Pre-infusion chamber

A small cavity inside an E61 brew valve that fills with water at line pressure before pumping engages. The expansion of water against a spring-loaded piston creates a natural pre-infusion phase — gentle wetting of the puck before full pressure ramps in.

Why it matters — The pre-infusion chamber is what gives E61 groups their characteristic shot profile. The mechanical pre-infusion is the reason E61 machines have been so durable in the marketplace — they produce great shots without electronic complexity.

Good to know

• Pre-infusion chamber size and spring tension are fixed by design — you can change gicleurs to modify behaviour, but the chamber itself is non-adjustable.
• Some E61 manufacturers (Lelit, Profitec, ECM) offer additional pre-infusion features layered on top of the mechanical chamber.