Kombucha may have originated in the Bohai Sea region of China, but the history is not well documented. Popular legends locating its invention at the Qin dynasty imperial court, or crediting a Korean physician who supposedly brought it to Japan, are not supported by evidence and are treated by historians as apocryphal.
What would resolve this A securely dated pre-19th-century written or archaeological record describing the fermented tea culture in China, or elsewhere, rather than the undocumented Bohai Sea attribution and the debunked Qin dynasty and Korea-to-Japan legends, would fix where and when kombucha began.
OpenCulinary history / food fermentation historyKombucha (Wikipedia)