Roasting

Main articles: Coffee processing and Coffee roasting

Roasted coffee beans

Coffee berries and their seeds undergo several processes before they become the familiar roasted coffee. First, coffee berries are picked, generally by hand. Then they are sorted by ripeness and color and 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, which generates massive amounts of highly polluted coffee wastewater. Finally, the seeds are dried; the best, but least utilized method of drying coffee is by using drying tables. In this method the pulped and fermented coffee is spread thinly on raised beds, which allows the air to pass on all sides of the coffee. The coffee is then mixed by hand. and the drying that takes place is more uniform, and fermentation is less likely. Most coffee from Africa is dried in this manner and certain coffee farms around the world are starting to utilize this traditional method as well. Next, the coffee is sorted, and labeled as green coffee. Another way to let the coffee beans dry is to let them sit on a cement patio and rake over them in the sunlight. Some companies use cylinders to pump in heated air to dry the coffee beans, though this is generally in places where the humidity is too high to correctly get the moisture out.^[46]

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.^[47] 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 and 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, though different varieties of beans differ in moisture and density and therefore roast at different rates.^[48] 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.^[49] 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, other oils start to develop.^[48] One of these oils is caffeol, created at about 200°C, which is largely responsible for coffee's aroma and flavor.^[17]

Depending on the color of the roasted beans as perceived by the human eye, they will be labeled as light, medium light, medium, medium dark, dark, or very dark. A more accurate method of discerning the degree of roast involves measuring the reflected light from roasted beans illuminated with a light source in the near infrared spectrum. This elaborate light meter uses a process known as spectroscopy to return a number that consistently indicates the roasted coffee’s relative degree of roast or flavor development. Such devices are routinely used for quality assurance by coffee-roasting businesses.

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 otherwise destroyed by longer roasting times.^[50] A small amount of chaff is produced during roasting from the skin left on the bean after processing.^[51] 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.^[48] 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.^[17] Decaffeination is often done by processing companies, and the extracted caffeine is usually sold to the pharmaceutical industry.^[17]