If you’re roasting coffee you are certainly familiar with the term First Crack. Here is a quick overview of the basic science of First Crack and how it represents a key moment in managing your roast.
Leading up to First Crack (Drying). In the early stages of your roast, your coffee beans will absorb energy/heat. We can think of this as an endothermic process (the beans are drawing heat inwards). As the coffee beans absorb that heat, the internal moisture will begin to gradually dissipate and the green coffee beans will begin to yellow. This can take up to 5 or more minutes in a commercial drum roaster, much less with small home roasters.
As this chemical process continues, the trapped water continues to expand, turning into gas. When it reaches a critical point where it needs to escape, the beans stop absorbing energy and instead expend it: exothermic.
First Crack. This escaping gas violently cracks open the exterior of the shell of the coffee bean and the resulting, audible First Crack is the theatrical evidence of that transforming activity. What is known as First Crack in roasting is not the first bean crack, but the first short series of cracks indicating the batch has started its action. Marking this moment in roasting is critical to planning and managing your roast!
Roast Development Time (RDT). The time between First Crack and when you terminate your roast is widely referred to as the Roast Development time, or just Development. It is within this window where the individual nuances of your coffee; aromatics, acidity, sweetness, etc. come alive. This window is really where the artistic side of roasting coffee comes into play.
Depending on your roasting equipment, you may or may not have all the control you'd like over the Development stage, but it's helpful to understand the importance of this phase and thoughtfully control as much as you can...and in the form that suits you.
Planning RDT. To plan and execute your Roast Development, it is helpful to think of it as a percentage of time of the total roast cycle from charge to dump. As an example, if you are roasting your coffee for 8 min before it begins first crack and you terminate the roast at 10 min, your Roast Development Time (RDT) is 20%. You will want to plan this percentage before you start roasting. The moment you hit your target percentage is the moment you stop the roast and start quickly cooling your coffee.
There is no hard and fast "rule" for perfectly dialing in your RDT, but something between 15%-25% is a great place to start with a coffee and you’ll quickly get a feel for how this number influences your results.
Keep in mind that once your coffee reaches its exothermic stage and stops absorbing so much energy, it’s easy for roasting to accelerate. You can burn your coffee or end up with a shortened RDT, so you’ll need to dial back the heat for a gentle finish.
Next week, we take up Second Crack…