The Process of Roasing Coffee Beans

Somewhere on the world right now, a person is waking up feeling a bit groggy. Perhaps they’re getting ready to go to work or maybe even to school. Regardless of their situation, this person isn’t feeling that great. They just need one thing to put them in the proper frame of mind to have a good day. That thing: coffee.

Coffee is one of the most popular drinks in the world. Its popularity is evident by the fact that it is among the three largest traded commodities in the world. Originally just a simple drink, coffee has spawned numerous other coffee-based beverages from espresso to cappuccino. Trips to the grocery store will inevitably lead into fumbling around the different blends of gourmet coffee and flavored coffee that is available. Coffee beans are a popular product for coffee lovers that prefer to make their own coffee rather than buy it from coffee chains like Starbucks.

When it comes to converting the green coffee beans into the delicious cup of cappuccino that you enjoy at home while reading the newspaper, the most important stage in the coffee preparation process is roasting. The roasting process will have a profound effect on the flavor of your coffee.

Roasting coffee is one of the best ways to become familiar with all of the different flavors and varieties of coffee that is available throughout the world. The roasting process takes the green coffee bean that has been produced on a coffee plant and changes it so it is nearly ready for consumption. The green coffee bean expands during the roasting process to nearly double its original size. Additionally, the color and density of the coffee bean changes while it undergoes the roasting process.

As the bean absorbs heat during the roasting process, oils will appear on the surface of the bean. In addition, the color of the coffee bean will darken until it is removed from its heat source. The color of the coffee bean will shift from green to yellow, as it absorbs heat. The coffee bean will then change from a yellow color to a light, cinnamon brown to a deep brown. The changing colors of the coffee bean is a great way to measure the roasting process and the degree that you roast the coffee bean will have a great effect on the flavor of the coffee bean.

The roasting process is integral to producing a savory cup of coffee. When roasted, the green coffee bean expands to nearly double its original size, changing in color and density. As the bean absorbs heat, the color shifts to yellow and then to a light “cinnamon” brown then to a dark and oily color. During roasting oils appear on the surface of the bean. The roast will continue to darken until it is removed from the heat source.

At lighter roasts, the bean will exhibit more of its “origin flavor” – the flavors created in the bean by the soil and weather conditions in the location where it was grown. Coffee beans from famous regions like Java, Kenya, Hawaiian Kona, and Jamaican Blue Mountain are usually roasted lightly so their signature characteristics dominate the flavor.

As the beans darken to a deep brown, the origin flavors of the bean are eclipsed by the flavors created by the roasting process itself. At darker roasts, the “roast flavor” is so dominant that it can be difficult to distinguish the origin of the beans used in the roast. These roasts are sold by the degree of roast, ranging from “Light Cinnamon Roast” through “Vienna Roast” to “French Roast” and beyond. Many consider that a “full city” roast is a great roast because it is “not too light” and “not too dark”.

In the 19th century coffee was usually bought in the form of green beans and roasted in a frying pan. This form of roasting requires much skill to do well, and fell out of favor when vacuum sealing of pre-roasted coffee became possible. Unfortunately, because coffee emits CO2 for days after it is roasted, one must allow the coffee to get slightly stale before it can be vacuum sealed. For this reason two technologies have recently been employed: Illy has begun to use pressurized cans and many roasters bag whole beans immediately after roasting in bags with pressure release valves.

Today home roasting is becoming popular again. Computerized drum roasters are available which simplify home roasting, and some home roasters simply roast in an oven or in air popcorn poppers. Once roasted, coffee loses its flavor quickly. Although some prefer to wait 24 hours after roasting to brew the first cup, all agree that it begins to get off-flavors and bitterness about 1-2 weeks after roasting even under ideal conditions like being stored in an airtight container or de-gassing valve bag.


The coffee roasting process consists essentially of cleaning, roasting, cooling, grinding, and packaging 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 belt or 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°C (698 and 1004°F), 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 tumble the green coffee beans in a current of hot combustion gases; the roasters operate in either batch or continuous modes and can be indirect- or direct-fired.

Indirect-fired roasters are roasters in which the burner flame does not contact the coffee beans, although the combustion gases from the burner do contact the beans. Direct-fired roasters contact the beans with the burner flame and the combustion gases. 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 “destoner”. Destoners are air classifiers that remove stones, metal fragments, and other waste not removed during initial screening from the beans.

The destoners pneumatically convey the beans to a hopper, where the beans are stabilized and dried (small amounts of water from quenching exist on the surface of the beans). This stabilization process is called equilibration. Following equilibration, the roasted beans are ground, usually by multi-stage grinders. Some roasted beans are packaged and shipped as whole beans. Finally, the ground coffee is vacuum sealed and shipped.

For gourmet coffee that comes from famous coffee growing regions like Java, Mocha, or Kenya, it is best to create a light roast. The longer that you roast a coffee bean, the more original flavor of the coffee bean is replaced by the flavors created by the roasting process. For high quality gourmet coffee beans that are renowned for their unique flavor, it is best to preserve the original flavor. The natural flavor of coffee beans is largely determined by the soil and weather conditions of where they have grown. As a result, gourmet coffee beans from renowned coffee growing areas should be roasted lightly so their distinct flavor are kept for your enjoyment.


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