February 24, 2021

Let's Get Roasted!

By Scott Thomas
Image of unroasted beans being roasted while roasted beans are in the cooling tray of a commercial roaster

After processing and before roasting, all coffee beans start out as green beans and do not have much of a smell or taste.  Why you ask?  Green beans are insoluble, which means the flavor compounds are not accessible, until they are roasted.  Roasting makes the coffee bean soluble and creates the various flavors and aromas.

How do the roasters choose how light or dark to roast the green coffee beans?  And how do the roasts relate to flavor? 

Dark, medium, light roasts are just words and contain no magic.  The magic is created by the Roasters who test each batch of green coffee beans to find the best roast profile that produces the desired flavor and aroma.  Green coffee beans have different roast profiles based on where the bean was grown and how the bean was processed.  The roast profile is manipulated by time and temperature which is what creates the flavor.

Roasters can roast their coffee quickly at a lower temperature to create a lively or milder coffee, roast their coffee slowly at a higher temperature to create a mellower and sweeter coffee, and roast their coffee at much higher temperature to create chocolate or smoky tones.  The darker the roast the more bitterness is present. 

However, flavor is not the only characteristic of the different roasts.  The beans will look physically different as well. 

Light roasts will be a light brown color with no oil on the surface. A medium roast will be a medium brown color with no oil on the surface. The medium-dark roasts will be a dark brown color with some oil on the surface. Finally, the dark roasts will be black (maybe even charred) and oily.

There are several chemical reactions and stages of roasting … Maillard reaction, Caramelization, First crack, and Second crack. 

The Maillard reaction is basically the browning process (reaction between the amino acids and sugars) and adds a savory flavor to the bean.  Green coffee beans contain sugar and in the Caramelization reaction that sugar browns releasing acidic and aromatic compounds.  These compounds produce the perceived sweetness. 

Both reactions produce volatile gases and along with the water vapor and other gases cause the coffee bean to crack open to relieve the pressure.  This stage is called the First crack and sounds sort of like popcorn.  The Second crack happens as the beans continue to cook and is the sound of the bean breaking down.  At the Second crack the beans are normally a medium to medium-dark roast.  Further cooking produces your dark roasts, and the beans will continue to get darker and shinier and more bitter. 

Each roast profile is purely subjective.  You may like a light roast in one coffee and yet a dark roast in another. 

Why not share your thoughts and favorite roasts with us?

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