Changes in coffee roasting: what are the chemical changes in the roasting process of coffee beans

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Do you know what happens when roasting coffee beans? What are the chemical changes that transform raw coffee beans into coffee ripe beans with charming flavor and rich aroma?

Major chemical reactions

Heating coffee beans triggers hundreds of different chemical reactions. Baking degrades some compounds, changes others, and produces new ones.

You may have heard someone say that when an organic substance is heated above its decomposition temperature, it produces volatile compounds and leaves solid residues containing large amounts of carbonization or coke. During coffee roasting, we avoid overheating coffee beans to cause carbonization, but they do undergo chemical changes associated with pyrolysis, including caramelization and the production of volatile compounds.

Here are the main chemical changes that come with baking:

Maynard reaction

This reaction occurs at about 150 ℃, when the coffee beans are still absorbing heat and continue to release heat during the baking process. Calories lead to reactions between carbohydrates and amino acids in beans, leading to changes in color, taste and nutrients.

The color change is mainly due to the production of melanin, which not only turns the coffee beans brown, but also affects the taste and mellow thickness of the coffee.

Any small change in the temperature and time of Maynard's reaction at this stage may have a great impact on the final flavor.

Coffee that takes a longer time in the Maynard reaction increases its viscosity, while a shorter Maynard reaction produces more sweetness and acidity, because if Maynard takes too long, the acid and the acid that converts to sweetness will be destroyed.

When the bean baker experimented with baking techniques, it also included changing the length and intensity of Maynard's reaction and recording how these changes would affect the final flavor.

Degradation reaction

This procedure depends on the Mena reaction, in which amino acids react with carbonyl groups to produce compounds such as aldehydes and ketones. The baker does not need to know exactly what these compounds are. it is important to recognize that this reaction is indispensable for compounds that produce aromas and flavors.

Caramelization of carbohydrates

When heated to about 170 ℃, the heat breaks down large amounts of complex carbohydrates into smaller sugar molecules that can be dissolved in water, indicating an increase in the sweetness of the final coffee. This reaction continues until the end of the baking process, and it also contributes to the sweet aromas of coffee, such as caramel and almonds.