The Roasting Process

Coffee berries and their seeds undergo multi-step processing before they become the roasted coffee with which most Western consumers are familiar. First, coffee berries are picked, generally by hand. Then, the flesh of the berry is removed, usually by machine, and the seeds – usually called beans – are fermented to remove the slimy layer of mucilage still present on the bean. When the fermentation is finished, the beans are washed with large quantities of fresh water to remove the fermentation residue, generating massive amounts of highly polluted coffee wastewater. Finally the seeds are dried and sorted and labeled as green coffee beans.

The next step in the process is the roasting of the green coffee. Coffee is usually sold in a roasted state, and all coffee is roasted before it is consumed. It can be sold roasted by the supplier, or it can be home roasted. The roasting process influences the taste of the beverage by changing the coffee bean both physically and chemically. The bean decreases in weight as moisture is lost but increases in volume, causing it to become less dense. The density of the bean also influences the strength of the coffee and requirements for packaging. The actual roasting begins when the temperature inside the bean reaches 200 °C (392 °F), though different varieties of beans differ in moisture and density and therefore roast at different rates. During roasting, caramelization occurs as intense heat breaks down starches in the bean, changing them to simple sugars that begin to brown, changing the color of the bean.[34] Sucrose is rapidly lost during the roasting process and may disappear entirely in darker roasts. During roasting, aromatic oils, acids, and caffeine weaken, changing the flavor; at 205 °C (400 °F), other oils start to develop.[33] One of these oils is caffeol, created at about 200 °C (392 °F), which is largely responsible for coffee’s aroma and flavor.

Grades of coffee roasting; from left: unroasted (or “green”), light, cinnamon, medium, high, city, full city, French and Italian.Depending on the color of the roasted beans, they will be labeled as light, cinnamon, medium, high, city, full city, French, or Italian roast. Darker roasts are generally smoother, because they have less fiber content and a more sugary flavor. Lighter roasts have more caffeine, resulting in a slight bitterness, and a stronger flavor from aromatic oils and acids destroyed by longer roasting times. A small amount of chaff is produced during roasting from the skin left on the bean after processing. Chaff is usually removed from the beans by air movement, though a small amount is added to dark roast coffees to soak up oils on the beans. Decaffeination may also be part of the processing that coffee seeds undergo. Seeds are decaffeinated when they are still green. Many methods can remove caffeine from coffee, but all involve either soaking beans in hot water or steaming them, then using a solvent to dissolve caffeine-containing oils. Decaffeination is often done by processing companies, and the extracted caffeine is usually sold to the pharmaceutical industry.