Temperature Gradients

Coffee Roasting Temperature and Coffee Profiles

The article examines the relationship between heat, roasting-machine temperature, and the temperature of green coffee beans during roasting.

Working temperature

The working temperature is the temperature set on the roasting machine. The article recommends a range of 140°C to 165°C—approximately 284°F to 329°F—and associates this range with Maillard reactions while seeking to limit excess bitterness and acrylamide formation.

It distinguishes the roaster’s working temperature from the temperature reached by the coffee beans. According to the article, bean temperature can be measured when the beans leave the machine.

Temperature gradients and heat transfer

The temperature gradient changes over time as heat moves from the exterior of each bean toward its interior. Even if the roasting machine remains at a constant temperature, such as 160°C, bean temperature continues to change according to the rate of heat transfer and the elapsed roasting time.

The article states that the fastest temperature change occurs after the beans have passed through the drying phase.

Drying phase

The drying phase is the period required for water within the green coffee beans to become vapor. The article explains that this vapor contributes to heat transfer within the roasting system, alongside heat transferred through contact and convection.