In the lab

Slow roast... but not that slow

| 2019-04-09

It is often said about handcraft roasting that slowest the roast is, better the coffee is. It is true that roasting time is one of the main differences between industrial and handcrafting roasting. Industrial roasting can be done in 90 seconds, so to be honest, this let us a lot of room to make it longer. Semi industrial roasting is done between 7 & 8 minutes. The handcraft roast, also called artisan, takes at least 10 minutes. Having said this, there is also a myth… some might think that more time your coffee roasts and the best it would be. Well, it is false. A roast that lasts between 25 up to 40 minutes will not produce anything nice from your coffee. And this, even if you try that harder and harder!! An extremely slow roast is more likely to kill the profile of your coffee and will definitely produce a “baked” taste. “Baked” taste is not easy to explain, some say it is like heating a meat in a microwave. If we had to explain a murder, we would first try to understand who is - or was - the victim. Put it in other words, we are going to explain what a roasting profile is. When you put your coffee into the roaster, the roaster has a high temerature - around 200°C in the drum. Contrary to your roaster, you have around 20°C for your small grain. Once the coffee arrives into the roaster, its temperature is rocketing and the roaster temperature is, on the contrary, decreasing. In a determinate moment, your coffee and your roaster reach the same temperature. For technical purposes, we will call this moment the balance point.


This temperature (of grain), from the beginning till the end, would be known as the grain temperature, and would design your roasting curve This curve, would do but increase from the balance point until the end of the roast (or at least it should!!), just as it is shown on the graphic below:


The main risk by doing a too slow roasting is that your curve would stop increasing in temperature, making it roars or even decrease in temperature. Graphically (as in a hospital), a curve like this would kill the profile of your coffee and produce the famous baked taste on your cup! This curve would look like this: roster#3

If your curve looks like that, without any doubt, you could say that you have slowly killed your coffee. You need to take your time & care when roasting your coffee, but that doesn’t mean (or shouldn’t) leaving your coffee baking, as if you were cooking a smoked rump!! Take the time to know & control all the elements having an incidence in how your coffee roasts: what is its density? What about its humidity? What are the temperatures that you normally use for « this » or « that » coffee? Is your roasting atmosphere adequate to roast (isolated, good light, etc.) properly? And above all, the most important… cup always your coffees after roast (in different time intervals), if the results are good enough for you, save all your roasting parameters in order to be performing and have standard quality! Slow roast (too slow) stays unfortunately, a urban legend! Talking about the roast, we wanted to do a knowledge game… Do you know which are the organoleptic proprieties we develop in coffee on each roasting phase? We have made this graphic (very illustrative) about the coffee development during the roast… can you help us to explain or identify what each phase designed in our curve? What does each image mean?

Courbe de torrefaction EN

Until the next, Belco’s lab team !
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