Roasting coffee: the different phases and the development of the coffee bean

Here at Café du Jour we have a large selection of freshly roasted coffee. The flavour of a coffee is largely decided by its roast profile: the speed of roasting in the different phases and the moment we take the beans out of the roaster. But which phases does a coffee bean go through during roasting?

Unroasted coffee beans, as we receive them

The unroasted coffee beans (actually the seeds of the coffee cherry, without the skin) arrive here from the country where the coffee was produced. Most of our coffee beans enter Europe through the port of Antwerp and arrive in jute bags of around 70 kg each. In the end, one bag gives us around 57 kg of roasted coffee beans, because the beans lose between 18% and 22% of their weight in moisture during roasting.

These green beans are very hard, smell a bit like grass and are very compact.

The drying phase: most of the moisture evaporates

In this phase we gently warm the beans. There is a clear difference between warming the beans and heating them: in this phase the beans must not get too hot yet. The maximum temperature of the beans is about 150℃. The drying phase takes about 4 to 8 minutes and makes sure the beans are properly dry. There is no flavour development yet; that comes in a later phase.

The 'yellow' phase: coffee beans that smell like hay

This phase marks the beginning of the real roasting process: the Maillard reaction takes place. This is a complex series of reactions between reducing sugars and amino acids under the influence of heat, and it is what makes the coffee change colour. Even though the drying phase comes first, not all the moisture is out of the beans yet, so drying continues through this phase.

During this phase the coffee smells a bit like rice and hay. The hot air coming out of the roaster is more steam than smoke.

The 'yellow/brown' phase: the smell of baked bread

We are now at the end of the preparation for the actual development phase. The coffee is starting to smell like baked bread. We use this precise moment to moderate the temperature in the roaster, so we don't move too fast through the following phases. The master roaster now optimises the ratio between airflow and heat in the roaster. Depending on the type of coffee, this ratio can be different every time. From now on less moisture escapes, and the smoke needs to be extracted constantly.

The 'first crack': where flavour development begins

During the drying phase and the yellow/brown phase the coffee beans have absorbed energy. Now the roast turns exothermic and the coffee enters its first 'crack': the stored energy makes the beans burst open. The beans are small, so each burst is tiny, but because there are hundreds of thousands of beans in the roaster at once (one cup of coffee is about 70-80 coffee beans), this creates an audible cracking noise. That is why we call it the first crack. It marks the start of the development phase and of the coffee's flavour development.

The development phase: light to medium

Some blends and single-origin coffees are taken out of the roaster in this phase

The development phase is now fully under way. Depending on the roast profile we want and the coffee we want to make, it is time to decide when to take the beans out of the roaster. For light to medium roasted beans, the development phase is normally around 15%-20% of the total roasting time. In this phase the coffee is a bit more fruity and more acidic than bitter. Coffee taken out of the roaster in this phase has a distinct character of its own, which makes it easier to taste the difference between types of beans.

The development phase: medium to dark (the second crack)

Typical espresso coffees are taken out in this phase

Coffee that is roasted longer is more bitter. Most Italian brands, for example, are roasted longer than most other coffees. The longer we roast the coffee, the stronger the bitterness. The roast profile, the speed we are aiming for, is crucial in this phase because it determines the flavour. The coffee we call 'espresso' is usually roasted a little slower, but to a dark point. This makes it lose its fruity and acidic notes. Caffè crema is a coffee we want to keep a little more fruity, so we roast it faster with more heat. Of course, this differs per coffee bean, which is why developing a new coffee is a matter of trial and error, adjusting and adapting. During this phase the coffee 'cracks' for the second time.

The extremely dark phase

We rarely roast beans to this point, unless a customer asks us for a specific very dark roast

This coffee is usually not sold in supermarkets; even a pack labelled 'dark roast' is roasted lighter than these beans. The reason is that bean-to-cup coffee machines cannot handle such dark coffee. Very dark beans are oily on the surface, which can clog the machine and cause damage. We roast these beans only on request.

Which roast to choose, and creating your own roast

We can roast coffee exactly to your liking (from 2 kg). Our range is never roasted more than four weeks before we ship it. We also sell unroasted beans for coffee lovers who want to experiment with roasting themselves, and if you want to go a step further, Café du Jour sells coffee roasters for home use.

Video of our coffee roastery

To give you an impression of the roasting process, we made a video in our roastery.