Tea Ceremony & Extraction9 min · 2026-03-08

Koicha isn't foamed: usucha's fine texture and the chasen's prong count

Koicha is high in viscosity and solids, so the chasen's motion is closer to 'loosening.' In usucha, by contrast, fine foam becomes one with the texture of umami. From measured notes in the tea room: the interplay of the chasen's prong count and stiffness with water hardness.

Koicha is closer to 'loosening' with the chasen, and foam is considered unnecessary. Because viscosity is high, the chasen is moved as if grazing the bottom of the bowl; stir too much and sediment appears.

In usucha, the chasen's prong count and stiffness directly govern how fine the texture is. Hard water makes coarse foam; soft water makes it fine but short-lived — water quality deserves recording as a variable for reproducibility, even in the tea room.