preinfusion

Preinfusion, also known as bloom or wetting, is a preparatory step in some coffee brewing methods, most notably espresso. It involves a brief period where hot water is introduced to the coffee grounds before the full brewing pressure is applied. This initial wetting allows the coffee bed to saturate evenly and enables the release of trapped gases, primarily carbon dioxide, which is a byproduct of the coffee roasting process.

During roasting, significant amounts of CO2 are created within the coffee bean structure. When hot water first contacts the grounds, this CO2 rapidly escapes, often in the form of a visible bloom or bubbling. If this degassing phase is skipped, the CO2 can interfere with the even extraction of soluble coffee compounds during the main brewing phase. The gas pockets can create channels through the coffee bed, leading to uneven water flow and inconsistent extraction, resulting in a less flavorful and potentially sour or bitter cup of coffee.

The duration of preinfusion can vary depending on the brewing method and desired outcome. For espresso, a typical preinfusion might last from a few seconds to around 10 seconds. This allows the coffee puck to swell slightly and become fully saturated, preparing it for the higher pressure extraction that follows. In other methods like pour-over, a similar wetting phase is also crucial for achieving optimal flavor. The benefits of preinfusion include a more balanced extraction, enhanced sweetness, and a more complex flavor profile.