies.
Numerous implausible claims have been made for health benefits from drinking kombucha. These include claims for treating AIDS, aging, anorexia, arthritis, atherosclerosis, cancer, constipation, and diabetes, but there is no evidence to support any of these claims. There have been rare cases of serious adverse effects, including fatalities, from the beverage, possibly arising from contamination during home preparation. The potential harms of drinking kombucha outweigh the unclear benefits, so its use for therapeutic purposes is not recommended by doctors.