Puck

The puck is the compressed disc of ground coffee sitting in your basket inside the portafilter. You create it by dosing ground coffee, distributing it, and tamping it level. During the shot, pressurized water is forced down through this puck, and how evenly it is built largely decides how the espresso tastes.

Why it matters: the puck is the resistance the water has to work through. If it is dense in some spots and loose in others, water takes the easy path through the weak areas, a fault called channeling that gives uneven, harsh extraction. A well-prepared, uniform puck offers consistent resistance everywhere, so water contacts all the coffee evenly and the shot pours smooth and balanced.

After the shot, you knock the spent puck out into a knock box. Reading it is useful diagnostic feedback: a clean, intact, slightly domed puck suggests a tidy extraction, while a soupy, cratered, or cracked puck points to problems in dose, grind, or distribution. Good puck prep, including WDT and a level tamp, is what turns loose grounds into a reliable puck.