An audible popping sound heard during roasting. In coffee, one refers to “first crack” and “second crackAfter First Crack, a roast reaction around 440 to 450 degrees that is distinguished by a snapping sound. Second Crack is the second audible clue the roaster-operator receives about the degree-of-roast, following First Crack. Whereas More,” which come from two different classes of chemical reactions.: An audible popping sound heard during roasting. In coffee, one refers to “first crack” and “second crack,” which come from two different classes of chemical reactions.