NOT ALL HEAT IS EQUAL: How Roasters Transfer Energy to Coffee
From early stage of pan roasting coffee in Ethiopia to industrial fluid bed roasting today, roasting coffee became more and more technical and scientific based models. The 3 types of energy transfers have been studied by the big industrial players .
– Conduction – transfer energy by contact through material to bean or bean to bean
– Convection – transfer from air or liquid to coffee bean
– Radiation – transfer through electromagnetic waves (IR)
All the 3 types coexist in a roasting machine and the trend is to maximize convection, but drum geometry, drum speed and air fan allow to find the best transfer for a specific roasting curve.
About roast curves, we often overlook the deeper physics: how heat is transferred inside a coffee roasting machine. Whether you’re using wood fire or infrared, each heating method favors different modes of energy transfer — and that directly shapes flavor, development, and consistency.
Main heating sources in roasting systems:
– Wood
– Natural Gas
– LPG
– Diesel
– Electricity
– Induction
– Infrared (IR)
– Hybrid systems
Scientific Insight
Each heat source privileges certain thermal pathways:
* Convection heats the air — ideal for mass transfer and even development.
* Radiation delivers energy via waves — more aggressive, good for caramelization but risky for scorching.
* Conduction works through physical contact — precise but slower, seen in electric and some hybrid systems.
A natural gas burner in a drum roaster transfers energy mostly via hot air circulation and flame radiation, while an electric roaster will slowly conduct heat through metal surfaces.
Looking Ahead
As energy prices rise and sustainability becomes imperative, we may see more:
* Induction systems with electromagnetic control
* Recirculated hot-air convection roasters
* AI-based control systems that dynamically balance radiation, convection, and conduction
* Electrified roasters powered by solar or green grids
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