Coffee roasting is the process of heating green coffee beans

to transform them into aromatic, flavorful roasted beans for brewing

Roasting develops the bean’s color, aroma, acidity, sweetness, and body.

The Roasting process

1. Green Coffee Beans

  • State: Raw, unroasted beans; green to bluish-green, dense, with ~10–12% moisture.

  • Goal: Transform into aromatic, flavorful roasted coffee.

2. Preheating & Loading

  • Process: The roaster is preheated to the target starting temperature, and beans are loaded.

  • Purpose: Ensures even heat distribution for consistent roasting.

3. Drying Stage (100–160°C / 212–320°F)

  • Duration: ~4–8 minutes.

  • Changes:

    • Beans lose moisture (weight loss of ~2–5%).

    • Color changes from green → yellow.

    • Aroma: grassy or hay-like.

  • Purpose: Prepares beans for browning without scorching.

4. Browning Stage / Maillard Reaction (160–196°C / 320–385°F)

  • Chemical Changes:

    • Amino acids react with sugars → melanoidins → brown color and complex flavors.

    • Caramelization of sugars begins.

  • Physical Changes: Beans expand slightly; color shifts from yellow → light brown.

  • Aroma: Nutty, sweet, toasted.

  • Purpose: Develops most of the coffee’s flavor and aroma.

5. First Crack (~196°C / 385°F)

  • Physical Event: Beans crack audibly due to internal pressure from expanding water vapor and CO₂.

  • Roast Level: Light to medium roasts often stop here.

  • Characteristics:

    • Sweetness and acidity are prominent.

    • Surface remains dry; oils not yet visible.

  • Purpose: Marks a major milestone in flavor development.

6. Development / Roast Control (196–224°C / 385–435°F)

  • Process: Roaster adjusts time and temperature after first crack to fine-tune flavor.

  • Flavor: Balances acidity, sweetness, and body; preserves origin character.

  • Purpose: Ensures beans reach the target roast profile without overcooking.

7. Second Crack (~224–230°C / 435–446°F)

  • Physical Event: Another audible crack; oils appear on the surface.

  • Roast Level: Medium-dark to dark roasts.

  • Flavor Changes:

    • Bitterness increases; acidity decreases.

    • Smoky, chocolatey, or caramelized notes dominate.

8. Cooling

  • Process: Rapid cooling via air or water mist stops roasting immediately.

  • Purpose: Prevents over-roasting, preserves flavor, and stabilizes beans for storage.

9. Post-Roast Handling

  • Degassing: Beans release CO₂ for hours to days, affecting flavor extraction.

  • Packaging: Airtight storage (often with one-way valves) maintains freshness.

Key Variables in Roasting

  • Bean origin & density: Denser beans roast slower; lighter beans faster.

  • Roast profile: Time-temperature curve dictates flavor balance.

  • Roaster type: Drum, air, or fluid-bed roasters affect heat transfer and roast uniformity.

  • Batch size: Larger batches require longer roasting for even heat penetration.