Ishizuchi-kurocha (石鎚黒茶) is a Japanese post-fermented tea from Ehime Prefecture, in northwestern Shikoku. “Ishizuchi” is the name of the mountain where this tea is grown (the mountain itself is quite high, about 2000 meters, but the tea is grown at the height of six hundred meters, approximately). And “kurocha” means “dark (post-fermented) tea”.
In the middle of summer, to produce ishizuchi-kurocha, shoots (branches with leaves and buds, and the twig part may be very long) are cut from fairly high tea trees. Then the shoots are fixed by steaming, during which the leaves fall off from the branches. After fixation, the tea leaves are placed for 4-6 days in wooden boxes for aerobic fungal fermentation. After that, the leaves are manually rolled and subjected to anaerobic fermentation involving lactic acid bacteria, for 2-3 weeks. Nowadays, for this fermentation, the leaves are placed in plastic bags, from which the air is pumped out. After the leaves are removed from the bags, the tea is dried in the sun.
Ishizuchi-kurocha was originally used as a food ingredient, but now it is often used as an individual drink. Prepared by infusions or short boiling, it is recommended to be served chilled, sometimes on the rocks. People find the aroma of this tea similar to that of GABA-tea with sour fruity notes, but the taste of ishizuchi-kurocha is close to goishicha — sour, but not bitter, with a pleasant aftertaste.
At some point, ishizuchi-kurocha was almost lost, it is believed that there was left only one master who could make this tea. But some enthusiasts have saved the technology of making ishizuchi-kurocha. According to the enthusiasts themselves, their tea does not yet match the original taste, so they call it Tengu-kurocha (天狗黒茶). Tengu is the peak of the Mount Ishizuchi. Such a nontrivial modesty.
Ishizuchi-kurocha is rich in gamma-aminobutyric acid, but it has little theanine and catechins. It is believed to be impossible to buy outside of Japan. Here are a couple of similar tasting notes about this tea: one and two, and the description of the tea on My Japanese Green Tea. And, finally, an excellent illustrated description of ishizuchi-kurocha on Setouchi Finder.