What is pre-infusion and how can it benefit my extraction?
Pre-infusion is the act of saturating the coffee cake with brew water at a low pressure, typically around 1-2 BAR, for a short period of time, usually 8-10 seconds, before ramping to full pressure. The goal is to evenly soak the entire puck without kicking-off extraction which would be categorized by a measurable accumulation of extracted beverage in the cup. By doing so, you can achieve higher extraction rates and minimize the occurrences of channels forming in the coffee bed when higher pressure is later applied.
By monitoring the filter basket from below while brewing bottomless, you can accurately control the low-pressure pre-infusion and prevent extraction from occurring by backing off the lever when you see the first drops beginning to push through the filter. To introduce pre-infusion into your brew, slowly pull the lever down until 1-2 BAR is reporting on the gauge, then modulate the active force to keep it there for the remainder of time you are targeting. Once you have reached the desired pre-infusion time, move forward with extraction as normal. If you are unable to hold back flow for the desired time, grind finer until you can.
It’s important that you do not abruptly release the lever or active force in between pre-infusion and extraction phases: Simply apply low-pressure, hold or modulate as needed, then ramp to high-pressure and complete the pull. For the o-rings installed inside the cylinder to engage and seal against the portafilter, the commencement of the pull must be marked with a constant and firm force on the lever. Should the forces applied to the lever waver or diminish significantly e.g. pumping the lever, the cylinder may rise up in an attempt to release pressure through expansion of the brew head, and result in separation of the brew components. Never pump the handle.
If you do not wish to include a pre-infusion in your brew, we recommend a slow ramp up from “0” to your desired brew pressure. Always continue in the direction of the pull once you have started.