tags: [] - coffee/roasting - coffee/education aliases: - Roasting defects module - Troubleshooting roasting module

Module 6 — Defects, Troubleshooting & Best Practices¶

Tags: #coffee/roasting #coffee/education Aliases: Roasting defects module, Troubleshooting roasting module Related: Roasting MOC | Defects & Faults | Roast Profile | Module 5 - Sensory Evaluation & Roast Quality | Coffee Chemistry Status: ✅ Complete

Overview¶

Module 6 covers roast defects — the flavour faults that arise from roasting errors or suboptimal green coffee — and the practical troubleshooting framework for identifying and correcting them. Best practices for roastery operation, equipment maintenance, and consistency are also addressed. The ability to identify roast defects and trace them to their source in the roast process is a core professional competency for roasters.

Module Content¶

6.1 — Roast Defects and Their Causes¶

Roast defects are sensory faults originating from roasting process errors — distinct from processing defects (which originate in the green coffee):

Defect	Sensory character	Roast cause
Baked	Flat; dull; stale bread; cardboard; lack of sweetness	Prolonged low-heat period; stalled RoR; insufficient energy through Maillard
Scorched / tipped	Acrid; sharp; chemical burn; harsh bitterness	Bean surface contact with drum at high temperature early in roast; too high charge temperature
Under-developed	Sour; grassy; raw; thin; bright but unpleasant	Insufficient development time; too short post-crack time
Over-developed / dark	Smoky; ashy; carbon; bitter; no origin character	Too long at high temperature; taken past second crack
Quaker (unroasted bean)	Bland; peanut; straw-like	Unripe green cherry in the lot; does not colour correctly during roasting — a green coffee issue
Uneven roast	Inconsistent cup; wide flavour variation bean-to-bean	Drum not adequately pre-heated; overloaded batch; equipment issue

6.2 — Troubleshooting Framework¶

When a defect is identified through cupping, the following systematic process isolates the cause:

Identify the defect — name the specific sensory problem using the SCA Flavour Wheel and defect vocabulary
Consult the roast log — review the profile: RoR, charge temperature, first crack time, DTR, drop temperature
Identify the likely phase — baked defects typically occur in the Maillard phase; scorched defects in the drying phase; under-development in the development phase
Adjust one variable — change only one profile variable per roast batch to isolate the effect
Re-roast and evaluate — cup the adjusted roast and compare against the original

Common diagnostic questions: - Did the RoR crash or stall? → Baked flavour risk - Was charge temperature too high? → Scorching risk - Was first crack too early (aggressive early heat)? → Under-development risk - Was development time too short (< 20% DTR)? → Under-development - Was the drop temperature too high? → Over-development / dark flavour risk

6.3 — Green Coffee Defects vs. Roast Defects¶

Not all flavour faults originate in roasting — some originate in the green coffee:

Green defect	Sensory character	Source
Ferment	Sour; vinegary; acetic; putrid	Over-fermentation during processing
Phenol / medicinal	Antiseptic; plastic	Bacterial contamination; poor processing
Musty / mould	Damp earth; mould	Improper drying; storage damage
Quaker	Peanut; straw; blank	Unripe cherry at harvest
Insect damage	Woody; phenolic	Coffee Berry Borer (Hypothenemus hampei)

Green coffee defects cannot be fixed by roast adjustment — they must be addressed at source (better green selection, processing improvement, defect sorting).

See Defects & Faults for the complete green coffee defect reference.

6.4 — Roastery Best Practices¶

Consistency: - Maintain identical batch weight within ±5% of rated capacity - Pre-heat drum to the same charge temperature for every batch - Allow consistent rest time between roast batches - Log every roast; compare against reference profiles

Equipment maintenance: - Clean chaff collector after every session — chaff accumulation is a fire risk - Descale drum and roast chamber regularly - Calibrate temperature probes periodically; probe drift causes profile inaccuracy - Inspect cooling tray bearings and agitator regularly

Cooling: - Coffee must reach ambient temperature rapidly — slow cooling extends the effective roast and increases development; rapid cooling with forced air is standard - Target: below 40°C within 5 minutes of drop

Safety: - Chaff is highly combustible; the chaff collector must be kept clean - Maintain a fire suppression system rated for electrical and chaff fires - Never leave a drum roaster unattended during a roast cycle

Key Facts¶

Baked roast (flat, dull, cardboard) is caused by stalled RoR — insufficient energy through the Maillard phase
Scorched / tipped roast is caused by excessive drum surface contact at high temperature early in the roast
Under-development (sour, grassy, thin) results from insufficient development time post-first-crack
Green coffee defects (ferment, phenol, quaker) cannot be corrected through roast adjustment — they must be addressed in green selection
Chaff accumulation is the primary fire risk in roastery operations; regular cleaning is safety-critical

References¶

Changelog¶

Date	Change
2026-04-29	Note created

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