Coffee Roasting Process

How do you get the rich color of coffee beans and their characteristic flavor? It's the typical coffee roasting process that transforms the green colored beans to dark brown in color. The composition of raw beans and roasted ones is the same, except the taste. Coffee beans are roasted at an industrial scale and there are different gradients of roasting that renders texture and flavor to the final product. The process of roasting coffee beans is elaborated in the next segment.

How to Roast Coffee Beans

So how to roast coffee beans? The degree of roasting is determined by the color of the beans. With increase in temperature and time, the color will change from green to yellow and finally to brown. In the conventional method, the beans 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. The process is accentuated by the supply of more amount of gas. In fluidized bed roasting or hot air roasting, hot gas is supplied from below the machine and the beans are subjected to gas at a high speed. The roasting process is extremely fast and is controlled in the machine. This leads to high quality products and the beans are of superior grade than those roasted by conventional technique. The basic process remains the same and the volume and density of the roasted beans are increased by 40%.

• Before roasting the beans, they are dried and sorted out. The beans are transferred to a hopper, or sorting machine, that removes debris and leaves from the coffee beans. The fresh green beans are then collected for roasting.
• The roasting machine has a heat source fitted with a barrel on top. The beans are kept over the barrel, that keeps on rotating for uniform roast. The temperature is raised to 350 °F and 550 °F so that the color changes.
• The entire process will take maximum 30 minutes for deep roasts. The four stages of roasting are, light (cinnamon roast), medium (American roast, city roast), full (Viennese roast, continental roast) and double (French roast, New Orleans roast) roast. The roasting process is further accompanied by the cracking sound of the beans.
• The first crack develops when the beans turn yellow in color. If you observe the beans throughout the process, you will find out that the cracks grow 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 370 °F. The beans expand and the crack extends from the center to the ends. Some chaff is also released from the beans.
• The brown stage is marked after 9 minutes, and the temperature is nearly to 400 °F. In this stage the crack appears like a groove and after one minute you will hear popping sounds, that marks 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 the coffee beans have cleared the first crack and beans acquire a wood like texture, is known as City+ roasts. Full City roasted beans have richer color with second cracks in them. Other grades of roasted coffee beans are Full City + Vienna stage (light French roast), full French roast and fully carbonized. The beans are packed or ground to make commercial coffee powder.

If the basics are clear, then you can roast fresh coffee beans at home as well. The equipment, or a hot air roaster, can be purchased from departmental stores and you can proceed after reading the instructions for operating it. And then, enjoy the rich aroma of coffee from freshly roasted beans.