The Coffee Roasting Process and Its Impact on Aroma and Appearance

Drying Phase
The drying phase is crucial, as green coffee beans contain about 8–12% moisture. This stage, lasting 4–8 minutes, reduces moisture and prepares the beans for subsequent chemical reactions. During this time, beans change color from green to yellow and lose mass and density [1].
Browning/Maillard Reaction
At temperatures between 180°C and 250°C, the Maillard reaction occurs, where sugars and amino acids react to form hundreds of new compounds This stage gives coffee its color and much of its aroma, turning beans from yellow to light brown [2]. The “first crack,” a popping sound, signals the transition to a light roast and is a critical decision point for roasters [1].
Development Phase
After the first crack, beans continue to roast and develop more intense flavors. The duration of this phase determines whether the beans become a medium or dark roast. A “second crack” at higher temperatures indicates a very dark roast, with oils beginning to appear on the surface. [1] [3].
Cooling
Once the desired roast level is achieved, the beans are rapidly cooled to halt the roasting process and preserve their flavor and aroma [2].

Roast Level	Appearance	Aroma Characteristics
Light Roast	Light brown, dry surface	Bright, floral, fruity, pronounced acidity; retains more of the bean's original character and origin notes
Medium Roast	Medium brown, dry or slight sheen	Balanced aroma; sweeter, caramel, nutty, chocolatey notes; moderate acidity and body
Dark Roast	Dark brown to almost black, oily	Bold, smoky, bittersweet, with reduced acidity; original bean flavors are muted, replaced by roast-driven aromas

Light Roasts
Light roasts preserve most of the original flavors and aromas, often described as floral, fruity, or earthy. The beans are light brown with a dry surface, a complex aroma, and higher acidity. There are several types of light roasts, including Light City, Half City, and Cinnamon. These names vary depending on the region and roasting traditions, but all indicate a lighter roast level that stops at or just after the first crack during the roasting process [4] [5].
Medium Roasts
Medium roasts develop a richer, sweeter aroma with notes of caramel and chocolate. The acidity is balanced, and the body is fuller. Beans may appear slightly shiny as oils begin to surface. This stage ends at the second crack [4] [5].
Dark Roasts
Dark roasts are dark brown to almost black and usually shiny due to surface oils. The aroma becomes strong, smoky, and bittersweet, with original bean flavors largely replaced by those from the roasting process. Acidity is greatly reduced, and the body is heavier [4].

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