The typical coffee roasting process provides the rich dark brown color and characteristic flavor to coffee beans. It transforms the original green-colored beans into brown-colored ones. The composition of both, the raw and the roasted beans is the same, with the only difference being in their tastes. Coffee beans are roasted at an industrial scale and there are different gradients of roasting that render the characteristic texture and flavor to the final product. Given below is the process.
How to Roast Coffee Beans
The degree of roasting for coffee beans is determined by their color. With increase in temperature and time, their color changes from green to yellow, and finally to brown. In the conventional method, they are placed in a rotating drum that is supplied with gas. The gas is heated to 450 °F for deep roasting. The process lasts for ten to twelve minutes. It is accentuated by the supply of more gas.
In fluidized bed roasting or hot air roasting, hot gas is supplied from below the machine, and the beans are subjected to the gas at a high speed. The process is extremely fast, and is controlled in the machine. This leads to high quality products; the beans are of superior grade as compared to those roasted by conventional techniques. The basic process remains the same, but the volume and density of the roasted beans is increased by 40%.
- Before subjecting the beans to this process, they are dried and sorted out. Then, they are transferred to a hopper or sorting machine that removes the debris and leaves from them. The fresh green beans are then collected.
- The roasting machine has a heat source fitted with a barrel on top of it. The beans are kept over the barrel, which keeps rotating for uniform roasting. The temperature is raised to 350 °F and then 550 °F so that their color changes.
- The entire process takes a maximum of 30 minutes for deep roasts. The four stages of this process are, light (cinnamon roast), medium (American roast, city roast), full (Viennese roast, continental roast), and double (French roast, New Orleans roast) roast. The process is also further accompanied by the cracking of the beans.
- The first crack develops when the beans turn yellow in color. It grows deeper and deeper when the color changes from yellow to tan and then to brown.
- The light brown stage is attained after a maximum period of 8 minutes, when the temperature is at 370 °F. The beans expand, and the crack extends from the center to the ends. Some chaff is also released from them.
- The brown stage is marked after 9 minutes, when the temperature is nearly 400 °F. In this stage, the crack appears like a groove, and after one minute you can hear popping sounds, which means that the beans have been lightly roasted.
The beans are either taken out from the roaster or are roasted further to achieve the desired degree of darkness. When they have cleared the first crack stage and acquired a wood-like texture, the grade is known as City+ roasts. Full City roasted beans have a richer color with the second cracks in them. Other grades are Full City + Vienna stage (light French roast), full French roast, and fully carbonized. The beans are then packed or ground to make commercial coffee powder.
Once you get a hang of the basic process, you can roast fresh coffee beans at home as well. The required equipment (hot air roaster) can be purchased from any departmental store. The coffee that is prepared from freshly-roasted coffee beans tastes delicious.