When discussing espresso, pre-infusion refers to the process of adding water to ground coffee. Pre-infusion is the initial wetting and expanding of the coffee puck in the portafilter with low-pressure water before using the full eight to eleven bars of pressure for espresso extraction. During the pre-infusion process, water is used in moderation, just enough to evenly wet the puck. It is ideal to do so at a lower pressure and higher temperature than those employed in the extraction process. The result of pre-infusion is minimized channeling and more even extraction, theoretically leading to better tasting espresso.
Why is pre-infusion useful?
The main purpose of pre-infusion is to help mitigate potential problems that arise during the tamping process. During your espresso prep, if you've ever noticed cracks or air pockets in the coffee puck, then you may have failed to collapse and distribute the coffee grounds properly. Alternatively, if you tamped unevenly, perhaps there is a spot less dense than the rest of the puck. Channeling may occur if eight to eleven bars of water pressure is applied directly to a coffee puck with these issues. Using a channeled coffee puck will result in an over-extracted coffee with bitter flavors.
By pre-infusing the coffee, it will absorb the water evenly during the brewing process, avoiding channeling. This is because water flows through a small area of the puck rather than spreading evenly. By pre-infusing, you get an even flow rate and thus, a more consistent extraction.
How does pre-infusion work exactly?
In the portafilter, the coffee puck is evenly soaked with water during pre-infusion. After absorbing the water, it expands. This essentially presses the grounds against each other and against the portafilter walls. This process is known as blooming and aids in sealing any holes or micro-cracks.
The resulting pressure from the grouphead during extraction will keep the puck intact, prevent channeling and extract evenly through the portafilter. The end cup is rich, flavorful and full of aroma!
How long do I set pre-infusion for?
To answer this question, you will first need to know the ins and outs of your coffee beans. Important factors to consider are the roast level, country of origin, whether it’s a blend or a single origin. These will all affect the final taste in some minor way.
Another factor is the type of espresso machine you are using. Dose volume can also play a part. Dosing for a single shot may be slightly different than dosing for a double shot.
To summarize, getting to know your espresso machine is the first step in the pre-infusion journey. The widely accepted pre-infusion time is between two and eight seconds. Experiment and adjust as necessary to find your perfect cup!