Airflow Control for Convection Coffee Roasting

Mastering airflow control is crucial for perfect coffee roasts. Here’s what you need to know:

Convection roasting uses hot air to cook beans evenly from inside out. Proper airflow affects heat transfer, roast consistency, and flavor development. Adjust airflow throughout the roast:

• Start: Low (10-50%) for gentle drying
• Middle: Medium (50-75%) for balanced development
• End: High (50-100%) to remove smoke and lock in flavor

Key airflow control methods:

• Damper systems: Simple, cost-effective, less precise
• Variable Speed Drive (VSD) systems: Highly accurate, automatable, more expensive

Tips:

• Clean your roaster regularly
• Adjust settings based on coffee type and desired flavor profile
• Keep detailed notes on settings and outcomes

There’s no one-size-fits-all approach. Experiment to find what works best for your beans and roaster.

Feature	Damper Systems	VSD Systems
Control Method	Adjustable plates	Fan speed adjustment
Precision	Moderate	High
Cost	Lower	Higher
Ease of Use	Simple	More complex
Automation	Limited	Fully automatable

Related video from YouTube

How Airflow Works in Coffee Roasting

Coffee roasting relies on careful control of heat and air. Let’s break down how airflow impacts the process and final flavor.

Heat Transfer and Airflow

Heat transfer happens in two main ways:

1. Conduction: Heat moves directly from hot drum to coffee beans.

2. Convection: Hot air moves around beans, cooking them from inside out.

Heat Transfer Method	How It Works	Impact on Roasting
Conduction	Direct contact between beans and hot drum	Cooks beans from outside in
Convection	Hot air passes over beans	Cooks beans from inside out

In a typical drum roaster, about 70% is convection, 30% conduction. This mix allows for balanced roast development.

"In the most general sense, conductive heat transfer is where you are going to lock in flavors and sweetness… convective heat transfer will help to find and give you greater clarity with those flavors." – Bill Kennedy, The San Franciscan Roaster Co.

How Airflow Changes Flavor

Airflow directly impacts coffee taste:

• Low airflow: Can lead to "baked" taste
• High airflow: Might cause tipping and sourness

Many roasters adjust airflow throughout the roast:

1. Start: Less airflow to let heat into bean
2. Middle: Increase as beans dry out
3. End: Highest to control final flavor development

One roaster’s successful settings on a North TJ-067:

• 0-90 seconds: 18% (minimum air)
• 90 seconds to first crack: 45%
• First crack to end: 60%

Remember, these aren’t universal. Experiment to find what works for you.

"Airflow is one of the key mechanisms by which taste, aroma, and color are developed by air through the roast… Air is critical for heat transfer, for the combustion of gas, and it is critical for the development of the coffee." – Don Cox, Bald Guy Brew

Types of Airflow Control Systems

Damper Systems

Use adjustable plates to regulate airflow.

Pros:

• Simple to use
• Cost-effective
• Quick adjustments

Cons:

• May require manual adjustments
• Less precise control

Variable Speed Drive (VSD) Systems

Control fan motor speed to adjust airflow.

Pros:

• Highly accurate control
• Can be automated
• Smooth adjustments

Cons:

• Higher initial cost
• May require more maintenance

Feature	Damper Systems	VSD Systems
Control Method	Adjustable plates	Fan speed adjustment
Precision	Moderate	High
Cost	Lower	Higher
Ease of Use	Simple	More complex
Automation	Limited	Fully automatable

Consider your roasting needs and budget when choosing. Many roasters have built-in controls adjustable manually.

Setting Up Your Roaster’s Airflow

1. Calibrate your damper
2. Use the control panel (usually 0-100 dial)
3. Set three basic levels: Low, Medium, High

Use a lighter at trier port to check airflow:

Airflow Level	Flame Behavior
Low	Bends into chute at 45° angle
Medium	Bends heavily into chute
High	Lights but extinguishes quickly

Many roasters have digital drum pressure gauges. Higher readings mean more airflow. Monitor changes and keep a log.

"It’s your roaster and your coffee. You can do things anyway you want, but getting airflow dialed in is a very good place to start." – Mill City Roasters

Pro tip: Consider a Dwyer Magnehelic gauge for more precise measurements.

