Using pre-ground coffee in an espresso machine is possible, but generally not recommended for optimal results. Espresso machines are designed for finely ground coffee, specifically tailored to create the necessary resistance for proper extraction under pressure. Regular pre-ground coffee is often coarser, leading to under-extraction and a weaker, less flavorful shot. Additionally, using inconsistent grinds can lead to channeling, where water takes the path of least resistance through the coffee puck, resulting in an uneven extraction and a bitter, sour, or otherwise unbalanced taste.
Achieving the rich crema and complex flavors characteristic of a good espresso relies heavily on freshly ground beans and precise grind size. Freshly ground coffee retains more of its volatile aromatic compounds, contributing to the overall sensory experience. Historically, espresso preparation has emphasized this freshness and control over the grind, evolving from early lever machines to modern pump-driven systems, all focused on maximizing extraction. The move towards pre-ground coffee sacrifices this control, potentially compromising the quality of the final beverage.