Ishi-usu
The traditional granite stone mill used to grind tencha into matcha.
Also known as: matcha stone mill, granite mill
An ishi-usu is a hand-cut granite stone mill used to slowly grind tencha into the fine powder we call matcha. Two large discs rotate against each other at low RPM, with grooved channels guiding the ground leaf to the outer edge. The slow speed prevents heat — heat would scorch the leaves and dull both color and flavor. A traditional ishi-usu produces only 30 to 40 grams of matcha per hour, which is most of why high-quality matcha isn't cheap. Modern producers also use ceramic or electric mills, which are faster but considered to produce less nuanced matcha.