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Changing Airflow During Roasting

Adjust airflow throughout for best flavor:

Low Airflow: Start to Drying End

• Set to lowest setting
• Keep until beans stop looking wet and shiny

"If you have too much convective heat [airflow] at the beginning of the roast, you are removing moisture too quickly… We want the drying to happen but we don’t want the beans to become so dry that we lose flavor notes." – Don Cox, Bald Guy Brew

Medium Airflow: Drying End to Pre-First Crack

• Gradually increase to about 50-60% of max
• Watch for color changes
• Listen for first crack approaching

High Airflow: First Crack to Finish

• Crank up airflow
• Removes smoke that can make coffee bitter
• Helps control temperature

Roast Stage	Airflow Level	Why It Matters
Start to Drying End	Low	Allows proper drying without scorching
Drying End to Pre-First Crack	Medium	Enhances flavor development
First Crack to Finish	High	Removes smoke, controls temperature

These are guidelines. Different coffees might need tweaks. Keep notes on what works best for each bean type.

Fixing Common Airflow Problems

Not Enough Airflow

Signs:

• Uneven roasting
• Longer roasting times
• Grassy and grainy flavors

Fix:

1. Increase fan speed
2. Adjust damper settings
3. Clean exhaust system

"Airflow is a great first thing to check." – Arno Holschuh, Coffee Technicians Guild

Too Much Airflow

Can cause fast roasts and uneven flavor.

Fix:

1. Reduce fan speed
2. Adjust damper to decrease airflow
3. Check manufacturer settings

Adjusting for Different Coffees

Coffee Type	Airflow Adjustment
Natural Process	Less airflow during drying
Washed Coffee	Standard airflow profile
Dense Beans	May need higher airflow
Light Roasts	Higher airflow near end
Dark Roasts	Lower airflow near end

To fine-tune:

1. Change one variable at a time
2. Use a lighter to check airflow levels
3. Monitor drum pressure for changes

Advanced Airflow Methods

Airflow Profiles for Flavor

• Start low, finish high for sweetness and clarity
• Natural coffees: Less airflow during drying, then increase

"For natural processed coffees, I prefer less airflow during the drying phase, gradually increasing it post-first-crack to enhance sweetness and fruitiness." – Michael McIntyre, Catalyst Coffee Consulting

Airflow for Different Batch Sizes

Batch Size	Airflow Adjustment
Smaller	Decrease airflow
Larger	Increase airflow

Balancing Airflow with Other Factors

1. Temperature: Higher temps need more airflow
2. Drum speed: Faster speeds often require more airflow
3. Bean density: Dense beans might need higher airflow

"Changing those ratios between conductive and convective [heat transfer], that is where the craft roaster changes the outcome." – Bill Kennedy, The San Franciscan Roaster Co.

Keeping Airflow Steady

Regular Cleaning

Daily:

• Empty chaff collector
• Vacuum loose chaff and debris
• Wipe down cooling tray

Weekly:

• Use 5:1 water to Simple Green solution
• Soak impeller fan and chaff filter basket
• Wipe off coffee oils

Checking for Blockages

Area	Frequency	Action
Chaff collector	Every 3-5 roasts	Clean thoroughly
Cooling tray	Daily	Remove debris
Ventilation	Weekly	Check for obstructions
Fan compartment	Monthly	Remove and clean

Long-term Maintenance Plan

• Daily: Basic cleaning
• Weekly: Deep clean chaff collector and cooling tray
• Monthly: Clean hard-to-reach areas
• Every 2,000 hours: Replace bearings
• Yearly: Tune roaster ignition

"The biggest issue we see, when a roaster ignores something that feels off, would be damage to the drum or the drum actually seizing." – Nicholas Flatoff, Usonian Systems

Conclusion

Mastering airflow control is key to great coffee roasts. It impacts heat transfer, flavor development, and chaff/smoke removal.

Quick recap:

Stage	Airflow	Purpose
Start to Drying End	10-50%	Gentle heat application
Drying End to Pre-First Crack	50-75%	Balanced development
First Crack to Finish	50-100%	Smoke removal, flavor lock-in

"Proper airflow through your roasting system is of the utmost importance for the accomplishment of roasting profiles." – Willem Boot

To improve:

1. Keep detailed notes
2. Clean your roaster regularly
3. Adjust based on coffee type and desired flavor

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