Pre-infusion wets the coffee at low pressure for a few seconds before the pump reaches full pressure.
What it does
The dry puck expands as it absorbs water. Hitting a dry puck with 9 bars immediately can fracture it, and a fractured puck channels.
Letting it wet gently first means the bed is saturated and settled when full pressure arrives.
The benefits
Fewer channels, which is the main one. More even extraction, so the shot tastes cleaner. More forgiving of imperfect puck prep — it partly compensates for distribution errors. Often allows a finer grind without choking, which raises extraction.
How long
3 to 8 seconds for most setups. Light roasts often benefit from longer.
Too long and you start losing temperature and extracting unevenly at low pressure.
How machines do it
Line pressure pre-infusion — water-line pressure of 2 to 4 bar, on machines plumbed in or with a solenoid arrangement. The classic E61 approach.
Programmed — the pump runs briefly, pauses, then ramps. Common on modern machines.
Manual, on a lever machine or with flow control — you decide.
Spring-loaded portafilters and some baskets approximate it.
Without any of that
You can approximate it on many basic machines: start the pump, stop it after two or three seconds, wait about five, then resume. It is a genuine improvement, not the difference between good and bad coffee. Good puck prep — WDT and a level tamp — addresses the same problem from the other end and matters more.
Last reviewed 30 October 2026