Café Naturêve Blog

Almost every educational article will tell you that there are three types of heat sources in coffee roasting: convection, conduction, and radiation. But in those articles, how to effectively utilize these three types of heat is rarely discussed.

Table of Contents

1. Convection in Aillio Bullet R1/R2
2. Easier Way to Understand Convection and Conduction
3. Differences in Flavor
4. How to Modulate Convection and Conduction

Yes, coffee beans are very sensitive ingredients. The entire roasting process, as well as the brewing stage and even after brewing, are all affected by temperature — this is true. This is why we need to understand the effects brought by different heating methods.

Convection in Aillio Bullet R1/R2

Although the Bullet roaster is often criticized for not producing sufficient convection heat, I actually see that as an advantage. With fewer factors to consider, roasting becomes relatively easier. Of course, different ambient temperatures imply different convection, but if the air is further heated, things become even more complex. That’s why we say the Aillio is a very user-friendly roaster—because you only have to control three things: power, fan (airflow), and drum speed.

Easier Way to Understand Convection and Conduction

For beginners, it might be hard to imagine the difference between convection and conduction heat. Here’s a common example from daily life: after washing your hands, you want to dry them. To use a towel v.s. to use a hand dryer. Which one dries your hands faster?

Of course, it’s the hand dryer — because the air invades every nook and cranny between the fingers and the palms. The nooks between your fingers are just like the pores or uneven surfaces in a coffee beans. With more convection heat, coffee beans naturally heat up faster.

Either way, you can understand the difference academically: Conduction heat affects your beans only when a part of the bean is in contact with the drum or its surrounding beans, while convection heat affects the beans constantly as long as the drum is not a vacuum. Therefore, if possible, rely on convection heat as much as you can not only because it’s more efficient, but also the flavor profile is cleaner.

Differences in Flavor

A roaster that relies mainly on convection heat can produce a cleaner flavor profile, according to the feedback from the market. Why is that? I believe that many moisture contents and terroirs are adhered in the nooks of a coffee bean. Using hot air (convection) to blow is a more thorough way to remove terroir. Be careful not to blow too much, otherwise coffee beans lose too many flavors and terroirs.

As for radiation heat, I haven’t studied it in depth, but I imagine it becomes more noticeable after back-to-back roasts, when the machine’s whole body gets very hot.

How to Modulate Convection and Conduction

It’s all about “ratio”. Adjusting the ratio of convection and conduction according to the nature of a bean and the weather of the day is the key to roasting. This post will be shared with paying customers.

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