Why are coffee beans roasted?

Fri 24th May 2019

In short, coffee beans are roasted so that they become coffee as we know it. Without the roasting process they are merely but a bean. Granted, that bean does possess all those unique qualities we associate with coffee but the flavour is non-existent until it is roasted.


Coffee beans are not actually beans. They are in fact the seedlings of a red or purple fruit, similar to that of a cherry, from a certain coffee species. Coffee beans are only referred to as beans due to their appearance and resemblance of a traditional bean. The raw coffee bean is green in colour and appears fresh.

There are two main types of coffee bean: Arabica and Robusta. Do you know the difference? Typically, (although not always!) Arabica coffee beans are higher quality, contain less caffeine and tend to be more fragrant with more flavours than the Robusta coffee bean.


From the young green bean to the glossy brown bean we’re all familiar with, coffee beans go through a rigorous transformation process when roasting, altering both the physical and chemical make-up of the coffee bean.

Coffee beans are roasted to extract the bean’s truest flavours. However, the coffee roasting processes are unique, complex and often tailored to produce the roaster’s own preference. Varying the timeframes and temperatures of the roasts, allow roaster’s to meet the needs of many different flavour pallets.


The art of roasting coffee beans is subjective, to an extent. There are varying methods but all are judged by the final flavour extracted from the humble coffee bean itself. A lot of the methodology for roasting coffee beans surrounds the length of time you heat (roast) them for, dictating the overall colour and taste.

Although state-of-the-art coffee roasting the equipment and facilities can give you an advantage, it is the knowledge of coffee that is the true art form. Each stage can determine a different outcome, depending on your intention, therefore use of the senses and experience is necessary.

Understanding the origin of the coffee bean, the processes of roasting and recognising the behaviour of the beans throughout the coffee roasting stages can often be coffee roaster’s most powerful tool.



Away from the expertise of an individual and modern technologies, there is a matter of science behind the roasting of coffee beans. It is this science which must take place, in order for coffee to become coffee.

Roasted coffee can be divided into two groups: volatile and non-volatile. The volatile components contribute mainly to the aroma, whilst the non-volatile elements attribute for the flavours we associate to coffee, such as sourness or bitterness (often determined by caffeine levels).

Throughout the roasting process, the coffee bean goes through a number of endothermic and exothermic reactions. In the endothermic phase, energy is absorbed in the form of heat; it’s at this point that the coffee beans lose their moisture, alter in colour and release bread-like aromas.

The exothermic phase sees energy being released in the form of heat, (in this case, steam). Once the moisture in the coffee bean has evaporated, it escapes the bean by rupturing it, causing it to crack or pop. By now the coffee bean has begun to develop its true flavours and aromas, as well as inheriting the rich brown colour we all recognise.

Finally, carbon dioxide begins to build causing a pyrolytic reaction. Another loud crack occurs, signalling the time for the rapid cooling phase. This is often done via the use of fresh air or water, to prevent any further exothermic activity and seal in their fresh flavours.


Tom Altoft – Roasting Expert

Technically, coffee can not become coffee without completing the roasting process. So, in answer to the question ‘why are coffee beans roasted?’ it’s quite simple. As highlighted in the article above, the coffee bean must undergo several roasting processes in order to become the product we all know and love, otherwise it’s fairly useless.

Moreover, the answer to the question could be to do with an individual’s love affair with the art and science behind the processes. It could also be answered by stating that the demand for coffee is on the rise, therefore the coffee beans must be roasted to supply the demand.

Either way, we’re just glad that someone back in the 15th century decided to drop a few into a pan above some flames and experiment.

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