Home Roasting Troubleshooting Guide- by Raihaan Esat

Creating Comprehensive Troubleshooting Guides for Common Coffee Roasting Defects

 

Common Roasting Defects Overview

When developing these troubleshooting guides, I first wanted to establish a foundational understanding of coffee roasting defects. Based on my knowledge of the coffee industry and the specific needs of ICT's client base (which ranges from home roasters to small businesses handling 60-80kg/week to large roasters processing 1-2 tonnes), I've identified the most common issues that occur during the roasting process.

Coffee roasting defects generally fall into three categories:

1. Flavor-related defects (taste issues)
2. Physical defects (appearance issues)
3. Equipment-related problems

These guides are designed to help My clients identify and resolve issues quickly, which aligns with ICT's positioning as a knowledge leader in the industry. ICT "acts as a buyers agent for coffee roasters" and provides "resources, training, and business support" - these guides are a distillation of knowledge from working and consulting with coffee roasters globally.

Flavor-Related Defects Guide

Underdeveloped Roast (Grassy/Sour)

Problem: Coffee tastes grassy, hay-like, or excessively sour/acidic Possible Causes:

• Insufficient development time
• Too low charge temperature
• Too quick drying phase
• Low finish temperature
• 3 phases out of alignment (green to yellow, yellow to FC, Fc to end)

Solutions:

1. Extend development time after first crack (aim for 18-25% of total roast time)for espresso
2. reduce charge temperature by 5-10°C
3. Slow down initial drying phase by reducing charge temperature or apply less heat initially.
4. Monitor rate of rise (RoR) and aim for a gentle declining curve (Scott Rao technique)

 

Overdeveloped Roast (Bitter/Flat)

Problem: Coffee tastes bitter, ashy, or lacks clarity

Possible Causes:

• Extended development time
• Too high finishing temperature
• Increased velocity during development phase

Solutions:

1. Shorten development time after first crack
2. Lower end temperature by 3-5°C
3. Maintain momentum through development phase with appropriate heat application
4. Consider lighter roast profiles for certain origin characteristics

 

Baked Flavor (Flat/Cardboard-like)

Problem: Coffee tastes flat, papery, or like cardboard Possible Causes:

• Stalling  of the roast curve post  FC
• Inconsistent heat application through the middle of the roast
• Extended middle phase (between drying and first crack)

Solutions:

1. Maintain a consistent declining rate of rise throughout the roast
2. Avoid dramatic heat adjustments mid-roast
3. Shorten the middle phase of the roast
4. Apply heat more aggressively early in the roast, then taper down progressively without stalling.

 

Physical Defects Guide

Tipping

Problem: Small dark/black spots on bean tips Possible Causes:

• Too high charge temperature
• Too rapid heat application early in roast
• Too much heat during FC
• Beans with high moisture content

Solutions:

1. Reduce charge temperature by 5-10°C
2. Apply heat more gradually during the drying phase
3. Adjust airflow to better control moisture evacuation
4. Consider longer drying phases for high-moisture beans

Scorching

Problem: Dark spots or patches on bean surfaces Possible Causes:

• Uneven heat distribution in drum
• Insufficient drum rotation speed
• Poor airflow
• Over loaded drum

Solutions:

1. Check and clean heating elements for even distribution
2. Increase drum rotation speed if possible
3. Improve airflow to prevent hot spots
4. Reduce batch size to ensure proper bean movement

Uneven Roast Development

Problem: Inconsistent color across bean batch Possible Causes:

• Inconsistent green bean size
• Poor air circulation
• Improper bean density sorting

Solutions:

1. Screen beans for more consistent size before roasting
2. Adjust airflow to improve circulation
3. Sort beans by density when possible
4. Consider longer development times for more even results
5. Ensure proper maintenance of roasting equipment

Equipment-Related Issues

Temperature Probe Issues

Problem: Inconsistent or inaccurate temperature readings Possible Causes:

• Probe placement issues
• Probe calibration drift
• Carbon buildup on probes

Solutions:

1. Verify and adjust probe placement for accurate readings
2. Recalibrate temperature probes regularly
3. Clean probes after every 8-10 weeks
4. Consider adding secondary probes for verification

 

 

 

 

Airflow Problems

Problem: Difficulty controlling roast development or smoke Possible Causes:

• Clogged exhaust systems
• Worn/damaged fan fins
• Improper damper settings

Solutions:

1. Establish regular cleaning schedule for exhaust systems
2. Check and maintain fan motors quarterly
3. Document optimal damper settings for different bean types
4. Consider upgrading airflow control systems for more precision

Drum Speed Inconsistencies

Problem: Uneven bean movement or development Possible Causes:

• Worn drive belts
• Motor issues
• Overloaded drum
• Warped drum

Solutions:

1. Inspect and replace drive belts as needed
2. Schedule regular motor maintenance
3. Adhere to manufacturer's recommended batch sizes
4. Clean drum surfaces to prevent bean drag