Analysis on the color change of raw coffee beans during roasting one of the reasons for the formation of coffee bitterness

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Everyone knows that the color of raw coffee beans is light green, dark green, dark green and yellowing on the surface. The color of raw coffee beans obtained by different processing methods is also different, but the color after baking is all brown. Why? This is a brown pigment made from oligosaccharides, amino acids, chlorogenic acid and other substances. Brown pigment does not refer to a simple color or substance, it is a general term for the various ingredients that make coffee beans different colors.

Raw beans constantly change color during baking, depending on the number of brown pigments and the size of molecules. Brown pigments can be classified according to the size of molecules, shallow baking will mostly produce small molecular pigments, with the deepening of baking, the total amount of pigments will increase, and the proportion of macromolecular pigments will also increase.

Most of the lightly roasted coffee beans contain small yellow pigments, which are produced by the reaction of oligosaccharide thermal decomposition with chlorogenic acid. Continue baking, oligosaccharides will be caramelized to produce caramel pigment, oligosaccharides react with amino acids to produce molasses pigment, which will produce a slightly larger reddish-brown pigment. The reaction produced by molasses pigment is called Mena reaction, which is a very important kind of food chemical reaction. The color of toast, miso and soy sauce are all the result of Mena's reaction.

If the baking continues, proteins and polysaccharides are also added to the reaction, turning into a huge dark brown pigment. This pigment is one of the elements that make up the bitterness of coffee.