Roast Defects¶
Roasting Defects Problems during roasting creating negative flavors or appearance. Can ruin excellent green coffee. Result from improper temperature, timing, or technique. Range from subtle quality loss to complete ruin. Require skill and attention to prevent. Scorching Definition Surface burning while interior under-roasted. Dark burn marks on bean surface. Occurs from excessive heat application too early. Creates burnt, charred, harsh flavors. Visible as dark patches on bean. Causes Drum/air temperature too high at start. Charging temperature too high. Excessive heat application in drying phase. Poor heat management. Rushed roasting. Prevention Appropriate charging temperature (180-200°C typical). Moderate initial heat application. Gradual heat increase. Monitor bean temperature closely. Patient drying phase. Detection Visual: Dark burn spots on bean surface. Aroma: Burnt, smoky smell. Taste: Harsh, burnt, acrid flavors. One scorched bean affects multiple cups. Tipping Definition Burning of bean tips/ends. Dark points at bean extremities. Occurs from excessive heat during drying/early browning. Common defect in rushed roasts. Less severe than scorching but still negative. Causes Too much heat too early. High drum temperature at charge. Thin beans or pointed varieties more susceptible. Small beans in mixed batch. Inadequate drum seasoning (new roasters). Prevention Lower charging temperature. Gentler early heat application. Sort bean sizes before roasting. Proper roaster setup. Moderate heat curve. Impact Creates bitter, burnt notes. Reduces sweetness. Interferes with origin character. Visible quality defect. Customer dissatisfaction. Facing Definition Burning on flat side of bean. Similar to tipping but on face. From direct contact with hot drum. Less common than tipping. Drum temperature issue. Causes Excessive drum contact heat. Drum too hot. Poor drum condition. Insufficient airflow. Static beans in drum. Prevention Proper drum temperature management. Adequate airflow (keeps beans moving). Regular drum cleaning. Appropriate rotation speed. Baking Definition Insufficient heat over extended time. Creates flat, bready, papery flavors. Beans appear even but taste underdeveloped. Lack of caramelization and Maillard development. Common beginner error. Causes Insufficient heat application. Too slow roasting. Low temperatures throughout. Attempting "gentle" roast but going too far. Lack of development time at appropriate heat. Characteristics Grainy, bready, cereal flavors. Lack of sweetness. Flat, one-dimensional. Papery, cardboard notes. Underdeveloped despite reaching color target. Prevention Adequate heat application (especially browning phase). Appropriate roast time (not too long). Proper development ratio (15-25% DTR). Trust bean development, not just time. Detection Taste reveals baking (visual may appear fine). Grainy, underdeveloped flavors. Lack of aromatics. Flatness pervasive. Cupping reveals defect clearly. Underdevelopment Definition Insufficient development time after first crack. Grassy, green, sour flavors. Roast level reached too quickly without adequate development. Color appropriate but flavor immature. Causes Dropping too soon after first crack. Development time too short (<15% DTR typically). Excessive heat through roast creating color without development. Rushing to finish. Characteristics Grassy, vegetal, hay-like. Sour, acidic (sharp not bright). Astringent, papery. Lacks sweetness. Origin characteristics not expressed. Prevention Adequate development time (minimum 15% DTR, often 18-22%). Extend time after first crack. Lower heat application allows longer development without burning. Taste evaluation essential. Over-development Definition Excessive time in development phase. Baked or roasted character dominates. Can occur at any roast level. Flat or over-roasted flavors. Time/temperature imbalance. Causes Too long at high temperature after first crack. Attempting light roast with excessive development. Temperature too low in development (drags on). Poor energy management. Impact Roasted, toasted flavors dominate. Origin character obscured. Bittersweet to bitter. Can be acceptable in dark roasts but defect in light roasts. Stalling/Crashing Definition Roast temperature plateaus or decreases instead of rising. Dramatic energy loss. Occurs when heat input insufficient for bean mass. Creates baked flavors and extended roast time. Causes Inadequate burner capacity for batch size. Too large batch. Charging beans too cold. Environmental temperature too low. Poor roaster setup. Effects Roast time extends dramatically. Baked flavors develop. Can recover but quality compromised. May never reach target temperature. Requires intervention (more heat or abort). Prevention Appropriate batch size for roaster. Preheat beans if cold storage. Adequate burner input. Environmental control. Understanding roaster capacity. Flicking/Running Away Definition Roast temperature accelerates out of control. Rate of rise increases instead of decreasing. Loss of roast control. Results in burnt or uneven development. Causes Excessive heat in browning/development. Exothermic reactions (roast produces heat) overtake control. Failure to reduce heat appropriately. Thermal momentum underestimated. Prevention Anticipate temperature momentum. Reduce heat early (before needed). Monitor rate of rise continuously. Be prepared to drop temperature or drop roast. Experience crucial. Quakers in Roast Definition Underdeveloped beans that fail to roast properly. Remain pale, tan, or light brown. Not roaster's fault (green coffee defect). Should be sorted from green or after roasting. Causes Immature beans at harvest. Underdeveloped green beans. Defective beans. Cannot be fixed by roasting. Present in green coffee. Management Sort green coffee beforehand. Visual sort of roasted coffee (hand-pick quakers). One quaker can ruin cup. Quality control essential. Charring Definition Extreme scorching creating carbonization. Blackened beans or spots. Total quality destruction. Burnt, acrid, charcoal flavors. Complete defect, no salvaging. Causes Extreme over-roasting. Equipment failure (stuck beans, flame contact). Inattention to roast. Critical error. Prevention Constant roast monitoring. Never leave roaster unattended. Proper equipment maintenance. Temperature monitoring systems. Emergency procedures known. Uneven Roasting Definition Beans in same batch at different roast levels. Color variation from light to dark in single batch. Some beans under-developed, others approaching burnt. Multiple contributing factors. Causes Mixed bean sizes in batch. Poor heat distribution in roaster. Inadequate mixing/tumbling. Varying bean densities. Green coffee inconsistency. Prevention Screen green coffee for uniform size. Proper roaster setup (airflow, drum speed). Use quality, consistent green coffee. Small batch roasting reduces risk. Insufficient Airflow Definition Inadequate air circulation through roasting beans. Creates smoke backup, uneven roasting, acrid flavors. Chaff buildup. Coffee suffocates. Heat distribution poor. Causes Chaff buildup in system. Damper closed too much. Inadequate fan/blower. System design flaws. Poor maintenance. Prevention Regular chaff cleaning. Proper damper settings. Airflow monitoring. Roaster maintenance schedule. System checks before roasting.
Related Notes: - Coffee Terminology MoC