Coffee roasting: general concepts and heat transfer

Have you ever wondered how the coffee we drink every day gets its unique flavor and aroma? The answer lies in the roasting process, an essential step in transforming the green bean into an aromatic and flavorful beverage. Coffee roasting is the process of applying heat to green beans, promoting chemical and physical changes that result in the flavor, aroma and texture we value in a cup of coffee. This heat is transferred in three main ways: conduction, convection and radiation.

Conduction: direct contact heat

Conduction is the type of heat transfer that occurs through direct contact. A good example is when we hold a hot spoon; the heat passes directly from the spoon to our hand. In roasting, something similar happens when the heat from the machine’s drum is transferred to the bean through direct contact. This type of heat is important so that the heat quickly reaches the center of the bean, promoting effective internal roasting. In the roasting process, conduction needs to be well controlled. If the heat is transferred too quickly, the outside of the bean can burn while the inside remains raw, resulting in an unbalanced flavored coffee. A good roaster adjusts conduction to balance the heating of the entire structure of the bean, ensuring a harmonious development of all flavor and aroma compounds.

Convection: circulation of hot air

Convection is when heat is transferred through the movement of hot air around the beans. This method is common in modern roasters because it allows for more even roasting. Hot air circulates inside the drum and helps to heat the surface of the beans evenly. Convection is essential for precise heat control, especially since many roasters have systems that regulate airflow and internal temperature. This method distributes heat evenly and prevents some parts of the bean from becoming more roasted than others, which could compromise the final flavor.

Radiation: heat emitted

Radiation is a form of heat transfer that occurs without direct contact with the bean, such as when we feel the heat of a campfire without touching the flames. During roasting, the heat emitted by the drum or heated elements reaches the beans and helps caramelize the sugars, bringing a complexity of flavors to the coffee. Although it is only one part of the process, radiation needs to be carefully controlled. Like conduction and convection, radiation requires attention to avoid overheating and burning, which can result in bitter-tasting coffee.

The influence of heat transfer on coffee flavor

These three forms of heat transfer (conduction, convection and radiation) are essential to the roasting process, and each of them directly impacts the final flavor of the coffee. For example, if the heat is applied too quickly and intensely, the coffee can acquire a bitter and burnt flavor. A slower and more gradual roast allows the development of sweet and complex flavors, which make the coffee more pleasant to the palate. The intensity and time of exposure to heat also influence the roast profile – light, medium or dark. In lighter roasts, the time of exposure to heat is shorter, preserving the acidity and fruity notes that are characteristic of lighter beans. In medium roasts, we find a balance between acidity and sweetness, which pleases many consumers because it is more balanced. In dark roasts, where the bean is exposed to a higher temperature for a longer period, the flavors become more intense and the acidity is reduced, which results in a drink with a strong and striking flavor.

SIATEC Brasil in control of coffee roasting

At SIATEC Brasil, each piece of equipment is designed to optimize production, ensuring a uniform roast with maximum flavor. SIATEC roasters have advanced temperature control systems and mechanisms that adjust air flow and drum speed. This allows us to achieve different roasting profiles, respecting the individual characteristics of each type of bean. This allows the roasting to be adjusted to highlight the best qualities of the coffee, providing a rich and differentiated experience for consumers.