What is the metric used to determine the quality of espresso?

The thickness of the crema is a critical metric for evaluating the quality of espresso because it serves as a visual and sensory indicator of the espresso's richness and extraction quality. Crema is the golden, frothy layer that forms on the surface of freshly brewed espresso. Its presence and thickness are essential indicators of the extraction process and the freshness of the coffee beans used. A thick crema suggests that the espresso has been well-extracted, indicating an optimal balance of oils, compounds, and gases that contribute to flavor and aroma.

While aroma intensity, bean origin, and temperature are important factors in determining the overall experience and flavor profile of espresso, they don't directly reflect the technical aspects of the espresso shot itself as strongly as crema thickness does. Aroma intensity contributes to the sensory experience, and bean origin can influence flavor notes, but crema serves as a tactile and visual cue that helps baristas and coffee enthusiasts immediately assess the quality of their brew. Similarly, temperature can affect the extraction process, but it is the crema that ultimately ties together the visual, aromatic, and textural qualities expected from a high-quality espresso.