Coffee roasting is both an art and a science, requiring precision, experience, and a deep understanding of how heat transforms green coffee beans into aromatic, flavorful gems. In recent discussions among coffee enthusiasts, several key roasting concepts have emerged as critical to achieving the perfect roast: dehydration, temperature climb, smoke exhaust control, and sliding. This article explores these techniques in depth, offering practical insights for both beginners and experienced roasters.

Understanding Dehydration in Coffee Roasting

What is Dehydration?

Dehydration refers to the initial phase of roasting, typically below 170°C (338°F), where moisture inside the beans evaporates. This stage is crucial because improper dehydration can lead to uneven roasting or baked flavors.

Optimal Dehydration Time

Ideal Duration: 5–8 minutes (varies by machine and bean moisture). 

New vs. Old Beans:

New crop beans (higher moisture, 12–14%) require longer dehydration (7–8 min). 

Older beans (lower moisture, ~10–12%) need shorter dehydration (5–6 min). 

Why It Matters

Ensures even heat penetration. 

Prevents scorching or underdeveloped flavors. 

Sets the foundation for Maillard reactions and caramelization. 

Mastering Temperature Climb (Rate of Rise)

What is Temperature Climb?

This refers to the rate at which bean temperature increases during roasting, usually measured in °C per minute. 

Ideal Temperature Climb Rates

General Range: 7–14°C/min (best around 10°C/min for balance). 

Adjusting for Bean Type:

Hard beans / high-moisture beans (e.g., new crop): Slower climb (~7–9°C/min). 

Soft / low-moisture beans: Faster climb (~11–14°C/min). 

Key Considerations

– Too fast → Underdeveloped, grassy flavors. 

– Too slow → Baked, dull taste. 

Firepower control  is critical—gradual adjustments prevent drastic swings. 

Managing Smoke Exhaust for Cleaner Roasts

When Does Smoke Appear?

– 180°C (356°F): Smoke becomes noticeable. 

– First Crack (195–205°C / 383–401°F): Smoke increases significantly. 

– Second Crack (225–230°C / 437–446°F): Peak smoke production (especially in dark roasts). 

How to Avoid Smoky Off-Flavors

– Fully open exhaust vents after first crack to prevent smoke buildup. 

– Darker roasts need more airflow—linger too long, and smoky flavors dominate. 

– Proper ventilation is essential for consistency. 

The Technique of Sliding (Residual Heat Roasting)

What is Sliding?

Sliding involves reducing or cutting heat and letting beans roast via residual boiler heat and exothermic bean reactions (especially during cracks). 

When to Use Sliding

– Best for medium-dark roasts (post-first crack, pre-second crack). 

– Avoid for light roasts—can lead to underdevelopment. 

Benefits of Sliding

– Smoother, more balanced flavor (avoids harsh, burnt notes). 

– Mimics “simmering” for even heat distribution. 

– Reduces risk of tipping or scorching. 

Key Precautions

– Do not slide too long—can flatten acidity and mute origin character. 

– Cool beans rapidly post-slide (fast airflow locks in flavors). 

Additional Roasting Best Practices

1. Rapid Cooling is Essential

The faster beans cool, the better flavor retention. Use strong airflow for best results. 

2. Optimal Roast Time

12–15 minutes (for 250g / half-pound batches) is ideal for balanced development. 

Espresso roasts may need longer (15–18 min) for deeper body. 

3. Oil Development & Freshness

Oily beans = richer flavor but oxidize faster. 

Over-roasting creates excessive oil—consume within days to avoid staleness. 

Conclusion: Crafting the Perfect Roast

Mastering dehydration, temperature control, smoke management, and sliding separates good roasts from exceptional ones. Each variable interacts with bean moisture, density, and roast level, requiring adjustments based on: 

Bean type (hard vs. soft, new vs. old). 

Roast degree (light, medium, dark). 

Machine dynamics (drum vs. air roaster). 

By fine-tuning these elements, roasters can highlight a coffee’s natural sweetness, acidity, and body—whether aiming for a bright, floral Gesha or a chocolatey Blue Mountain profile. 

Want to experiment? Try adjusting one variable at a time and cupping the differences. Happy roasting! 

Have questions or personal roasting tips? Share them in the comments!