Mechanism of Melanoidin Formation During Roasting
During the heating of green coffee beans, a series of complex chemical reactions occur, most notably the Maillard reaction between reducing sugars and amine-containing compounds such as amino acids, peptides, or proteins. As roasting progresses, intermediate products of the Maillard reaction continue to polymerize, combining with polysaccharides and chlorogenic acids (CGA) to form high-molecular-weight, nitrogen-containing, dark brown compounds with complex network structures, known as melanoidins.
The presence of melanoidins not only determines the characteristic brown color of roasted coffee beans but is also the primary factor responsible for physical and chemical changes in the brew during extraction.
How Melanoidins Shape Body and Flavor Adherence
When tasting coffee, body or mouthfeel is one of the most important criteria for assessing quality. Body is not only measured by the concentration of total dissolved solids (TDS) but is also strongly influenced by the structure of molecules present in the extract.
Melanoidins are high-molecular-weight compounds. When dissolved in water during brewing, their bulky polymer structure significantly increases the viscosity of the solution. This viscosity creates a thick, smooth sensation and lasting mouth-coating after drinking, helping the coffee's aftertaste become deeper and more rounded.
The Link Between Melanoidins and Crema Stability
The espresso extraction method uses hot water under extremely high pressure (typically 9 bar or higher) forced through finely ground coffee. This pressure not only dissolves small-molecule compounds but also releases and emulsifies a large amount of fats (coffee oils) along with CO2 bubbles, creating the characteristic foam layer known as crema.
However, if only oil and water were present, this foam would quickly break and dissipate due to surface tension. At this point, melanoidin compounds act as natural surfactants. Thanks to their special amphiphilic structure, melanoidins envelop emulsified oil droplets and CO2 bubbles, preventing them from coalescing. The tight binding between oil, gas, and the melanoidin polymer network reinforces structural integrity, keeping the crema smooth and long-lasting, and shaping the thick body characteristic of a standard espresso cup.