Coffee roasting is a fascinating and almost magical operation where green coffee beans transform into aromatic, flavorful roasted coffee beans.

While it may seem relatively basic (heat + time), roasting coffee beans is a scientific and artistic procedure; a number of complex chemical reactions happen throughout the process that result in the coffee's flavor profile and aroma.

The Maillard Reaction

Named after the French chemist Louis Camille Maillard, the Maillard Reaction occurs between reducing sugars and amino acids once the roaster reaches between 280-330°F. As the beans heat up, they lose moisture and begin to brown, creating a range of flavor compounds that contribute to the rich, caramel-like notes in roasted coffee.

Caramelization

Caramelization takes place between the drying and “first crack” stages of roasting and after the Maillard Reaction. “Caramelization” refers to the sugars inside the coffee bean being released after being roasted at temperatures between 325-392°F. This process produces more complex flavors and deepens the color of the
roast; it also develops the sweetness and the characteristic flavors associated with medium to dark roasts.

Changes in Organic Acids

The levels and types of organic acids in coffee change significantly throughout the coffee roasting process.

Here are a few of the main acid types:
Chlorogenic Acids: These are the most prominent organic acids in green coffee beans. During roasting, chlorogenic acids degrade and transform into various other compounds. This breakdown is responsible for the reduced acidity in roasted coffee compared to green coffee.

Quinic Acid: As chlorogenic acids break down, they form quinic acid. The longer green coffee beans are roasted, the more quinic acid they produce. Quinic acid is often associated with coffee's bitter and astringent notes. The longer brewed coffee is left at a high temperature, the more sour it will taste due to the presence of quinic acid.

Citric Acid: Citric acid levels generally decrease during roasting. This acid contributes to coffee's bright, tangy flavors, which become less pronounced in the final roasted product. Light roasts contain more citric acid, and dark roasts tend to include a lot less.

Acetic Acid: Acetic acid forms as sucrose levels are reduced in the beans during roasting. It is most noticeable in light roasts but steadily dissipates the more the beans are roasted.

Check out our coffee roaster (it’s almost 100 years old) and how we roast our beans!