Profiling High-Altitude Washed African Geishas & Yirgacheffes on Cast Iron Drums
Detailed roast profile recipes for dense, high-grown specialty lots: charge temperatures, drum speed modulation, and extended drying phase strategies.
The Density Challenge of High-Elevation Coffees
Washed coffees harvested at altitudes above 1,900 meters (such as Ethiopian Yirgacheffe, Guji, and Gesha Village micro-lots) exhibit extremely dense cellular structures with low internal porosity.
Charging these coffees into an overheated drum causes immediate surface tipping and scorches the silver skin, whereas an excessively cool charge leads to stalled development, flat citric acidity, and vegetal grassy off-flavors.
4-Phase Roasting Protocol on RC-Tech CAST-5 & CAST-15
Phase 1: Controlled Charge & Gentle Soak - Charge Temperature: 195°C – 205°C (depending on batch size). - Soak Phase: Keep burner at 20% power for the initial 60 seconds. This allows conductive heat absorption into the core of dense beans before aggressive convection begins. - Turning Point (TP): Target TP at 1:15 to 1:25 at approximately 92°C.
Phase 2: Maximum RoR & Convective Drying - Accelerate burner to 85% immediately post-TP. - Maintain airflow at 45% to prevent surface dehydration while purging early steam exhaust. - Peak RoR target: 22°C/min on 1.5mm ungrounded thermocouple probes.
Phase 3: Smooth Maillard Deceleration - At 155°C (Yellowing transition), step burner down linearly to 60%. - Increase airflow damper to 70% to sweep chaff out into the cyclone and illuminate floral monoterpenes.
Phase 4: Development Ratio (DTR) - Target First Crack at 8:30 – 9:00 at 196°C. - Drop power to 30% right before the first auditory crack, holding RoR steady between 4°C/min and 6°C/min. - Development Time Ratio (DTR): 12.5% to 14.0% for filter roast; drop at 204°C for vibrant bergamot, peach, and black tea notes.
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