What do you know about roasting coffee beans?
Well, you probably know that roasting causes green coffee beans to expand and change in color, smell and density (and, of course, it provides that characteristic “roasted” flavor). You probably also know that depending on the degree of roast, different flavor characteristics in the bean will be highlighted.
But although coffee blends may be named by their roast (such as “City Roast” or “French Roast”), did you know the roast signifies science more than romance or place? It is actually a degree that refers to internal bean temperature at the apex of roasting.
Most roasters utilize large drums which tumble the beans in a highly-controlled, heated environment, roasting the beans anywhere from 3 to 30 minutes at temperatures ranging from 240 to 275° C. Most people who roast coffee work by sight. They watch as the color of the bean shifts from green to yellow and then to darker and darker shades of brown until oils begin to appear. They also factor in smell and sound to determine the degree of roast. Coffee beans will reach two thresholds of temperature which are called “cracks.” (These cracks sound like corn kernels popping very quietly).
The first crack occurs at 205-207°C and signifies the beginning of a light roast. A second crack occurs at 224-227°C and signifies a medium roast. Anything beyond the second crack is a dark roast. The presence of caffeine decreases the longer a coffee is heated, so contrary to popular opinion, lighter roasts actually have more caffeine content than darker ones. Likewise, the longer a coffee is heated, the more the flavor of roasting will overtake the flavors of the beans’ origin. Thus, coffees known for the region they come from (such as Java, Kenya, or Hawaii) are almost always roasted lightly to allow the flavors of origin to come through.