What saponins means
Saponins are amphiphilic plant compounds that lower the surface tension of water and stabilize air bubbles, which is why a properly whisked usucha holds a fine, even foam. Tea saponins are concentrated in the leaf and are released into the bowl as the chasen aerates the suspension. Studies of Camellia sinensis identify several teasaponin variants, and their presence is part of why matcha foams readily where steeped tea does not. The foam fades as saponin films break down, so usucha is meant to be drunk soon after whisking.
Also called
Saponins also appears as tea saponins, teasaponin.