Roasting & Roast Levels
Roasting and Roast Levels
#coffee/roasting #coffee/theory #note
The roasting process transforms green coffee beans into soluble, aromatic beans. Roasting determines the balance between the origin characteristics of the bean and the flavours introduced by the roast itself.
1. Differences Between Roast Levels
Roast level affects density, solubility, acidity, and flavour profile:
| Feature | Light Roast | Medium Roast | Dark Roast |
|---|---|---|---|
| Color | Light brown, matte surface. | Medium brown, dry surface. | Dark brown, oily surface. |
| Acidity | High, bright, fruit-forward. | Balanced, sweet, malic/citric. | Low, muted, carbonic. |
| Body | Light, tea-like or juicy. | Medium, silky or smooth. | Heavy, thick, coating. |
| Flavours | Origin characteristics, floral, citrus. | Caramel, milk chocolate, stone fruit. | Dark chocolate, nuts, smoke, ash. |
| Solubility | Low. Requires hotter water (93-96°C). | Moderate. Water temp around 90-93°C. | High. Easy to extract (85-90°C). |
| Bean Density | High (harder to grind). | Moderate. | Low (brittle, easy to grind). |
2. Roasting Physics and Techniques
During a roast, heat is transferred to the coffee beans via conduction, convection, and radiation:
Heat Transfer Methods
- Convection (Air Roasting): Heat transfer via hot air flowing through the bean bed. It produces a very even, clean roast with less risk of scorching.
- Conduction (Drum Roasting): Heat transfer via direct contact with the hot metal walls of the roasting drum. This can enhance body and sweetness but requires careful drum temperature management.
Roasting Milestones
- Drying Phase: The green beans lose moisture. They turn yellow and begin to smell like bread or hay.
- Maillard Reaction: Amino acids and reducing sugars react, creating complex aroma compounds and browning the beans.
- First Crack (around 196°C): Moisture inside the bean vaporizes, causing the bean to expand and crack open with a popping sound.
- Light roasts are dropped shortly after the first crack finishes.
- Medium roasts are developed slightly longer during the development phase.
- Dark roasts are roasted until the second crack (oil migrates to the surface, cell structure breaks down).
Rate of Rise (RoR)
RoR is the speed at which the bean temperature increases during the roast (measured in degrees per minute). A declining RoR is generally preferred to avoid baked flavours (stagnant RoR) or scorched/underdeveloped cores (surging RoR).
3. References & Further Reading
- Scott Rao Resources:
- Coffee Roasting: Best Practices (Book) — Advanced study on Rate of Rise curves and development time ratios.
- Scott Rao's Official Blog — Professional articles and roasting guides.
- James Hoffmann Resources:
- Coffee Roasting Explained (YouTube) — An introductory video explaining the physical and chemical phases of roasting.
See Also
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