Analysis of the aroma of coffee from a chemical point of view

Whether you are a coffee expert or a coffee lover, you will be attracted by the alluring aroma of that cup of freshly ground coffee every morning. What you don't know is that this aroma actually contains thousands of chemicals. To give you a better understanding of the chemical components of coffee aroma, we have drawn the following chart:

With so many complex chemical symbols, you may be looking for what makes coffee bitter and what makes coffee refreshing. Unfortunately, the chemicals that make coffee refreshing are not among them. The caffeine you need every day is odorless and tasteless. In addition, the chemical elements that we thought were the most representative of coffee are not shown in the above chart. At this point, you may suddenly realize that most of the chemicals that make up coffee aroma are unknown.

Since we are talking about coffee aroma today, we have to mention volatile compounds, that is, chemical components that are highly volatile at room temperature and atmospheric pressure. Only those chemicals that evaporate into the air can be detected by our olfactory organs. Larger chemical molecules, such as melanin, which gives coffee its black appearance, are inherently less volatile and therefore do not count as coffee aroma. Where do these volatile compounds come from?

There are many reasons for the chemical components in coffee aroma, but overall, roasting is the most important factor affecting coffee aroma. Among them, Maillard reaction, that is, the interaction between protein and sugar in coffee, is the most obvious. In addition, the decay and decomposition of other substances will also produce a large number of aromatic elements.

Chemically speaking, the chemical reaction of the substances contained in coffee stops at the roasting stage. Coffee brewing is simply the physical extraction of chemical components produced during roasting. The extractability of different components depends on the solubility of the component, while the solubility of a substance depends on the polarity of the substance. Some atoms, such as oxygen, are more polar than others, such as carbon. When oxygen bonds to carbon atoms, the less polar carbon atoms are adsorbed around the oxygen atoms.

This combination of atoms, especially atoms of unequal polarity, results in molecules that are slightly polar. With this knowledge, let us return to solubility. In general, polar molecules in coffee are more soluble in water than polar molecules. This is because water molecules themselves are polar. The less polar hydrogen atoms are adsorbed by the more polar oxygen atoms, making the water molecules slightly polar. Therefore, water molecules react with other polar molecules around them, causing them to dissolve. It seems that the polar molecules in coffee are much more likely to be extracted than the polar molecules.

Many scientists want to know experimentally which soluble organic molecules make up coffee's aroma. Of the thousands of known chemical components, most are extracted during coffee brewing, but only a few make up coffee aroma. Other studies have found the concentration of aromatic substances needed to be detected by human olfactory organs. The percentage of coffee in which the concentration of aromatic substances can be detected is also known as the "odor activity value (OAV)". Scientists use this to measure coffee aroma content.

Coffee aroma is mainly composed of several types of substances. The most important of these is sulfur, such as 2-furfuryl sulfur. These substances contribute to what we commonly call the "ripe bean flavor" or "baked flavor." In addition, certain chemicals themselves cause certain negative odors. But it is these substances that interact with other substances to make subtle differences between the aromas of each coffee. Methanethiol, for example, usually causes a rotten cabbage smell and a mouth odor after flatulence; another sulfur substance, 3-sulfhydryl-3-methyltoluene sulfate, has a "cat smell" of its own.

In addition to the above substances, coffee is also rich in other kinds of aromatic substances, such as aldehydes, which bring fruit flavor and astringent flavor, furan, which brings caramel flavor, pyrazine, which brings dust flavor, etc. O-methoxyphenol and other phenolic substances bring smoke and spices. The aroma of coffee also contains pyrrole and thiophene, but due to the low concentration of both, the aroma is not obvious.

As scientists continue to study, we are constantly improving our understanding of coffee aroma. A 2008 study showed that coffee aroma affected genes and proteins in the brains of rabbits, making them feel more relaxed. Although the rabbit brain is different from the human brain, we can infer that it is not just the caffeine in coffee that can make you feel refreshed. Its aroma can also make you feel refreshed!