Second Crack is the second audible clue the roaster-operator receives about the degree-of-roast, following First Crack. Whereas First Crack sounds a bit like popcorn popping, Second Crack has a faster, shallower patter, much like Rice Crispies in milk, electrical sparking, a snapping sound. Second crack is a further stage of the pyrolytic conversion of compounds in coffee and occurs around 440 to 450 degrees Fahrenheit. The 2nd crack is a physical fracturing of the cellular matrix of the coffee, and results in an eventual migration of oils to the outside of the bean, as they are freed from their chambers within the coffee. When second crack is volatile, it can blow small discs off the coffee bean.