Crema

Crema forms during espresso preparation when oils and carbon dioxide from the coffee are emulsified with the water under pressure. When the liquid exits, the pressure is released and a fine-pored, hazelnut to reddish-brown foam forms on the surface.

It depends on freshness, roast, grind and blend. Freshly roasted coffee and a share of Robusta favour a strong crema. On its own, however, it does not reliably indicate taste, and it collapses again after a short time.