Coffee Roasting: From Bean to Cup

Roasting is one of the most fascinating aspects of the coffee industry, as it turns green coffee beans into gold in a cup in a matter of minutes.

When Fire Was Replaced by Modern Technology

There are countless legends about the discovery of coffee’s effects and its roasting. However, we cannot say with certainty when coffee was roasted for the first time or how it was actually roasted. We can only imagine how a group of curious bystanders gathered around a fire, where a few green coffee beans were roasting on a kind of stone slab. They gradually caramelized and browned until the first bean cracked and the air was filled with an sensational coffee aroma. At that moment it was clear to everyone that those otherwise inconspicuous green beans were actually a hidden treasure.

It’s been many years since coffee was first roasted. Early, primordial roasting methods where coffee beans roasted over hot coals using a perforated clay bowl with holes and handle gave way to innovative industrial-age designs. And it is about contemporary, modern roasting that we are going to talk about today.

Not Every Coffee Roasting Is the Same

Today, coffee roasteries use fully automated machines that would have blown the mind of more than one coffee lover half a century ago. We have invented and created sophisticated, computer-controlled equipment to make the relatively simple process of roasting coffee beans even more rigorous and precise.

However, even contemporary, modern coffee roasting can also be different. The commercial, large-scale roasting of commodity coffee has little in common with the craft roasting of specialty coffee. Since commodity coffee is mostly cheap, of lower quality and not particularly interesting in terms of taste, the technician responsible for its roasting usually pays no attention to developing flavours specific to a particular terroir or variety.

Craft Roasting of Specialty Coffee

However, specialty coffee roasteries take a different approach to roasting. For them, coffee roasting is a craft designed to bring out the innate aromatic and flavour qualities inherent in each coffee. Although there are professionaly trained roasters, who have learned the craft by trail and error, working in these coffee roasteries, they understand the coffee and the whole process of its roasting all the more.

There are dozens of specialty coffee roasteries in Slovakia alone, but each one has its own style and roasting philosophy. This is also why it is common for the same coffee to taste differently from different roasters. However, what all the roasteries of specialty coffee have in common is respect for coffee and its „genealogy“. Therefore, each coffee has its own specific recipe, which according to the roaster, should benefit from the best.

Roasting Coffee without a Roaster is Pointless

Although today the roasting process is controlled by computers and special software, the human factor is still irreplaceable. The roaster monitors the coffee throughout the roasting process, taking samples, checking the colour, shape, hardness and aroma of the beans, and adjusting the temperature, amount of air, drum speed and roasting time as needed. For example, when a given batch of green coffee has a slightly different moisture content, the roaster has to adjust its roasting accordingly.

The process of coffee roasting can also be influenced to a large extent by the weather, i.e. outside temperature, humidity or pressure. The roasting machine draws in air from the outside environment while the coffee is roasting. For example, if heated humid air enters the roasting chamber, it transfers heat faster than dry air, so the roaster has to watch the beans carefully to prevent them from burning. Conversely, if cold moist air enters the drum during roasting, it can prolong the entire roasting process. If coffee is roasted without the roaster’s expert supervision, it could be roasted poorly or unevenly.

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The roaster is responsible for the final taste of the coffee before the barista. By guiding the entire process and carefully controlling the roasting temperature and time, he can ensure that the three essential aspects of flavour – acidity, sweetness and bitterness – are beautifully balanced in the cup. Coffee roasting varies, of course, depending on the coffee and its recipe, the roasting machine, the roaster’s technique, as well as the environmental conditions. In general, however, it can be said that coffee roasting has its phases.

Individual Stages of Coffee Roasting

Before roasting, the roasting machine must be preheated to the desired temperature. The green coffee is then weighed and poured into the roasting drum, which rotates regularly during roasting. Beans are roasted using hot air for about 10 to 15 minutes depending on the recipe and profile of the coffee.

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In the first phase, known as the drying phase, the beans gradually reduce their size and weight as excess water evaporates from them. A high temperature in the drum is required to start the evaporation process. The initial 11-12 % moisture content of the beans gradually drops to about 2 %, which is why their appearance or aroma does not change during the first few minutes.

When the water evaporates from the beans, their colour slowly starts to change – this is called the yellowing phase, also known as the Maillard reaction. Even at this stage, the beans are still quite hard and their aroma is more reminiscent of rice or bread. Gradually, the beans begin to expand and the thin skins – popularly known as chaffs– separate from the beans under the influence of the air flow.

The third phase, so-called first crack, is characterized by the accumulation of steam and various gases, especially carbon dioxide, in the beans, subsequently leading to their rupture. The process is very similar to making popcorn – the coffee beans double in size while making a specific popping sound. From this point on, important chemical processes begin to take place in the beans that develop the familiar flavour and aromatic characteristics of coffee.

In the fourth phase, which we call the roast development, the roaster determines the resulting colour of the beans, their degree of roasting and therefore the resulting flavour. At this very moment, it can affect the balance between acidity, sweetness and bitterness. Mainly acidic and fruity notes emerge in light roasted coffees, sugars gradually dissolve in medium dark roasting, giving the coffee sweeter notes and the acidity begins to subside. When roasted dark, the caramel begins to turn bitter, which is manifested by notes from chocolate to tobacco. In the case of premium specialty coffee, this is the final and very important roasting stage, where even a few seconds can change the final taste of the coffee.

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There is a fifth stage, the second crack, used primarily for large commercial coffees. At this point, the oils rise to the surface of the beans, the acidity disappears completely and the coffee takes on a generic, bitter taste. For this type of dark roasting, the term „French roasting“ or „Italian roasting“ is used. For high quality specialty coffee, this degree of roasting is literally undesirable, as it causes the coffee to lose all its natural flavour characteristics. Although many coffee drinkers prefer this type of bold bitter flavour, a darker roast is more suited to coffee blends.

After roasting, the hot coffee beans are poured into the cooler, where they are cooled with cold air and constantly overturned by a mechanical arm. Cooling the beans quickly is particularly important to avoid over-roasting and other chemical processes that could affect the final taste of the coffee.

The freshly roasted coffee is then stored in special containers, where it is left to mature for several hours or days. Roasting produces carbon dioxide, which is released from the beans after about three hours, along with other aromatic substances. It takes about 12 hours for the coffee to reach its greatest, full-bodied aroma. This process is responsible for the pleasant aroma of roasted coffee.

Only after the coffee has „matured“ does it go to the packaging facilities, where it is packaged and distributed to customers. If the coffee is packed immediately after roasting, it could become „smothered“, so to speak, which would then again have a negative effect on its taste.

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