Coffee Roasting Process

Coffee Roasting Temperature and Coffee Profiles

This study examines temperature gradients and the relationship between heat in the roasting machine and the temperature of the coffee seed.

The source recommends setting the roaster’s working temperature between 140°C and 165°C. The machine temperature and the coffee-seed temperature are not identical: beans absorb heat progressively from their exterior toward their center.

The rate of temperature change increases after the beans reach the end of the drying phase. During drying, moisture becomes vapor and contributes to heat transfer through both contact and convection.

Heat Transfer and Coffee Density

Heat transfer into a coffee seed depends partly on its density. Denser beans generally resist temperature changes differently and may develop more evenly during roasting.

The article gives a typical green-coffee density range of approximately 0.64–0.72 g/mL and describes values above 0.68 g/mL as high density. It associates density with varietal, growing conditions, altitude, soil, water, sunlight, and processing method.

The Maillard reaction—the heat-driven interaction of amino acids and sugars—is identified as an important part of aroma, flavor, browning, and roast development.

Moisture and Batch Consistency

The temperature development of coffee seeds is influenced especially by:

1. Moisture: The article recommends green-coffee moisture between 10% and 12%, with a consistent moisture level throughout the batch.
2. Density: Beans of similar density tend to respond to heat more uniformly, supporting more consistent roast development.

Sorting a batch for relatively consistent moisture, density, and size can therefore improve roasting uniformity.

Roasting Curves

A roasting curve tracks changes in coffee temperature over time. The source discusses a curve for naturally processed Caturra and Red Catuai coffee and notes that the roaster’s heat source and heat distribution affect its performance.

Cooling is the final stage shown on the curve. Rapid, controlled cooling limits continued roast development after the beans leave the roasting chamber.

Sample Roasting

A sample roast uses a representative portion of green coffee to evaluate its quality and sensory characteristics. The source describes samples of approximately 250–300 grams.

For general evaluation, it recommends a relatively light City-style roast, stated as roughly 75–85 on the Agtron scale. A lighter roast can preserve subtle characteristics for assessment. Longer or darker roasting may reduce some delicate flavors while increasing caramelized, chocolate-like notes and lowering perceived acidity.

Customized sample roasts can also test how a coffee performs at a requested profile, such as Full City, and compare changes in aroma, body, flavor, and balance.