Why do coffee beans turn brown after roasting? Why is there an aroma?

Coffee beans are light green and turn brown when roasted. This baking characteristic brown mainly comes from the brown pigment produced by oligosaccharins, amino acids and chlorogenic acids. The so-called brown pigment does not refer to a color or ingredient, but a general term for the many ingredients that make coffee different colors.

The color of raw beans changes gradually during baking because of the change in the total amount of brown pigment and the proportion of its molecular size. Brown pigments can be classified according to molecular size. Shallow baking will mostly produce small molecular pigments. With the deeper the baking degree, the total amount of pigments will gradually increase, and the proportion of macromolecular pigments will also increase.

Light baked beans mostly contain small yellowish pigments, which are chemical reaction products in the early stage of baking and substances produced by the reaction between oligosaccharides and chlorogenic acids.

If you continue baking, the oligosaccharides will be caramelized to produce caramel pigments. Coupled with the molasses pigment (Melanoidin) produced by the reaction of oligosaccharides with amino acids, a slightly larger reddish brown pigment occurs. The reaction produced by molasses pigment is called Mena browning reaction (Maillard reactions), which is a very important kind of food chemical reaction. The color and flavor of toast and the color of soy sauce are all the result of Mena's browning reaction.

If you continue to bake, proteins and polysaccharides are also added to turn into a black-brown pigment with more than a hundred times the size of the molecule.

This pigment is actually one of the elements that make up the bitterness of coffee. It is generally believed that the larger the molecule of the pigment, the stronger the bitterness of the coffee and the heavier the taste. Therefore, the intensity and taste of bitterness will change with the degree of roasting of coffee, which is affected by these pigment changes.

The reason for the aroma of coffee:

Coffee raw bean moon has two hundred aroma components, but those aromas are not comfortable for us. What makes the aroma of coffee attractive is the baptism of roasting and the many aroma components produced by roasting (there are 700 known ingredients alone). Compared with the ingredients that make up the taste of coffee, although the components of each aroma are small, they have a great impact, and they can even be said to be the main ingredients of coffee.

The last part mentioned that coffee roasting produces Mena browning reaction, which also plays an important role in the formation of coffee aroma. Flavor increase, soy sauce, or barbecue, bread have a unique aroma, these are the secondary results of Mena browning reaction. So is the aroma of coffee. What kind of aroma can be played to what extent depends on the arrangement and combination of amino acids and heating conditions. Coffee contains a variety of amino acids, but the arrangement and combination of amino acids is affected by varieties, planting conditions, delicate methods and so on, so different raw beans have different aroma. In addition, even if the same raw beans are used, the increase in temperature and roasting degree of roasted coffee beans will also change the aroma.

The caramelization mentioned in the previous section is also one of the chemical reactions that create the aroma of coffee. When caramel is produced, it will emit volatile acid, and its aroma and sweet aroma are important elements of coffee aroma. Other substances such as chlorogenic acid will also produce aroma when heated.

Baking produces many aroma components that vary depending on the degree of baking. The changed patterns can be roughly divided into three categories: 1. A substance with less change; 2. A substance that begins to decrease after increasing to a certain extent; 3. A substance that increases gradually during baking. 1. It is mostly regarded as the ingredient in raw beans; 3. It is usually considered to be a smoky or pungent ingredient; 2. For us, it is an ingredient that brings comfortable sweet and sour aromas or baked sweet aromas. The reason why the different baking degree can change the texture and intensity of the aroma is due to the change of the total amount and balance of the above three aroma components.