The drum in drum roasters is typically made of cast iron and is heated directly by a gas burner underneath, which also heats the air being pulled through the machine by a large exhaust fan.

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Unidentified Speaker — Coffee Roasting Explained [N6BJVM5tvnw]

Evidence Quote

You have underneath here a heat source, typically it's a gas burner... gonna heat the big metal drum typically made of cast iron, but primarily it's gonna heat air.

Source

Coffee Roasting ExplainedJames Hoffmann
Created: 8/13/2026, 9:53:30 AM

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