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Heat transfer: conduction, convection, radiation

This topic explains the three mechanisms of heat transfer—conduction, convection, and radiation—in coffee roasting, how they interact, and their influence on bean development and flavor outcomes.

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  • Coffee Basics Nerds
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Article 1 of 12 in Roasting Fundamentals/
Heat transfer: conduction, convection, radiation

Conduction (Direct Contact Heat)

  • Definition: Heat transfer by direct contact between hot surfaces and coffee beans.
  • Where it happens: In drum roasters when beans touch the hot drum walls or each other.
  • Effect: Provides steady heating but risks scorching if contact is uneven.
  • Flavor impact: Excess conduction can create burnt, ashy notes.

Convection (Hot Air Flow)

  • Definition: Heat transfer through movement of hot air.
  • Where it happens: Roasting chamber airflow circulates heated air around beans.
  • Effect: Ensures even heat distribution and efficient energy transfer.
  • Flavor impact: Promotes clean, bright flavors; too much airflow may dry beans excessively.

Radiation (Infrared Energy)

  • Definition: Heat transfer via electromagnetic waves (infrared).
  • Where it happens: From hot surfaces (drum walls, burners) radiating energy to beans.
  • Effect: Provides background heating; less controllable than convection.
  • Flavor impact: Contributes to balanced development but can intensify dark roasts if over-applied.

Balance of Heat Transfer

  • Drum roasters: Mix of conduction, convection, and radiation (ratios vary by design).
  • Fluid-bed roasters: Primarily convection-dominant.
  • Infrared roasters: Rely heavily on radiation.

Practical Implications for Roasters

  • Adjust airflow and drum speed to manage convection vs conduction.
  • Use charge temperature and heat application curves to control transfer balance.
  • Monitor bean color, aroma, and rate of rise to ensure even development.

Lasting Importance

Understanding conduction, convection, and radiation is fundamental to controlling roast profiles. Each mechanism shapes bean development differently, and mastering their balance allows roasters to achieve consistent, high-quality, and distinctive flavor outcomes.

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Coffee Basics Nerds

Written by : Coffee Basics Nerds

Expert coffee historians and brewing enthusiasts dedicated to sharing the rich heritage and techniques behind your perfect cup of coffee.

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