The Coffee Roasting Process
Burlap bags of green coffee beans, weighing 60-70 kgs are loaded into the storage hopper, directly above our roaster. Once the roaster has reached proper temperature, the green beans are emptied into the roaster drum and continuiously rotate for approximately 9-12 minutes, depending on style of roast and size of roast; full batch or half batch, etc. Our (90 kg capacity) roaster was built by Probat of Emmerich, Germany, the largest manufacturer of commercial coffee roasters in the world. The rotating drum is heated by natural gas, directly below the drum. This insures that each batch of coffee roasted is evenly roasted, from the first moment the coffee is dropped into the roaster until the coffee is done.
Those who roast coffee often prefer to follow a "recipe" or "roast profile" to highlight certain flavor characteristics. Any number of factors may help a person determine the best profile to use, such as the coffee's origin, varietal, processing method or desired flavor characteristics. A roast profile can be presented as a graph showing time on one axis and temperature on the other, which can be recorded manually or using computer software and data loggers linked to temperature probes inside various parts of the roaster.
Indirect-fired roasters are roasters in which the burner flame does not contact the coffee beans, although the combustion gases from the burner do contact the beans. Direct-fired roasters contact the beans with the burner flame and the combustion gases. At the end of the roasting cycle, the roasted beans are cooled using a vacuum system. Roasted coffee beans are also cooled using fine water mist, which is known as "quenching" and is considered inferior to air cooling as the water soaks the fresh beans with moisture and oxygen particles making it stale almost instantly. Following roasting, the beans are cooled and stabilized. This stabilization process is called degassing. Following degassing, the roasted beans are packaged, usually in light-resistant foil bags fitted with small one-way valves to allow gasses to escape while protecting the beans from moisture and oxygen.