Espresso is a high-pressure extraction through a thin bed, and small variations have large effects.
The controllable ones
Dose. Weigh into the basket, every shot, to 0.1 g. Timed grinding drifts as the hopper empties and as beans change.
Distribution. Clumps cause channelling, and channelling is the single biggest source of shot-to-shot variation. Use WDT — stir the dry grounds with fine needles before tamping.
Tamp. Level matters far more than force. A tilted tamp guarantees a channel.
Yield. Weigh the output. Timing alone does not tell you what came out.
The machine ones
Temperature stability. Single-boiler machines drift several degrees between shots. Surfing the temperature or fitting a PID helps.
Warm-up. A machine needs 20 to 30 minutes to reach thermal equilibrium, not the 3 minutes the ready light suggests.
The first shot. Almost always different. Pull one and discard it, or accept it.
The bean ones
Age. A bag changes measurably over its life. Days 3 to 7 behave differently from days 20 to 25, and it needs re-dialling.
Humidity. Coffee absorbs atmospheric moisture, which changes how it grinds. Damp days genuinely run slower.
The order to fix them
Weigh in. Weigh out. WDT. Then worry about the machine.
Last reviewed 8 August 2026