We asked one of our roasters, Jacob, to explain what we hear every time a fresh batch of roasted beans in dropped into the cooling tray in our roasterie:
Coffee is much like corn in that when you apply heat it pops or “cracks.” Coffee, however, is different in that it has two distinct times in which it cracks: “first” and “second” crack, as we like to refer to them. From the drop of the beans into the roaster, up until the first crack the coffee bean is basically receiving energy or heat. It eventually gets to a point where it cannot take any more and the cell structure actually begins to break or crack. That is the audible sound that one hears when close to the roaster. In between the first crack and the second crack is generally where the flavor development happens. Essentially, as heat continues to be applied it releases or sets free the volatile flavor oils that we know as the coffee flavor. Also, this is where the browning and caramelization occurs to help create that nutty flavor and color that is coffee. However, like all things, this period must come to an end and it is generally denoted by the second crack: what you are hearing on the video. This second crack does not mean the same thing for all roasters, particular roasts, or particular coffees. Roasting is a craft and depending on what you are trying to accomplish or what you might deem as correct, a roaster might drop the beans into the cooling tray well before the second crack or far beyond it. This is what makes coffee roasting and experimenting with new beans and blends such an interesting job.