ROASTING coffee beans: do you know that the roasting process gives the coffee beans their smell, color, and taste. Roasting is the process of toasting coffee to develop its aroma.
We’ll take a look at:
Roasting coffee beans techniques
In traditional techniques, heat is transmitted through a metallic surface that is said to be conductive. In the beginning, the appliances were very rudimentary: frying pans or plates on which the coffee beans were placed. They had to be stirred very often until they were toasted on all sides. Then they invented rotating drum machines that were rotated over a heat source, which were gradually perfected.
The technique of direct heating (without the use of a conductive surface) only appeared at the beginning of the 20th century. It consists of sending hot air directly onto the coffee beans. The hot air evenly toasts the beans.
To control the quality, specialists taste the freshly roasted coffee beans every day.
During the roasting process, the coffee acquires its characteristic color, delicious aroma, and flavor thanks to a device called a “roaster” which is heated to a temperature of 180 to 200° C.
The roasting coffee beans process lasts from 12 to 20 minutes depending on the desired color. During the work, samples are taken with a probe to check the progress of the operations and the degree of roasting. With the naked eye and optical instruments, these samples are compared with the previously established model. All beans must be roasted ‘through’.
Once roasting is complete, the beans are emptied onto a cylinder called a ‘cooler’ and cooled, usually with air, but sometimes also with water.
Depending on the quality, the coffees are blended before or after roasting to preserve all their original characteristics.
The different roasting intensities
Depending on countries, regions, and tastes, the color of roasted coffee varies with increasing intensity from North to South. Thus, we can distinguish :
- light roasting (blond)
- medium roast (amber)
- medium roasting (monk’s robe)
- deep roasting (brown)
- very deep roasting (very brown)
The changes in the color of the coffee beans
The main purpose of roasting is to develop the aromas. The transition from green coffee to roasted coffee involves a series of chemical and physical reactions.
At around 190°, the temperature of the beans, as measured by an electronic probe, the coffee must be taken out and cooled down quickly as the internal combustion continues. The coffee produces its heat with the release of CO2 inside the bean cells. At this point, their color changes to dark brown. They then give off an exquisite smell. This moment is crucial. Roasting must not be continued, otherwise, the coffee will burn. It must, therefore, be cooled immediately, on a sieve. The cooled coffee is then sorted in a de-stoner, which separates the good beans from the undesirable residues that are heavier than the beans.
Chemical reactions after evaporation of water
- Transformation of sugars that volatilize and turn into aromas (Maillard reactions).
- Formation of aromatic compounds and volatile acids from the sugars contained in green coffee.
- Destruction of certain constituents, such as tannin, fibers, and chlorogenic acids.
These chemical transformations will produce physical reactions:
- Change of color (Stucker reaction)
- Increase in volume under the effect of heat (about 60%)
- Weight loss (about 20%) by evaporation of water.
Artisan roasters still use limited capacity equipment that roasts coffee in twelve to fifteen minutes. The amount of coffee roasted at one time in the roaster is called a “spit”. The limited capacity means that the coffee has to be roasted daily so that the coffee is always freshly roasted and the origins can be captured. Industrialists are nowadays equipped with high-capacity equipment that roasts almost permanently in an automated way either by spit or on continuous hot air beds. This equipment roasts much faster.