First crack in one of two distinct heat-induced pyrolytic reactions in coffee. It is distinguished by a cracking or popping sound in the coffee, and occurs between 390 and 410 degrees Fahrenheit in most coffee roasters. It has a sound more similar to the popping of popcorn, whereas the Second Crack that occurs around 440 to 450 Fahrenheit has a more shallow, rapid sound, like the snapping of Rice Krispies cereal in milk! First crack involves a rapid expansion of the coffee seed, and marks the point where water and carbon dioxide fracture, leading to the liberation of moisture from the coffee in the form of steam. First crack opens the crease in the bean enough to release remaining silver skin, or chaff. First crack is a clue to the roaster-operator about the roast level, and it’s termination generally marks the first stage (City Roast) where coffee is acceptably dark enough to enjoy.