What Is Pre-Infusion?
Pre-infusion is the gentle pre-wetting of coffee in your portafilter before extracting. On the Quick Mill Vetrano Design, there are several ways that you can pre-infuse your shots of espresso before brewing.
Pre-infusion is what allows a small amount of water through first, before beginning the shot. It allows this water to saturate the coffee and get the grounds equally wet. This can make the coffee extract more smoothly. Water will always take the path of least resistance. By letting the water saturate the grinds before brewing at 9 bars of pressure, this can help prevent channeling.
How To: Pre-Infusion on E61 Brew Group Espresso Machines