Coffee Roasting Process

Coffee drinkers are aware of what they prefer – varietals, roast (light, medium, dark etc.) preferred brewing method (pour over, espresso, French press etc.). However, few are acquainted with the intricacies of the roasting process crucial to determining the final taste and aroma.

Here, we will explore the stages of roasting green coffee, from the green coffee beans to the final product, and explain the significance of color, sound, and temperature throughout the process.

Picture collage of coffee beans at various roast stages in glass roasting chamber
Green beans in roasting chamber by Aurora's Cup Coffee

Start With Green Beans

The roasting process begins with green coffee beans, which are sourced from different regions around the world. The beans are usually stored in large burlap sacks, and they retain their green color until they are roasted.

Appropriately stored, green coffee can be stored for years without harming the bean’s qualities. Green beans do not have the characteristic “coffee smell”, instead they have a smell like cut grass.

Grean beans at drying out roasting phase in roasting chamber by Aurora's Cup Coffee

First Stage

The first stage of roasting is known as the drying phase, which is usually done at a temperature of around 180-200°C. In this stage, the green coffee beans lose their moisture content, which is typically around 10-12%, and turn yellow in color. This stage can take anywhere from 5-10 minutes, depending on the roasting machine and the batch size. During the first stage, roasting coffee smells similar to baking bread or pastry.

Coffee beans at second roasting stage in roasting chamber by Aurora's Cup Coffee

Second Stage

The second stage is the browning phase, where the coffee beans start to develop their characteristic aroma and flavor. The temperature is increased to around 200-220°C, and the beans start to turn brown. This stage is critical in determining the final taste and aroma of the coffee, and the roaster needs to monitor the beans carefully to avoid over or under-roasting. At this stage, the beans start to crack, and the sound of cracking can be heard, which is an important indicator of the roasting progress. The first crack usually occurs at around 200°C, and it sounds like popcorn popping. The “first crack” marks the transition from light to medium roast, and the beans start to develop their acidity and fruity flavors. During the second stage roasting coffee can smell like nuts roasting.

Coffee beans at third roasting stage after first crack in roasting chamber by Aurora's Cup Coffee

Third Stage

The third stage is known as the development phase, where the beans are roasted to their desired level of darkness. The temperature is usually increased to around 220-230°C, and the beans turn darker in color. At this stage, the second crack can be heard, which is more subtle with a “crackling" very reminiscent of a certain crispy rice breakfast cereal This crack marks the transition from medium to dark roast, and the beans start to develop their chocolate and caramel flavors. The third stage can be quite smoky and pungent in odor. In the third stage roasting develops very quickly from medium dark to very dark and oily in a matter of seconds and the roaster needs to carefully monitor the beans to avoid over-roasting or burning them.

Roasted coffee bean after roast process is complete in roasting chamber by Aurora's Cup Coffee

Final Stage

The final stage is known as the cooling phase, where the roasted beans are rapidly cooled to stop the roasting process. This is done to prevent the beans from over-roasting and to preserve their flavor and aroma. The beans are forced-air cooled (sometimes called “quenching”), and then transferred to a vented storage container to rest for a few days.

This resting period allows the beans to release any remaining carbon dioxide and to develop their full flavor and aroma. Resting coffee can produce considerable carbon dioxide which is why coffee bags have a one-way valve on them to let the carbon dioxides out, and the outside oxygen from getting in, and to keep the bags from inflating and potentially bursting.