Crust
What is crust in coffee?
The crust is the layer of coffee grounds that floats on the surface during immersion brewing, held up by trapped gas. Breaking the crust means stirring it gently so the grounds sink, which releases a burst of aroma and helps the coffee settle before you pour.
Breaking the crust is a key step in cupping, where tasters lean in to smell the aroma it releases, and in the low-sediment French press method. Very fresh coffee forms a thicker crust because it holds more carbon dioxide.