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The different coffee roasting methods

Coffee roasting – it can’t be that difficult. If only you knew ...

All you need to do is roast the green raw coffee until it goes brown. It doesn’t sound any more complicated than frying a hamburger. But it certainly is! Coffee roasting is based on a science about which entire books have been written.


Clean cultivation, correct harvesting, the best processing – the raw coffee is crucial for the quality of the bean. But it is during the roasting process that the specific characteristics of the coffee are brought out – or completely destroyed. How great a coffee really is depends above all on how it is roasted.

Roasting over fire – the good old days

The first requirement for roasting? Easy: the roaster. And nowadays there are many of them. The times in which coffee was tossed in a cast-iron pan over a fire are long gone – except in Ethiopia. But coffee is roasted on a much larger scale in the rest of the world.

There are three main methods that are used to heat the beans: direct contact, hot air or radiation. But here, as with many things in life, getting the right blend is also crucial – the challenge is to heat up the beans evenly. After all, nobody wants burnt beans.


The two Cs: convention and conduction

Classic drum or centrifugal roasters heat up the raw coffee by passing on the heat from its walls to the beans by direct contact, or 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.

Overheated, overwatered, overpriced?

Tangential roasters, which we also use, 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 don’t just mean the walls of the roasters, but 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 flavour of the coffee. This is why we ensure that our beans have a water content of no more than 2.6 per cent. In their natural state, the beans contain 1.9 per cent water. Regrettably, up to 5 per cent residual moisture is allowed by law.


When the beans work up a sweat

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 vapour being released.

The Maillard reaction is probably the most complex process. When the bean has absorbed enough heat, its amino acids and sugar start to react with one another, which triggers a real flavour explosion. It is this reaction that creates the characteristic aroma profile of each bean, which theoretically can consist of up to 1,000 aromatic substances.

The roast reveals a lot – but not everything

The ultimate taste of the coffee ultimately depends on two factors: the roasting time and the temperature. These two factors determine the roast – the colour and flavour – 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.

A science in its own right

As surprising as it may sound, this is only a brief introduction to the complicated art of coffee roasting. Dozens of books have been written about this subject, and there are at least as many different opinions as to which method is the best. It is no coincidence that the person who decides whether the finished coffee is good enough is called a master coffee roaster rather than just a coffee roaster. To sum up: no, coffee roasting is absolutely nothing like frying hamburgers.