Let’s talk about roasting. All you need to do is roast the green raw coffee until it goes brown. It doesn’t sound any more complicated than frying up a burger. But it certainly is! Coffee roasting is based on a science about which entire books have been written. How great a coffee is depends on how its roasted. There are three main methods that are used to heat the beans: direct contact, hot air or radiation.
Classic drum or centrifugal roasters heat up the raw coffee by passing on the heat from its walls to the beans by direct contact also known as conduction. In this process, the coffee is kept moving with a paddle or by rotating the drum so that the beans are roasted as evenly as possible. However, in many roasters, hot air is also added in order to achieve a more homogeneous result. Here, the beans are roasted by convection.
Tangential roasters, roast the beans using hot air and have a clear advantage: the movement by mechanical paddle and the additional flow of air keep the beans moving, meaning that they have hardly any chance of burning on the surface. And when we say surface, we mean the surface of the beans themselves. The heat given off by the beans can cause them to continue roasting after the roasting process itself has ended. To prevent this, they are cooled with water to stop this further roasting. Unfortunately, many industrial coffee roasters take advantage of this: they use this water to return the weight that the beans lose during the roasting process, which dramatically affects the flavor of the coffee.
Now we know how the beans are roasted, but what actually happens to them? Quite a lot, both externally and internally. They lose a full 17% of their weight – but they also grow in size. The weight loss is mainly caused by the water vapor being released.
When the bean has absorbed enough heat, its amino acids and sugar start to react with one another, which triggers a real flavor explosion. It is this reaction that creates the characteristic aroma profile of each bean.
The taste of the coffee ultimately depends on two factors: the roasting time and the temperature. These two factors determine the roast – the color and flavor – of the bean. As we all know, taste is very subjective, but everyone can agree that a light roast contains more fruity and floral aromas and tends to be more acidic, a medium roast is balanced, has more complex aromas and has only a mild acidity, whereas a dark roast has little acidity but strong roasted aromas and a strong body.
Appearances can, however, be deceptive. Poor-quality mass-produced coffee is often subjected to a quick roasting process: the beans appear dark on the outside, but are usually still green on the inside. This type of roasting doesn’t just create coffee that tastes awful, it is also responsible for coffee’s reputation for being bad for the stomach. The chlorogenic acid, a suitably horrible name for the substance that causes these stomach problems – is only removed from the coffee beans when they are carefully roasted for a longer period of time. And this is precisely what we do.
As surprising as it may sound, this is only a brief introduction to the complicated art of coffee roasting. To sum up: no, coffee roasting is absolutely nothing like frying up a burger.