The process of coffee roasting is a science that requires more precision than many people realize. Depending on the flavor profile you’re looking for, you may find it beneficial to control the time it takes for your coffee to reach the first crack.
When I first started roasting my own coffee, I went into it completely blind. My roasts were in no way uniform, with some beans dark and others still very light. As I improved, I got better at making more uniform roasts. I did this by roasting at a lower temperature to delay the first crack.
When I roast at home, I usually do so on a cast iron skillet on a gas stove, so it’s easy to control the temperature. Instead of putting the temperature on high, I put it on medium or even low. It takes much longer for the beans to start changing color, but once they do, it is much more uniform, and they don’t get so hot that they cook each other.
I have found that delaying the first crack is good for any roast, though it is better for light and medium roasts. For these roasts, it is more important to retain the unique flavors of the beans, as they’re more apparent once brewed. When going for dark roast, though, I usually roast them at a higher temperature. A faster roast results in a stronger and bolder flavor.
Another noticeable difference in the beans when delaying the first crack is the uniformity of the color. Below, you can clearly see that the slow-roasted batch (left) is a consistent color, while the quicker, higher-heat batch (right) is a mess of dark and light beans. This is the clearest example of the benefits of delaying the first crack.
When doing a slow roast, it’s important not to get impatient and turn the heat too high. If you are using a cast iron skillet, the pan itself retains a lot of heat, which makes it harder to cool down. Typically, I have the heat higher at the very beginning of the roast, and I turn it down once I see the first color change on the beans. I may turn the heat up a little around the start of the second crack, but it isn’t necessary. I’ve had huge successes in drawing out a roast at the same temperature for the whole time.
This difference drastically affects the taste of the coffee. Getting a uniform roast on a cast iron skillet is hard, but it’s very important to the taste of the coffee. A uniform roast has a smooth and stable flavor. The flavors of the roast are clear. A batch of beans with a variety of roast levels will not have the same smooth taste; it will still be delicious, but if you want your roast to be perfect, you want a uniform roast.
As I mentioned above, delaying the first crack is best for light and medium roasts. When I want a dark roast, the uniformity early-on in the roasting process is less important, as they will all darken to the same level after the second crack. The important part in a dark roast is, of course, not over-roasting them, which is easy to do once the beans get hot enough. To prevent this, I suggest turning down the heat once the second crack begins. As the beans retain a lot of their heat, this will not stop the beans from roasting but will keep their heat from growing out of control.