Caramelization in Coffee Roasting: Understanding Sugar Oxidation and Browning

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FrontStreet Coffee shares insights about caramelization (the oxidation and browning of sugars) and the Maillard reaction during coffee roasting.

The Source of Coffee Aroma

We often say that coffee is aromatic, but where does this fragrance come from? Coffee beans themselves store abundant raw materials such as carbohydrates, proteins, lipids, organic acids, and more. When heated during roasting, these initiate a series of complex reactions that create enticing aromas. There are two reactions in the roasting process that must be mentioned.

Key Reactions in Coffee Roasting

Caramelization (the oxidation and browning of sugars) and the Maillard reaction (the reaction between amino acids and sugars).

Both reactions require the participation of sugars, and the sucrose content rich in green beans provides exactly the materials needed for these two reactions. Previous studies have also found a positive correlation between sucrose content and coffee bean flavor.

The Maillard Reaction

Subtle changes in temperature and duration during the Maillard reaction can greatly affect the final flavor of coffee.

A longer Maillard reaction will increase the viscosity of coffee, while a relatively shorter Maillard reaction will bring more sweetness and acidity to the coffee beans. This is because the fruity notes and sweetness contributed by acidity in coffee will be destroyed by an overly prolonged Maillard reaction.

Caramelization

The sugars in coffee beans undergo caramelization at approximately 170-200°C, which coincides with the melting point of sucrose (185°C) and the temperature during the first crack stage of coffee bean roasting. The products of caramelization are divided into two parts:

The dehydration products of sugars, which are caramel or sauce-colored decomposition products, mainly some volatile aldehydes and ketones.

In general, caramelization produces roasted aromas, caramel, and color, as well as other aromatic substances such as maltol, cyclotene, furan compounds, etc. These compounds can also be found in foods like red wine, fruit juice, and cream.

However, if caramelization goes too far during the roasting process, it will cause carbonization, making the coffee dry, bitter, and harsh on the throat. Insufficient caramelization will result in monotonous, dull aromas lacking complexity.

Conclusion

However, if the Maillard reaction and caramelization in coffee are恰到好处 (just right), preserving the high-quality acidity in coffee, it best represents the inherent flavor of the coffee beans.

Important Notice :

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