yourcoffeeguru:

 Roasting Coffee

Roasting transforms green coffee into the aromatic brown beans that we purchase,  either whole or already ground, in our favorite stores. Most roasting machines  maintain a temperature of about 550 degrees Fahrenheit.  The beans are kept  moving throughout the entire process to keep them from burning and when they  reach an internal temperature of about 400 degrees, they begin to turn brown and  the caffeol, or oil, locked inside the beans begins to emerge.      

This process, called pyrolysis is at the heart of roasting.  It is what produces the  flavor and aroma of the coffee we drink.  When the beans are removed from the  roaster, they are immediately cooled either by air or water. Roasting is generally  performed in the importing countries because freshly roasted beans must reach  the consumer as quickly as possible.

reference: http://www.ncausa.org/i4a/pages/index.cfm?pageid=69