Commercial Roasting of Coffee Beans.

The roasting process is fundamental to preparing ready to make coffee. When roasted, the green coffee bean expands to nearly double its original size, changing in color, taste, smell and density. Un-roasted beans contain all of coffee’s acids, protein, and caffeine — but none of its taste! It is only roasting that produces the chemical reactions to unlock the characteristic coffee flavor.

Green coffee is more stable than roasted and so the roasting process should be closer to where it will be consumed. This reduces the time in distribution that helps to maximize shelf life. The vast majority of coffee is roasted commercially on a large scale, but some coffee drinkers roast coffee themselves in order to savor the freshness of roasted beans.

The coffee roasting process consists essentially of cleaning, roasting, cooling, grinding, and packaging operations. In larger operations, bags of green coffee beans are hand or machine-opened, dumped into a hopper and screened to remove debris. The green beans are then weighed and transferred by a pneumatic conveyor to storage hoppers. From the storage hoppers, the green beans are conveyed to the roaster. Roasters typically operate at temperatures between 370 and 540 °F (188 and 282 °C), and the beans are roasted for a period of time ranging from a few minutes to about 30 minutes. Roasters are typically horizontal rotating drums that keep tumbling the green coffee beans.

At the end of the roasting cycle, water sprays are used to "quench" the beans. Following roasting, the beans are cooled and run through a "de-stoner". De-stoners are air classifiers that remove stones, fragments, and other waste not removed during initial screening from the beans. Following this the roasted beans are either ground or packaged as whole beans. Roasted whole beans can be considered fresh for up to, but not exceeding one month.