Pre-Infusion

Pre-infusion is a brief, low-pressure phase at the beginning of an espresso extraction where water is introduced to the coffee puck at reduced pressure before the pump ramps up to full 9-bar brewing pressure. The purpose is to evenly saturate the grounds and fill any voids in the coffee bed before the main extraction begins, reducing the risk of channeling.

During pre-infusion, water gently soaks into the compressed puck at typically 2 to 4 bars or even line pressure (about 1.5 bars in most plumbing systems). This saturation phase allows the coffee to expand uniformly and seal any gaps that could become channels under full pressure. A well-pre-infused puck extracts more evenly, producing a more balanced, sweeter espresso with less risk of bitter or sour notes from uneven extraction.

Pre-infusion methods vary by machine design. E61 group heads have a built-in mechanical pre-infusion chamber that naturally ramps up pressure. Plumbed-in machines can use line pressure for pre-infusion by opening a valve before engaging the pump. Some advanced machines offer programmable pre-infusion where the user sets the duration, pressure, and ramp profile.

The duration of pre-infusion typically ranges from 2 to 8 seconds, though some long pre-infusion techniques extend to 15 seconds or more for very light roasts that benefit from slower, gentler water contact. Pre-infusion is especially helpful when grinding finer or using lighter roasts, which are more prone to channeling than darker roasts. Most modern prosumer and commercial machines include some form of pre-infusion as a standard feature.