Goishicha ( ja, 碁石茶 ' go-pebble tea') is a

fermented tea Fermented tea (also known as post-fermented tea or dark tea) is a class of tea that has undergone microbial fermentation, from several months to many years. The exposure of the tea leaves to humidity and oxygen during the process also causes ...

originally from China but now grown only in

Ōtoyo, Kōchi is a List of towns in Japan, town located in Nagaoka District, Kōchi, Nagaoka District, Kōchi Prefecture, Japan in the mountainous district of central Shikoku. The and both flow through Ōtoyo. It is the only municipality in Shikoku where ove ...

and Ishizuchi-Kurocha,

Ehime prefecture is a prefecture of Japan located on the island of Shikoku. Ehime Prefecture has a population of 1,342,011 (1 June 2019) and has a geographic area of 5,676 km2 (2,191 sq mi). Ehime Prefecture borders Kagawa Prefecture to the northeast, Toku ...

. The tea is made by fermenting harvested tea in a two step process, first with aerobic fungi, then with anaerobic bacteria.

References

Fermented tea Japanese tea {{tea-stub