Oily Beans (roasted coffee)

After the second crack, the internal cell walls of roasted coffee break down and oils migrate to the bean surface, creating a shiny, oily appearance. Oily beans are a visual marker of dark roast (Agtron below 40). Surface oils are more susceptible to oxidation and rancidity, reducing shelf life and clogging burr grinders. Specialty roasters typically avoid oiling by keeping profiles under second crack. Some espresso blends use light surface oil for crema texture.