Roasting coffee is a method used to transform the chemical and physical properties of green coffee beans into roasted coffee beans.
This roasting process is essential to produce a savory cup of coffee. When the green coffee beans are roasted, the bean nearly doubles its original size while changing in color and density. As the bean absorbs heat, the color shifts to yellow and then to a light "cinnamon" brown before turning a dark and oily color. Roasting causes oils to appear on the surface of the bean. The roast will continue to darken until it is removed from the heat source.
When the beans are at lighter roasts, they will exhibit more of their origin flavors, those flavors that are created in the bean by the soil and weather conditions in the location where it was grown. Regions like Java, Kenya, Hawaiian Kona, and Jamaican Blue Mountain often roast their coffee beans lightly in order to preserve the coffee’s signature characteristics.
When the beans darken to a dark brown, the origin flavors of the beans are overshadowed by the flavors created by the roasting process itself. When the beans are at darker roasts, it is hard to distinguish the origin of the beans used in the roast because the roast flavor is so dominant.
The Coffee Roasting Process
The coffee roasting process consists of cleaning, roasting, cooling, grinding, and packing operations. When larger operations are present, the bags of green coffee beans are either hand or machine-opened, dumped into a hopper, then screened to remove any debris. After this process is done, the green coffee beans are weighed and moved to a storage hopper by either a belt or a pneumatic conveyor. Once the green beans are in the storage hopper, the green beans are conveyed to the roaster. The roasters usually run at temperatures between 370°F and 540°F, and the beans roast in anywhere from a few minutes to about 30 minutes. The roasters that are used to roast the coffee beans are typically horizontal rotating drums that tumble the green coffee beans in a current of hot combustion gases. Other types of roasters use electricity or even heat from wood to operate. The roasters can be operated in batches or in a continuous mode and can be indirectly or directly fired.
Indirectly fired roasters are roasters where the coffee beans do not come in contact with the burner flame, even though the combustion gases from the flame do come in contact with the beans. Directly fired roasters coffee beans come in contact with both the burner flame and the combustion gases. When the roasting cycle is complete, water sprays are used to quench the beans. The beans are then cooled and run through a destoner. Destoners are air classifiers that are used to remove stones, metal fragments, and other waste that was not removed from the initial screening of the beans. The beans are stabilized and dried, leaving small amounts of water on the beans from the quenching. This process of stabilization is called the equilibration. The roasted beans are then either ground by multi-stage grinders or packaged as whole beans. Roasted whole beans are said to be fresh for up to but not exceeding 1 month. Once the coffee beans are ground, they are good for up to 24 hours. Beans that are unroasted boast all of coffee’s acids, protein, and caffeine, but none of its taste. Heat is necessary to spark the chemical reactions that turn carbohydrates and fats into aromatic oils, burn off moisture and carbon dioxide, and alternately break down and build up acids, thereby unlocking the characteristic coffee flavor.
The Different Roasts of Coffee
Roasted coffee beans are like wine: there is no substitute for your personal taste. Light roasted coffees are also known as Cinnamon roast, half city, and New England. These coffee beans are roasted for about seven minutes until the beans pop and double in size. The surface of light roasted beans is dry, and their flavor is light-bodied and somewhat sour, grassy, or snappy.
Medium roasted coffee beans are also known as Full City, American, regular, breakfast, and brown. These coffee beans are roasted for nine to twelve minutes. The surface of medium roasted beans is dry and their flavor is a bit sweeter than light roast with a full body balanced by acid snap, aroma, and complexity.
Dark roasted coffee beans are also known as High, Viennese, Italian Espresso, and Continental. These coffee beans are roasted for twelve to thirteen minutes until the beans begin hissing and popping again and oils rise to the surface. The surface of dark roasted beans is slightly shiny and their flavor is spicy. Complexity is traded for rich chocolate body in dark roasted beans, and the aroma is exchanged for sweetness.
The darkest roasted coffee beans are also known as French. These coffee beans are roasted for fourteen minutes or so when the beans grow quiet and begin to smoke. Having caramelized, the bean sugars begin to carbonize. The surface of these beans is very oily and their flavor is smoky; this darkest of roasts tastes primarily of roasting and not of the inherent flavor of the bean.