What is a drum roaster?

A drum roaster is the most common type of coffee roasting machine, in which beans are loaded into a rotating cylindrical drum and heated through a combination of conduction (contact with the hot drum surface), convection (hot air flowing through the drum), and radiation (heat radiating from the drum walls). The drum's rotation keeps the beans constantly tumbling, ensuring relatively even exposure to heat throughout the roast.

Drum roasters range from small home machines like the Aillio Bullet (capable of batches from 100g to 1kg) through commercial sample roasters to full production machines roasting hundreds of kilograms per batch. The Bullet R1 and R2 are the most widely used home drum roasters in the specialty community, valued for their precise control over power, fan, and drum speed alongside comprehensive data logging through the RoasTime software.

The key variables in drum roasting are charge temperature, heat input (power), airflow (fan speed), drum rotation speed, and batch size. Managing these variables across the three main roast phases - drying, Maillard, and development - is the craft of drum roasting. Drum roasters offer more control and repeatability than simpler roasting methods, which is why they're the preferred choice for roasters developing and refining specific profiles.