To further my thinking of how the fan mitigates energy during the roast. We also need to think of the way we are cooking the beans and how that is different (then a drum). Because we are not using a lot of conductive energy, the transference of said energy to the center of the bean is largely buffered. What is being buffered? warning: personal beliefs ahead The embryo of the coffee seed (bean), the embryo is where most of the ingredients for creating the flavor are being held. The surrounding cellular matrix composed of cellulose, minerals(etc.) and the result of the processing method contribute to the second portion of flavor that you can get out of the bean. The fastest way to get to the center of a Tootsie Pop is to lick faster, and so by increasing the contact time and speed (friction) of your tongue. And the fan is licking the beans, removing water instead of sugar as in the case of the lollipop. But that is not to say enough heat from the coils can’t be applied in the beginning to get to the bean faster. As well as fast enough fan will wipe away moisture and start cooking the inside faster. So it’s a balancing act of which kind of the 2 energies should be applied. In what ratio will determine the outcome. As an example think of the Anduino profile and it’s high charge to a temp. By applying enough energy via heating coils there can be such a significant increase in temperature that the beans will reach 1C very fast, but is slowed down by the fan speed. Like wise the “S” Curved profiles can use a steady fan because the heat applied is very gentle.
I wouldn’t think of it as cooling, or you could. But maybe more like evaporative slowing. I think the answer for why the beans get darker is a matter of pressure. With a high fans speed there is a negative pressure occurring in the chamber and as the fan slows the pressure of the chamber is increasing and the focal point of pressure aka the point receiving the most energy is the center. Which could explain why when I cut the beans of a profile with a decreasing fan starting around 1C the center is darker and the beans taste “baked out”.
It does seem to add more energy, the beans do cook a little more but I think mostly it is because the metal grate where the fan is, is so hot, as well as the walls are very hot. The conductive energy of the metal at that temperature does have a significant effect. As well as that energy differential between bean to bean that from ones that held more heat and those that held less are able to “even out” so to say. That is at least, what I think is going and I’m not sure it is correct or not.
Because like was also mentioned in the Ikawa SCA video, the fan is tied to the heat and so with an increase in fan, there is an increase of energy given the same amount of heat input from the coils. It would be best to think of these phenomena as which heats the beans more than the other and in what combination. Only because having an actual cooling effect will have negative effects on the roast outcome and so any dip that the physical bean temp takes will have a negative taste effect (I can be wrong, but for this I doubt it).
Lastly towards the end of the roast (and also something I’m going to start another thread to discuss, is that for us air roasters, the main contributor to color is set by the temperature momentum on the profile) there is very little we can do to ultimately change the color (at the end). But also through observation (and maybe I’m remembering wrong) an increase air speed (at the end) will cook the outside more than the inside, but the bean is very resistant at this point. But what is weird is that the oven thermometer I set up to measure the environmental temperature will increase faster no matter when, if the fan speed is faster.