Drying Phase

Coffee Roasting Temperature and Coffee Profiles

The working temperature is the temperature configured on the roasting machine. The article recommends a range of 140°C to 165°C and relates this range to the Maillard reaction, heat transfer, and the avoidance of excessive bitterness.

During roasting, the temperature gradient changes over time as heat moves from the exterior of each coffee seed toward its interior. Even when the roaster remains at a constant working temperature, the seed temperature continues to rise according to the relationship between heat transfer and time.

The drying phase

The fastest temperature change occurs just after the coffee seed is considered dry. The drying phase is the period required to remove moisture from the seed. As its water becomes vapor inside the roasting system, it contributes to heat transfer through contact and convection.

Moisture and density

The article identifies two important influences on coffee-seed temperature:

1. Moisture: Green coffee should generally contain 10% to 12% moisture, with a consistent moisture level throughout the roasting batch.
2. Density: Denser seeds tend to resist heat-induced change and may support more even roast development.

Coffee-seed density is described as commonly ranging from approximately 0.64 to 0.72 g/mL, with values above 0.68 g/mL treated as high density. The article also discusses relationships among density, altitude, coffee variety, growing conditions, fermentation, and chemical composition.

Roasting curves

A roasting curve records the change in coffee temperature over time. Its shape reflects the drying stage, subsequent roast development, and the final cooling stage. Heat-source performance and heat distribution within the machine also affect the curve.