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Coffee Roasting - From Green Bean to Roasted Bean

Updated: Nov 18, 2023

So you drink coffee, but have you ever seen a coffee roaster in action? Do you understand how coffee roasting works?

The roaster in the clip above is a drum roaster.

In simplistic terms, roasting of coffee is completed with various styles of equipment which all have one thing in common- heat, and lots of it. All styles of roasters have an adequate amount of heat, airflow, and allow movement of the beans.

The roast profile varies based on the batch size, the type of roaster used, type of roasting method, how heat is applied, when heat is applied, and length of roasting. Regardless of all of those factors, the stages of roasting are consistent.

The first stage is the drying stage where moisture from the bean evaporates.

The second stage is called the yellowing stage and is when browning of the coffee begins. During this time the beans begin to expand in size and the chaff, a thin layer of skin, begins to flake off and is separated from the coffee bean.

The third stage is what is called the “first crack”. This stage is signaled by an audible sound, to be compared to the sound of popcorn popping. The sound is produced by a chemical reaction of gasses causing the bean to break open and increasing the size of the bean to almost double.

The fourth stage is roast development. This is when the coffee bean roast level is declared. As you may assume, ending this stage early provides a lighter roasted coffee than a longer roasting time providing a dark roast. If another popping noise, more of a snap, begins to occur that signifies a “second crack” which brings the coffee to a darker roast.

Notecard with coffee beans from green bean to dark roasted beans.

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