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Coffee roasting: How does it work?

Coffee roasting: How does it work?

 

Roasting coffee is the action of cooking, heating, toasting in order to transform the green coffee bean into a roasted coffee bean. The equipment that will be used for this cooking is called a roaster. If, in the past, families roasted their coffee themselves, this fundamental operation is now a matter for specialists. Today, the roaster, or master roaster, heats the green coffee bean in order to transform it into a brown bean made up of more than 800 aromatic molecules.

  • What is roasting used for?

Roasting is arguably the most important step in making coffee. The green beans have no aroma, but the heat will have several effects on the beans:

-They will lose some of their water and swell slightly;

-Their color will gradually change;

-The thermal decomposition of certain chemical compounds will help develop the aroma.

The result (i.e. the taste of the coffee) will however depend on the following parameters:

-The variety and geographical origin of the coffee; (altitude, type of soil, angle of the ground, sunshine, climate, humidity);

-The treatment conditions after harvest;

-The roasting;

-The final preparation.

Without roasting, none of these steps could achieve the aroma we know. this chemical chain transformation, roasting, was discovered by two chemists Maillard and Strecker.

  • Maillard’s chemical reaction

it is the interaction under the effect of heat, between the sugar and the acids naturally contained in coffee that will lead to caramelization. This caramelization is characterized by the change in pigmentation / color and has the effect of giving the coffee all its aromas.

  • Strecker’s degradation reaction

it is the chemical modification that cascades after the Maillard reaction. It releases CO2 and is responsible for the foam in the preparation of espresso version coffee, called crema.

  • Procedure

The heat of the oven must be between 180 ° C and 220 °C when the beans arrive. During this period, the master roaster analyzes and regulates the heat source according to the reactions of the coffee. The roaster’s responsibility is to determine the development of the roasting (time, temperature, air circulation, etc…). Often the roasting control is done automatically during the first 17 minutes. Once this quarter of an hour has passed, the roaster judges the result obtained using a viewing window and a probe with which he can take a few coffee beans. its visual, olfactory and auditory analysis allows it to assess the roasting. If it feels “ready,” he opens the metal roaster door to let the coffee beans flow into a cooling bin. blades and a powerful fan then come into action to quickly cool the grains. Without this step, the coffee beans would continue to heat up and the roasting would then exceed the desired level.

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