Tamping
填压
EspressoDefinition
The step of compressing ground coffee into the portafilter basket with a tamper to form an even, level puck before extraction. A level tamp keeps water flowing uniformly through the bed; an uneven one invites channeling, where water punches through weak spots and leaves much of the coffee under-extracted.
Etymology
From the English verb tamp, meaning to pack down with repeated blows. It entered coffee language once manual lever and pump machines made the portafilter standard in the mid-20th century.
In use
"Tamp level, not hard" is common barista advice, since a flat surface matters far more than the force applied.