The way in which coffee is roasted can have a profound effect on its taste. Roast too quickly at too high a temperature, and you'll scorch the exterior of the bean. Roast too slowly at too low a temperature, and you'll sap the bean of its of flavor. Over the years, numerous roasting methods have been developed to address these challenges, all with the same objective: To transfer heat to the coffee bean, initiating a series of chemical reactions that prepare it for consumption. Most roasting methods include the following six phases:
- Drying Cycle
This is the first phase of the roasting process, when the temperature of the beans rises to 100 degrees centigrade. Also in this phase, the beans change from a bright green color to a pale yellow.
- First Crack
When the beans reach 160 degrees centigrade, complex chemical reactions begin to occur causing a cracking sound.
- Roast Initiation
The beans swell to 140 - 160% of their initial size. Elements within the beans begin to caramelize, giving the beans their brown color.
In this phase, the audible cracking ceases, but the reactions continue. The time of this silence will depend on the amount of heat applied by the roaster.
- Second Crack
The progressive dehydration of the beans has made them brittle. As a result, more cracking can be heard. It is at this stage that elements in the bean begin to carbonize, producing the burnt characteristics of extremely dark roasts.
- Stopping the Roast
Once the optimal amount of roasting time has elapsed, the beans must be cooled quickly. This is usually accomplished by introducing large amounts of cool air or water.