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Roast Phases (Drying, Browning, Development)

Roast Phases The three distinct stages coffee passes through during roasting: Drying, Browning (Maillard), and Development. Each phase has unique chemical reactions and requires specific temperature and time management. Understanding phases crucial for roast control. Phase 1: Drying Phase Temperature Range From ambient (20-25°C) to approximately 160°C (320°F). First and longest phase by time. Typically 4-8 minutes depending on roast profile and batch size. Water Removal Primary goal: Remove moisture from beans. Green coffee starts at 10-12% moisture. Moisture evaporates as beans heat. Endothermic process (absorbs heat). Beans turn from green to yellow. Color Changes Green → Pale green → Yellow-green → Yellow → Light tan. Grassy smell transitions to bready/hay-like. No significant flavor development yet. Preparing beans for flavor development phases. Energy Dynamics Beans absorb heat without significant temperature rise initially. Moisture evaporation requires energy (latent heat). Bean temperature lags behind drum/air temperature. Patience required - rushing creates defects. Objectives - Remove moisture uniformly throughout bean - Avoid surface scorching (too fast) - Avoid baking (too slow, too low heat) - Prepare bean structure for Maillard reactions - Achieve even heat penetration Common Drying Phase Problems - Tipping: Burning bean tips from excessive heat - Scorching: Surface burning while interior undercooked - Baking: Too slow drying, creates bready/flat flavors - Uneven drying: Inside/outside moisture imbalance Phase 2: Browning Phase (Maillard) Temperature Range Approximately 160°C to 196°C (320-385°F). Browning begins around 160°C, accelerates rapidly. Ends at first crack (196-205°C). Typically 3-5 minutes duration. Chemical Reactions Maillard reactions dominate (amino acids + sugars). Caramelization begins (sugar breakdown). Hundreds of flavor compounds created. Brown color develops (melanoidins). Most critical phase for flavor development. Color Changes Light tan → Tan → Light brown → Medium brown. Browning accelerates exponentially. Color change rate increases dramatically. Aromatic intensity increases. Gas Production CO2 production begins and increases. Pressure builds inside bean. Leading to first crack. Steam continues to escape. Bean volume begins expanding. Flavor Development - Sweet, bready aromas appear (Maillard products) - Nutty, malty notes develop - Caramel sweetness emerges - Acidity structure forms - Origin characteristics begin expressing Rate of Rise (ROR) Should decline steadily through this phase. Declining ROR indicates controlled energy application. Increasing ROR risks running away, lack of control. Target: smooth declining curve. Objectives - Maximize Maillard reaction quality - Develop sweetness and complexity - Prepare beans for first crack - Maintain declining rate of rise - Even heat distribution throughout bean Browning Phase Problems - Flicking/scorching: Surface over-roasting - Underdevelopment: Insufficient time/heat - Baked flavors: Too low heat, too slow - Running away: Excessive heat, losing control Phase 3: Development Phase Temperature Range From first crack start (~196-205°C) to final drop temperature. Temperatures rising to 210-240°C+ depending on desired roast level. Critical decision-making phase. First Crack Audible popping as bean structure fractures. Pressure release from internal CO2 and steam. Beans expand significantly (50-100% volume increase). Marks beginning of development phase. Roast level determination point. Development Time Time spent after first crack begins. Critical for final roast character. Typically 15-25% of total roast time. Light roast: 60-90 seconds development. Medium: 90-150 seconds. Dark: 150-300+ seconds. Development Time Ratio (DTR) Percentage of total roast time spent in development. Formula: (Development Time / Total Roast Time) × 100. Specialty coffee typically targets 15-25% DTR. Higher DTR risks baked flavors. Lower DTR risks underdevelopment. Chemical Reactions - Continued Maillard reactions (diminishing) - Extensive caramelization - Chlorogenic acid breakdown - Organic acid development and loss - Oil migration to surface (dark roasts) - Sugar carbonization (dark roasts) Roast Level Determination Light: Stop shortly after first crack (196-205°C). Medium: Between first and second crack (210-220°C). Medium-dark: Approaching second crack (225-230°C). Dark: Into second crack (235-245°C). Objectives - Achieve target roast level - Develop desired flavor profile - Balance sweetness, acidity, body - Avoid defects (underdevelopment, scorching, tipping) - Maintain bean integrity Development Phase Problems - Underdevelopment: Insufficient development time, grassy/cereal flavors - Baked flavors: Too long at low temperatures - Over-roasting: Too dark, bitter, charred - Second crack timing: Critical decision point Phase Management Heat Application Strategy Drying: Moderate, steady heat application. Browning: Increasing heat but controlled. Development: Careful heat management, often reducing toward end. Energy Balance Exothermic phase begins in development (reactions produce heat). Roaster must compensate by reducing heat input. Failure to adjust leads to "running away." Bean temperature can accelerate uncontrollably. Thermal Momentum Beans store thermal energy. Temperature continues rising even with heat reduction. Must anticipate and reduce heat early. Momentum greatest in development phase. Experienced roasters "steer" with anticipation. Drop Temperature vs Time Both matter for roast level. Same temperature reached quickly = different result than slowly. Development time creates complexity. Temperature alone insufficient metric. Time-temperature-development interaction complex. Roast Profiling Profile Design Planned curve of temperature over time. Each phase has target temperatures and durations. Adjustments for bean density, desired profile, batch size. Profiles reproducible once dialed in. Fast Roast Profile 8-12 minutes total. Higher heat application. Shorter phases. Risks: Scorching, underdevelopment. Benefits: Brightness, acidity preservation. Requires skill to execute well. Slow Roast Profile 15-20+ minutes total. Lower heat application. Extended phases. Risks: Baking, flat flavors. Benefits: Sweetness development, body. Easier control for beginners. Crashed Roast Sudden temperature drop or stall during roast. Usually in drying or browning phase. Creates baked flavors, underdevelopment. Result of inadequate heat application. Common beginner error. Flick Sharp temperature spike during roast. Often from excessive heat application. Creates scorching, uneven development. Visible as burned spots on beans. Avoided through smooth heat application.

Related Notes: - Coffee Terminology MoC