1. Maillard Reaction
The Maillard reaction is one of the most important chemical reactions in the coffee roasting process. This reaction occurs between amino acids and reducing sugars in the coffee beans, producing a variety of new compounds with characteristic flavors and colors:
- Process: Starts at approximately 150°C and intensifies as the temperature increases.
- Products: Produces melanoidin compounds with a brown color, contributing to bittersweet flavors and distinctive aromas such as toasted bread, caramel, and other roasted flavors.
- Role: The Maillard reaction is the primary cause of the brown color and many of the complex flavors in roasted coffee.
Indeed, the Maillard reaction and other thermal processes involved in coffee roasting lead to the formation of various important classes of flavor compounds, including:
• Furans: Contribute to sweet, caramel-like, and roasted flavors.
• Pyrazines: Impart nutty, earthy, and roasted characteristics.
• Pyrroles: Add to the overall roasted and baked aromas.
• Oxazoles: Provide spicy and sweet notes.
• Thiophenes: Contribute to meaty, savory, and roasted flavors.
• Thiazoles: Impart meaty, roasted, and slightly sulfurous flavors.
• Other heterocyclic compounds: These include a wide range of complex molecules that contribute to the intricate and rich flavor profile of roasted coffee.
These compounds play a crucial role in defining the unique and desirable sensory attributes of coffee, making the roasting process essential for developing the final flavor profile of the beans.
2. Caramelization
Caramelization is the thermal decomposition of sugars in the coffee beans, creating compounds with sweet and bitter flavors:
- Process: Begins at approximately 170°C.
- Products: Produces compounds like furan, maltol, and ethyl maltol, which impart caramel, fruity, and nutty flavors.
- Role: Caramelization initially increases sweetness by creating characteristic caramel flavors. As the process continues, it can also lead to increased bitterness.
Caramelization Process in Coffee Roasting:
• Initial Stages: During the initial stages of caramelization, sugars break down and form various compounds that impart sweet, caramel-like flavors to the coffee.
• Later Stages: As caramelization progresses and temperatures increase, these sugars continue to break down, leading to the formation of more complex compounds that can introduce bitter flavors.
3. Decomposition of Chlorogenic Acids (CGA)
Chlorogenic acids are one of the most important organic acids in green coffee beans, accounting for about 7-10% of the dry weight:
- Process: CGA is decomposed into quinic acid and caffeic acid during roasting.
- Products: Quinic acid and caffeic acid contribute to the acidity and body of the coffee.
- Role: The decomposition of CGA affects the acidity and tanginess of the coffee. Arabica coffee typically has less CGA than Robusta, resulting in a milder acidity.
4. Decomposition of Trigonelline
Trigonelline is an important alkaloid in green coffee beans, accounting for about 1% of the dry weight:
- Process: During roasting, trigonelline is decomposed into niacin (vitamin B3) and pyridine compounds.
- Products: Niacin and pyridine create many bitter flavors and characteristic aromas.
- Role: The decomposition of trigonelline contributes to the flavor and aroma of the coffee while providing niacin (vitamin B3) beneficial to health.
5. Degassing and Oil Formation
During roasting, coffee beans release gases such as CO2 and water vapor, and oil compounds within the beans begin to migrate to the surface:
- Degassing: The degassing process is vigorous during the first crack and continues to the second crack. This is when CO2 and water vapor accumulated inside the beans are released.
- Oil Formation: As the beans reach high temperatures in the final stages of roasting, oils begin to appear on the surface, especially evident in dark roasts.
[ Questions for Chemical Reactions in the Roasting Process ]
1. At what temperature does the Maillard reaction start?
- A. 140°C
- B. 120°C
- C. 100°C
- D. 160°C
2. At what temperature does caramelization start?
- A. 160°C
- B. 140°C
- C. 180°C
- D. 200°C
3. What are the products of chlorogenic acids (CGA) decomposition during roasting?
- A. Quinic acid and caffeic acid
- B. Melanoidin
- C. Furan and Maltol
- D. Niacin and pyridine
4. What does trigonelline decompose into during roasting?
- A. Niacin and pyridine
- B. Furan and maltol
- C. Quinic acid and caffeic acid
- D. Melanoidin
5. What gases do coffee beans release during roasting?
- A. Water vapor and CO2
- B. O2 and CO2
- C. H2 and O2
- D. N2 and CO2
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