What is the purpose of pre-infusion in espresso making?

The purpose of pre-infusion in espresso making is to saturate the coffee grounds before full extraction, which promotes an even flow and enhances the overall flavor of the espresso. During pre-infusion, a small amount of water is allowed to flow through the coffee grounds at a lower pressure before the main brewing process begins. This initial contact helps to ensure that the coffee grounds are evenly wet, reducing channeling and allowing for a more uniform extraction of flavors.

By pre-infusing, the coffee grounds can expand and degas, which further helps in optimizing the extraction process when higher pressure is applied later. This technique contributes to a balanced and nuanced flavor profile in the final cup, making it a valuable step in espresso preparation.