Every morning we enjoy our delicious cup of coffee, almost as a ritual, something automatic, without stopping to think, "How did this cup get into my hands?" Well, in recent years it's true that coffee culture has spread a bit more and knowledge about coffee has increased. More and more people know where it comes from, what types of coffee we can find on the market, and that a fresh roast is important… but ah, my friend, we know it's roasted, but how is it roasted? And how does the roast affect the flavor?
Here's one of the many critical points that coffee goes through on its journey to the cup to achieve that incredible and pleasant flavor. First of all, we need to revisit the basic physics of heat transfer, since roasting coffee beans requires heating them. There are three ways to heat a material, in this case, the coffee bean:
- By convection, we heat air, we circulate this hot air among the coffee beans and they absorb the temperature, thus roasting them. A clear example of this system is when we put the oven in fan or convection mode.
- By contact, we heat a surface, in this case the walls of the drum where the coffee beans are, and when the bean rests on the hot wall of the drum it absorbs the heat, thus roasting the beans, an example is a frying pan.
- By radiation, electromagnetic waves emitted by a hot body or created by heat transfer the heat to the coffee bean, causing it to heat up and roast; an example would be a microwave.
The most common methods for roasting coffee are convection and contact. Some machines heat the walls of the drum with a burner, which then heats the coffee by contact. Others have a separate combustion chamber that heats the air, which is then circulated through the drum, roasting the coffee by convection. Radiation roasting is a feature found in very few roasters on the market. The final cup result is neither better nor worse depending on the roaster's method; it simply has subtle variations that depend on the roaster's preferences. They may value one roasting system more than another.
Another thing to keep in mind is that coffee is never roasted using a single method. Convection roasters also heat the drum, and there's a small percentage of heat transfer by contact. The accumulated heat from the beans creates electromagnetic waves that transfer heat to the surrounding beans, so there's also some radiation involved. However, these roasters are considered to primarily roast by convection. The same applies to contact roasters; they heat the air circulating in the drum, and there's a small percentage of heat transfer by convection and radiation, as in the previous case. But these are also considered primarily contact roasters.
Now that we know how coffee is roasted, it's time to delve into the complex world of brewing coffee to develop its flavors. Besides varying the flavor by changing the roasting recipe—for example, a high-heat initial roast is very different from a low-heat one—we can also speed up or slow down the final roasting phase. One aspect of the recipe we can identify and choose is whether we want a light, medium, or dark roast. And the million-dollar question: how will this affect the final result in the cup?
Yes, the flavor does change, quite a bit. Sensory-wise, we can identify enzymatic notes in coffee (flowers, seeds, herbs, etc.), sweet or caramelized notes (honey, caramel, cane sugar, etc.), and roasted notes (nuts, cocoa, etc.), and finally, defects (smoky, ashy, medicinal, or chemical notes, etc.). Well, when we roast coffee and develop its flavors, we first develop the enzymatic notes, then the caramelized ones, then the roasted ones, and finally the defects. But we also have the problem that as we progress through the roasting process, we also destroy its properties in that order. Therefore, in three different roasts, with the same coffee, we will find:
- Light roast: the coffee will be the most acidic of the three roasts, with herbal and floral notes, few or almost no notes of nuts and very few caramelized notes.
- Medium roast: the acidity is slightly reduced, enzymatic notes are lost, especially herbal and floral ones, but not all; we gain sweetness and caramel and fruity notes, and the nutty and cocoa notes from the dark roasts appear more strongly.
- Dark roast: the enzymatic notes have completely disappeared, as well as the acidity is now scarce or nonexistent, the fruity notes disappear a little, but the caramelized ones are retained, the toasted notes appear strongly, especially of toasted nuts and some carbonation notes may appear due to the high roasting.
So, which one should you choose? Above all, it depends on your preferences and tastes. A medium roast is always the most well-rounded and suitable for everything. But if you're a fan of acidic coffees, of that pronounced citrus acidity, then a light roast is the way to go. Conversely, if you're a fan of Italian espresso, with its full body, lack of acidity, and pronounced nutty notes, then you'll opt for a dark roast. You can also choose based on the occasion or how you'll be using the coffee. For example, a morning latte calls for a dark roast that highlights the coffee over the milk and gives you a sweet drink, so a dark roast is definitely the way to go. But if you're going to make a filter coffee and want the coffee to express all those complex nuances that develop in the cherry, then a light roast is the way to go. And if you're going to use it for both brewing methods, filter and latte, then a medium roast is the way to go.
The best choice? Try different roasts of the same coffee and experiment, learn, play with coffee, which is what hooks us so much about the world of coffee.
