How do coffee beans change during roasting?

During roasting, the coffee bean undergoes a transformation, which can be perceived through several indicators.

In short, here are the 3 things you need to know:

1. Smell control. We’ll know that roasting has begun the moment the coffee beans start to smoke and release their aroma.
2. Colour variation. This parameter is mainly influenced by the degree of roast. Raw coffee, which is initially green in colour, as roasting begins, starts to take on a broad range of colours varying from light brown to very dark brown. Colour plays a fundamental role in determining the organoleptic characteristics of the drink, including: acidity, bitterness, sweetness, aromatic intensity and body.
3. Increase in volume. During the roasting process, the coffee bean changes in size. In this phase, the so-called “first crack” occurs, a process that is almost imperceptible during a standard roast, during which the beans rotate inside the roaster. Seen up close, the first crack allows us to witness the explosion and cellular expansion of the bean. After the bean’s development time, the roast is stopped at a “medium roast” colour with a 14% loss of weight in the bean, while the bean’s size increases by around 50%. From the first crack onwards, what happens is the caramelisation of simple sugars, which can continue up to the second crack.

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Once the desired level of roast has been reached, the coffee must be immediately cooled to prevent combustion from continuing. At the end of the process, the coffee is left to rest in dedicated containers called “silos”, before being packaged and made ready for sale.

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