Chemical Changes During Coffee Roasting

Vietnamese Coffee Exporter

As coffee beans transform in the roaster’s heat, hundreds of chemical reactions will continuously occur. Some compounds will decompose, some will be turned into other compounds, and countless new combinations are formed, all of which, plus a series of physical transformations, will begin in the coffee nucleus. Unique taste. Let’s learn about Chemical changes during coffee roasting with Helena.

In chemical language, every coffee-related reaction in a roaster is attributed to a process called endothermically. These transformations occur when organic material reaches a decomposition temperature, which produces volatile compounds and leaves carbon remnants (aka coal). During coffee roasting, we set a limit to avoid making coffee beans coal, but enough for them to undergo chemical changes caused by thermolysin to form flavour compounds.

Maillard reaction

Maillard is not just one but a series of chemical reactions that are crucial to creating the characteristic and brown flavor of roasted coffee. The responses are called after Louis Camille Maillard, a French physician who reported them for the first time in 1910. This process begins in the roasting oven between 140°C and 160°C; as the temperature reaches 170°C, caramelized reactions start to occur, burning all of the remaining sugar.

Between decreasing sugar and amino acids, the Maillard reaction occurs. Any sugar with a free aldehyde or ketone group is referred to be a detour. These groups link carbon chains with a double bond through an oxygen atom, efficiently reacting with amino acids and other molecules.


There are countless pathways to the Maillard reaction that occur in coffee beans, with (n) amino acids and (n) sugars, then we will have n.2 Different flavor compounds. The most familiar of these products are roasted flavors toast. The Maillard reaction components can combine with other free amino acids to generate  Melanoidin. This dark brown substance is roasted, malty, bitter, and notorious. It plays a crucial role in producing and maintaining crema in espresso, giving your coffee cup a rich flavor.

Caramelized reaction

Unlike Maillard reactions, caramelization is a form of thermolysin that occurs at about 170°C (338°F). High temperatures will cause long, complex carbohydrate circuits to break up into hundreds of new, more minor compounds that add a significant amount of bitterness, sourness, scent. This reaction will continue until the roasting process is completed, and it also adds to the sweet aromas in coffee, such as caramel, toast, almonds, etc.

In addition, it should also be noted that the content of sucrose gives the sweetness the richness of coffee after roasting and affects acidity (acidity) since the caramelization reaction of Sucrose sugar will produce acetic acid. Therefore, we encourage coffee growers to harvest excellent ripening fruit with the highest possible sugar content to provide abundant raw materials for the Maillard & Caramel reaction group.

According to Scott Rao, dark roasting will break down over 99 percent of the county’s intrinsic sucrose intake, whereas pepper roasts would decrease by approximately 87 percent.

The breakdown of acid

Although many coffee drinkers claim that acid makes coffee more bitter or unpleasant, acid-free coffee is actually “hollow” and dull. One can experience cold brew coffee to minimize the acid content in the cup. But that almost necrotized the effort to balance the incredibly difficult acidity of the roasting process.

And when it comes to acidity, we can’t fail to mention chlorogenic acid (CGA), which is by far the most common acid in raw coffee beans, at 6%-8% of the CGA content in coffee beans which is higher than in any other plant. The roasting process will continuously break down the CGA depending on the temperature and time. 50% of the CGA will be lost when light roast and leave only 20% in the dark roast.

The formation of flavor compounds

How much of the soluble substance is in a coffee bean?

According to Scott Rao, about one-third of the volume of coffee after roasting is water-soluble. Meanwhile, the optimal extraction rate is about 19%-22%, which is equivalent to about 55%-60% of the total soluble substances present in coffee (since we limit the solubility of unwanted flavors in the cup), plus a small number of lipids and fragments of crumbled cellulose (also known as fines). These soluble substances, plus rich aromas, come from one of the following variations.

Volatile compounds

The new “coffee fragrance” takes shape a few minutes after the roasting process begins – the rapid growth of volatile aroma components happens when the coffee’s humidity falls below 5%. Then the caramelization and Maillard reactions, as well as the degradation and metabolism of amino acids, sugars, phenolic acids, and lipids, will jointly contribute to the development of aromatic compounds, including:

  • Aldehydes, the scent of blue fruits
  • Furans, contributing to the smell of caramel
  • Pyrazines, which smells of earth
  • Guaiacol smells of smoke, spicy
  • Sulfur-containing compounds like 2-furfurylthiol make up the characteristic aroma that we call “coffee roasted coffee,” but others don’t smell attractive — methanethiol, for example, smells like rotten cabbage.
Coffee will gradually lose its aroma during storage and use

Although CO2 is a volatile compound that does not contribute to the scent, it plays an essential role in coffee’s body coffee in general. It makes up the Crema layer in espresso in particular.

It should be noted that the aromatherapy content will peak at light to medium roast. The temperature will destroy the aromas created by it, leaving a spicy and smoky smell. At the same time, from dark roasting onwards, cellulose structures are weaker and more porous, and the ability to hold the aroma will be less than lighter roasting.

Non-volatile compounds

Some of these compounds are formed, changing during roasting, while others remain stable throughout the process. Most non-volatile compounds contribute to the flavor of the coffee. For example, caffeine, which is responsible for bitterness, sucrose for sweetness, and lipids for a sense of body, acids or melanoidin compounds formed in the Maillard reaction, also belong to the non-volatile group.

Chemical changes during coffee roasting

Speaking of caffeine, despite the general notion, darker roasting only reduces the volume of coffee beans due to dehydration, not reduces the caffeine content in the seeds (because caffeine is stable at a higher temperature than roasting temperature). Therefore, the more caffeine/weight, the ratio will increase, so with the same amount of coffee, the higher the roasted type, the higher the caffeine content.