The transformation of raw coffee berries into the popular drink proffered by wholesale coffee roasters involves a process of many stages. First the bright red berries are hand-picked in the field, and then machine-sorted according to color and ripeness. The berries are run through a machine which strips off the sweet flesh and leaves the light brown seed, now called the coffee bean. The beans are then fermented in water to take off the mucilage, a slimy layer which adheres to the beans. At the end of the fermentation process the beans are then washed well and then dried and sorted, and shipped in bulk sacks to the country of destination.
The beans are received by the wholesale coffee roaster, whose job requires high skill and experience. If the coffee is to be decaffeinated, the green beans are processed by soaking and steaming, then placed in solvents which dissolve the oils containing caffeine. Although the natural flavor of the coffee beans is determined by such variables as the soil, climate, and altitude at which the coffee was grown, it is the process of roasting which most influences how the beverage will taste in the end.
Roasting transforms the beans both chemically and physically. The beans lose weight as the remaining moisture within them is lost, and they also increase in volume, becoming less dense. How dense the coffee beans are influences how strong the coffee drink will taste. Different varieties of coffee beans have different moisture contents and different densities, and therefore they require different roasting temperatures and times. Normally roasting takes place at about 392 degrees Fahrenheit (200 degrees Celsius). This intense heat caramelizes the coffee beans, converting the starches inside the beans to simple sugars which turn brown, thus changing the beans' color. As the roasting proceeds the sucrose is broken down and can disappear altogether in longer, darker roasts. During the roasting process the aromatic oils, caffeine content, and acids weaken, which changes the flavor. At slightly higher temperatures (400 degrees Fahrenheit = 205 degrees Celsius) other oils which affect the flavor are formed. The principle one of these is caffeol, which is primarily responsible for the flavor and aroma of the coffee.
The roasted beans are labeled according to color: very dark, dark, medium-dark, medium, medium-light, or light. This determination can be made by humans, or else by illuminating the beans and measuring the reflected light with a light meter known as a spectroscope. Use of this device assures quality and uniformity in the final product. Generally speaking, the darker the roast the smoother the beverage because there is less fiber content, less aromatic acid and oil content, and more sugar in the best coffee bean. On the other hand, the lighter the roast the more caffeine and aromatic oil content is left in the roasted bean, which results in a slightly bitter flavor. Usually North Americans prefer the sweeter, smoother taste of dark roasts whereas Latin Americans prefer the bitter flavor of light roasts. The roasted beans may have chaff left from the outside layer of the beans which must be removed by blowing air over the beans; however a small amount of chaff is left on dark roasted beans in order to soak up the oils from the beans.