What is the effect of pre-infusion during espresso extraction?

Pre-infusion is a technique used in espresso extraction that has a significant impact on the quality of the espresso. The correct answer highlights that pre-infusion allows the coffee grounds to expand and release carbon dioxide, which is crucial for achieving optimal extraction.

When hot water is introduced to the coffee grounds at a lower pressure, this gentle initial contact causes the grounds to swell and expand. This expansion helps to evenly saturate the coffee, ensuring that the water flows uniformly through the coffee puck during the extraction. Additionally, as the grounds expand, trapped carbon dioxide that may have built up during the roasting process is released. This release is important because excess carbon dioxide can create undesirable flavors in the final cup if not properly managed.

The benefits of pre-infusion include improved flavor extraction, a more balanced profile, and reduced risk of channeling, where water flows unevenly through the coffee grounds. An even extraction yields a more nuanced espresso, highlighting the beans' inherent flavors.