Last week we discussed the science of First Crack, and the artistic knack it takes to control your Roast Development, a.k.a. the time between First Crack and when you terminate your roast. Today we touch on the important features of Second Crack.
Second Crack. Not long after the completion of First Crack, your beans will begin to crack a second time. As discussed last week, First Crack happens when the internal moisture of your beans turns to gas and violently escapes. Once that moisture is gone, the roasting energy is absorbed by the cellular structure of the bean and its oily compounds. As that material continues to heat up, structural fracturing occurs in the increasingly brittle beans, giving way for the oils to creep to the surface as bean mass steadily burns away. Ever notice how much less dark roast coffee weighs?
The sound during this stage will be softer and more muted than First Crack, but it can come on quickly and actively. It’s crucial to pay close attention during this stage and have a clear idea of what you’re aiming for because delicate characteristics of your beans are now changing (and arguably deteriorating) at a rapid rate. If you’re aiming for a medium or lighter roast, you should never hear Second Crack, as reaching that point means you have missed the window for that desired roast profile.
Fire Risk. Your cue that Second Crack is imminent will be the increase in smoke. It will start off light and somewhat sweet, but it will thicken quickly. Oils will start releasing from within the bean and collecting on the surface of the bean. In this second, exothermic phase, heat is being generated from the beans themselves and with the increased heat and accumulating oil, fire is a very real threat.
If you’re roasting on a popcorn popper or a similar sort of hacked roaster, we honestly recommend trying to avoid Second Crack altogether. The supercharged beans and their hot oils, mixed with the fact that your roaster has now been running for a significant amount of time, can easily turn your Saturday morning roast into a backyard barbecue.
Stopping the roast. Stopping the roast at the beginning of Second Crack is what we consider to be the narrow target zone for a full city roast, which can yield pleasant and sweet flavor results. But acidity and unique character are dissipating quickly, giving way to the “French” and “Italian” styles, which have their own unique character in their own right.
Beware the Second Crack. Some people prefer their coffee roasted into Second Crack but it’s important to know that if you’re paying top dollar for top shelf green coffee beans, those special flavor features you’re paying for can easily burn away (literally) as you wade into Second Crack.
Carbonizing. This is not an officially acknowledged “stage” in coffee roasting, but it’s very much a real result you can “achieve” by over-roasting. As coffee continues into and even past its second crack, it will continue to darken, release oils, char, and eventually reduce to nothing but carbon. Seriously.
The official Agtron “gourmet” scale used in coffee color analysis (between 100-0) states that at zero the organic matter in the coffee beans has been burned to pure carbon and is no longer drinkable. If your coffee has reached an Agtron of zero you will already have emptied your fire extinguisher.
The main point in all this is to emphasize the importance of well-reasoned roasting. Too light is undrinkable; too dark is undrinkable. Somewhere in between early First Crack and early Second Crack is the magical sweet spot for each coffee, and it’s up to the artisan to hunt that down in a thoughtful, educated and creative pursuit.