Why is coffee roasted?

Roasting is an essential coffee process that goes beyond the simple extraction of flavors and aromas; it involves the application of carefully controlled heat to trigger a series of chemical reactions that shape the character and quality of the coffee.

It is important to understand the origin of the verb “to roast“, which comes from the Latin “torrefacere” and translates as “to dry”. This notion of drying is key to understanding the essence of coffee roasting.

Through this article, I will clear up any doubts you may have about why roasting coffee is a vital practice in its preparation.

What happens when coffee is roasted?

When coffee is in its natural state, i.e., green, it does not have the characteristic flavor and aroma that we associate with it. In addition, green beans are too dense, elastic, humid, and resistant to pressure, which makes it impossible to grind them and extract the essence of the coffee.

Even if it could be extracted at this stage, the resulting beverage would have unpleasant overtones with unattractive herbaceous characteristics. Therefore, the roasting stage is very important.

It is important to keep in mind that the roasting process helps to:

  1. Develop aromatic compounds: During roasting, sugars and amino acids in coffee beans interact and combine, generating a wide range of aromatic compounds. These compounds are responsible for the different flavor profiles and the exquisite aromas that we find in the cup.
  2. Expansion and caramelization: In this process, the internal moisture of the bean is converted into steam and exerts pressure, causing the bean to increase in size. In addition, the sugars in the beans caramelize, which contributes to the formation of sweet and roasted flavors in the coffee.
  3. Degassing: During roasting, the coffee beans release carbon dioxide and other gases that have accumulated in their interior.

Physical and chemical changes of coffee during the roasting process

During the roasting process, coffee undergoes a series of physical and chemical changes fundamental to obtaining the beverage we enjoy. These changes include:

  • Increase in volume: When coffee is subjected to heat, the internal humidity is converted into vapor, which causes an increase in the size and volume of the beans.
  • Weight loss: Roasting causes the evaporation of moisture and the decomposition of the organic compounds present in the coffee. This leads to a reduction in the total weight of roasted beans compared to green beans.
  • Change in density: Roasted coffee beans are usually less dense than green beans.
  • Flavor development: During roasting, the chemical compounds in the beans react with each other and are transformed into coffee’s characteristic flavors and aromas.

Adequate roasting allows the coffee beans to crumble easily and to be ground. This step allows the grind to have greater contact with the hot water.

The phases of the roasting process

The coffee roasting process consists of three main phases that are fundamental for achieving the desired characteristics in the beans:

  1. Drying phase: In this stage, the green coffee is subjected to heat to eliminate the moisture in the coffee beans almost completely.
  2. Color change phase: The coffee beans absorb heat from the environment during this phase. This is where a notable transformation occurs, as the beans change color, going from green to darker tones, such as brown.
  3. Development phase: A key event known as the “first crackle” occurs in this final stage. This crackle is a distinctive sound that occurs when the internal pressure of the kernel increases and releases accumulated steam and gases.

Decisive factors in roasting: time and temperature

Time and temperature are crucial elements in the coffee roasting process since they directly influence the quality and aromatic profiles obtained. It is necessary to find the optimum point to obtain the desired results.

A dark roast is a product of too high temperatures or an incorrect time and can produce a bitter and unpleasant taste in the cup. On the other hand, if the roasting is too light, this indicates that the coffee has not yet reached its maximum aromatic potential.

The medium roast is where all the aromas of quality green coffees can be brought out to the maximum. It is the optimum point to obtain a cup of coffee with balanced and complex flavors.

Note: When roasters work with low-quality beans, they opt for a dark roast instead of a medium roast. This is because dark roasting hides the defects present in the coffee. However, when a meticulous selection of each bean is made, the roaster does not need to resort to these concealing practices.


During roasting, chemical reactions that develop aromatic compounds are triggered, which contribute to the expansion and caramelization of the beans, allowing the liberation of accumulated gases.

In this process, the coffee undergoes physical and chemical changes, such as an increase in volume, loss of weight, and a change in density.

Adequate roasting facilitates grinding and the complete extraction of the desired flavors and aromas. The process consists of drying, color change, and development phases, and time and temperature are crucial factors in obtaining balanced aromatic profiles.

Written by Pablo Barrantes Nevado
I am Pablo Barrantes, a coffee lover. I decided to start this website to solve all the doubts that arise every day when preparing our favorite drink: coffee. I am an industrial engineer by profession, but I have worked in coffee shops for many years, where I have learned all the secrets about coffee machines and coffee. My passion for coffee has led me to investigate and study beyond the obvious, and thanks to this, I can offer solutions and give news about coffee and coffee makers. I hope you enjoy reading as much as I research, document and write here.

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