Given that we can’t conclusively prove anything without an actual lab, BUT that its also an interesting thought experiment, lets try to draw some conclusions
Let start with listing all the potential factors (and I invite any reader to add to this list).
‘Lower Agtron’ or ‘Darkening’ or ‘Browning’ factors:
All these browning factors are temperature related, more specifically they concern: q(something-bean) [The heat transference from ‘something’ (hot) to the (cooler) bean].
So which factors are there…:
q(air-bean) (this is the main function of the IKAWA)
q(chamber-bean) (depending on where the heat element is stored T(chamber) could actually be higher than T(air))
q(bean-bean) (given the other two q’s I assume this one negligible)
What also might play a role is the first crack, as the water then vaporizes from the bean (around ~200C). Think of higher humidity, less (or more?) internal heat conduction (k), …?
And then there is of course t(ime). Over time everything turns dark
So we have a physics process inducing chemical reactions. My background is in physics not chemistry, so I can’t much tell about the reactions. It could for example be that if you keep the temperature for a long time at 160 you get a ‘better’ maillard reaction leading to a darker roast. However given the fact that pyrolisis of organic material tend to have an end result in black, I think its a safe assumption that the last stage (Pyrolysis) has the biggest impact on the browning of the bean.
Hence I think there is some basis that the browning is mostly influenced by exposing beans to a T > 220 high enough temperature for a long enough period of time.
Given that the premise is to find an explanation for lowering the fan speed leads to a lower agtron number (more browning) we’re looking for a process that increases q (heat transfer) from ‘outside factor’ to the bean and possibly a process that keeps the beans at a high temperature.
Now the theories:
- as mentioned: its possible that a lower fan speed leads to more q(bean-chamber), which could explain the browning
- lowering the fan speed keeps vaporized water (after first crack) longer in the chamber, resulting in a higher humidity, resulting in a higher k (heat conduction)
- lowering the fan speed could delay the first crack (is it? this is actually something you can test!) allowing better k in the bean internally, meaning a ‘hotter’ core meaning that the bean keeps warm longer during the cooling fase.
- as mentioned: k(bean-bean) is higher at lower fan speed (because they are longer in contact).
I’m still voting for 1. Not that I’m really convinced that its 1. It’s just that I’m reasonably convinced that its not 2,3, and 4. I have some arguments as to why, but I’ve rambled long enough now…