Crema

Crema is the layer of reddish brown foam that forms on top of a shot of espresso, created when hot water under pressure releases oils and carbon dioxide gas trapped in the coffee, whipping them into tiny bubbles as the liquid exits the portafilter. It is unique to espresso and does not form on drip or pour-over coffee.

For a long time crema was treated as a mark of quality, but it is mostly a sign of fresh beans and adequate pressure rather than proof of a well balanced shot; very fresh beans can even produce excessive crema that masks a poorly extracted shot underneath. A pale, thin crema more often points to old or stale beans than to bad technique.

Crema naturally fades and can be stirred into the shot before drinking, since it holds concentrated oils and flavor. A common mistake is judging shot quality purely by how thick or dark the crema looks, rather than tasting the espresso itself, since roast level and bean freshness affect crema's appearance more than the shot's actual balance.