Processing
Mushi (steaming)
Steaming the picked leaf to kill the oxidizing enzymes. This is the decisive difference from Chinese green tea, which is pan-fired instead. 20–60 seconds is asamushi (light); 60–120 seconds is fukamushi (deep). The deeper the steam, the more the leaf breaks down: darker liquor, softer astringency.
In more detail
Light steaming leaves the leaf intact, giving a clear yellow-green liquor and a lifted aroma. Deep steaming breaks it down, producing fine particles, a cloudy deep green cup and rounder astringency. Neither is better; they are different preferences. Deep-steamed tea clogs fine strainers, so a kyusu with a coarse sasame mesh makes it easier to handle.