Roasting Near the Market
Coffee is usually roasted close to where it will be consumed, largely because green coffee is far more stable than roasted coffee and the flavour of roasted beans is at its best within a relatively short window. Roasting methods differ, but the machines most commonly discussed are drum roasters and hot-air, or fluid-bed, roasters, with tangential and centrifugal systems occupying more specialized industrial territory.
Drum Roasters
Invented around the beginning of the twentieth century, drum roasters remain especially popular among craft roasters because they support slower and more deliberate roast development. A metal drum rotates above a flame, keeping the beans in motion so that heat is applied more evenly throughout the batch.
The operator can usually control both the gas flame and the airflow through the drum, which means they can shape not only how much heat is available but also how quickly that heat is transferred into the coffee. These machines range widely in size, with the largest commercial versions capable of roasting roughly five hundred kilograms in a single batch.
Fluid-Bed Roasters
Developed by Michael Sivetz in the 1970s, fluid-bed roasters suspend and heat the beans using jets of hot air. Because airflow is doing most of the work, heat transfer is rapid and roast times are typically much shorter than in a drum roaster.
That faster transfer often causes the beans to expand slightly more, but it also means the process is less associated with the slower flavour-building style preferred by many craft roasters. It is efficient, fast, and technically interesting, though it produces a different roasting rhythm from a traditional drum machine.
Tangential Roasters
Tangential roasters, developed by Probat, resemble large drum roasters but include internal shovels that move the coffee more assertively during heating. This improves mixing and helps larger batches roast more evenly without relying solely on the motion of the drum.
Their total capacity is not dramatically beyond that of the largest drum roasters, but they can operate at faster roasting speeds while still handling substantial commercial volumes.
Centrifugal Roasters
Centrifugal roasters are designed for very large volumes and extremely fast production. Coffee is placed in a large inverted cone that spins, carrying the beans upward along the walls before throwing them back toward the center, where the cycle repeats under intense heat.
Machines of this kind can complete a roast in as little as ninety seconds. That speed minimizes weight loss and can increase extractable yield, which is useful in industrial contexts such as instant coffee production, but it is not a method designed to pursue the most nuanced or expressive cup quality.