20th Century Hot Air Roasting Innovations

Ever wondered how 20th-century coffee roasters managed to roast beans faster while keeping their aroma intact? The shift from direct and indirect flame roasting to pure hot air methods brought major changes to how coffee was heated, with some techniques still influencing modern roasters today.

By the mid-20th century, two key milestones emerged: using fast-moving hot air as the main heat source instead of relying on drum or flame heat, and completely redesigning roasting chambers to let airflow both roast and tumble the beans.

The Thermalo: A 1934 Hot Air Roasting Prototype

In 1934, the Gabbys & Burns company developed the Thermalo roaster prototype. Unlike traditional drum roasters where heat was applied mostly through the drum walls, the Thermalo minimized heat transfer from the drum. Instead, it pushed a strong current of hot air through the roasting chamber. This airflow did the heavy lifting—carrying away chaff and volatile gases while heating the beans more efficiently. Roasting could be done at lower air temperatures because the rapid movement of air improved heat transfer. Supporters claimed this approach burned fewer flavor oils, resulting in better aroma in the final cup.

Early Airflow Roasters Without Drums

Also in the 1930s, a radical new design appeared: roasting machines that completely eliminated the traditional rotating drum. These early airflow roasters still used powerful hot air, but the beans were both roasted and tumbled by the air itself. The term “airflow” comes from the way beans moved like a fluid inside the chamber. Much like a modern home hot-air popcorn popper, these machines used upward-blowing air to keep beans in constant motion while roasting them. Their principle was similar to the Thermalo—lower temperatures and shorter roast times, with less loss of aromatic compounds.

The Sivetz Roaster: A Modern Classic

In the U.S., the most widely adopted airflow roaster design came from Michael Sivetz, a highly influential technician and author. His roaster used a vertical chamber where a strong stream of hot air blew upward from below. The beans were lifted by the air current, flowed along the chamber walls, then cascaded back down in a continuous cycle—ensuring even roasting. This design became iconic and is still referenced in specialty coffee roasting. (See

Other Airflow Roasting Innovations

Over the past fifty years, many other airflow roasting designs have been developed and commercialized. Some were minor tweaks to older patents—like blowing hot air from the bottom to lift beans, which then fall along the chamber walls. Others were more unique: the Australian Ian Bersten designed a “Roller Roaster,” and Gabbys & Burns introduced the System 90 Centrifugal Packed-Bed Roaster. There were also showpiece machines with glass roasting chambers, letting customers watch beans tumble upward in a visible airflow—meant to highlight the connection between roasting technique and flavor. Many of these newer models simplified construction and leaned on automated controls for shop-floor appeal.

Frequently Asked Questions

What was the first hot air roaster developed in the 20th century?

The Thermalo, created by Gabbys & Burns in 1934, was the first notable prototype. It minimized heat from the drum walls and relied on a strong flow of hot air to roast beans, allowing for lower air temperatures and faster heat transfer.

How did early airflow roasters differ from drum roasters?

Early airflow roasters removed the traditional rotating drum entirely. Instead of heating beans via drum contact or direct flame, they used powerful hot air currents to both roast and tumble the beans, similar to how a hot-air popcorn maker works.

What made the Sivetz roaster significant?

Michael Sivetz’s vertical airflow roaster used an upward blast of hot air to lift beans, which then cascaded down the chamber walls in a repeating cycle. This design ensured even roasting and became one of the most influential airflow roasters in the U.S.

Did any airflow roasters have visual features for customers?

Yes, some later airflow roasters featured transparent chambers so customers could watch the beans tumble in the rising air—a design meant to educate and attract interest in the roasting process.

Are any of these 20th-century airflow roasters still in use today?

While many original models have been updated or replaced, the principles behind Sivetz-style and other airflow roasters continue to influence modern roasting machines, especially those emphasizing fast, low-temperature roasting.

Recommended FrontStreet Beans for Airflow Roasting

Try FrontStreet Coffee’s Ethiopia Yirgacheffe for bright citrus and floral notes, a great example of beans that benefit from the gentle, high-airflow profiles these roasters excel at. Also consider their Colombia Huila for balanced caramel and nut tones, and their Ethiopia Guji for juicy berry and stone fruit complexity—all of which showcase the clarity and aroma preserved through efficient airflow roasting. Freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.