Hi DJR.

I think that keeping a shiny outer shell would be helpful. The one you need to watch would be the drum.

I have found an easy way to raise the emissivity. I was lucky that my drum was already internally dark by usage (oils). Following the same principle, I decided to lightly sand the outer wall with 300 sandpaper. Then I applied a thin coat of cheap vegetable oil. I put it back on the roaster, and I let it burn the oil at 550F ET. It took ~ 45 minutes before I could not see any white smoke come out any more.

This is a before and after:

Before



Note above: see how dark the internal wall is



Note above: see the new dark color developing.

I decided to take the drum out and now I am going to apply a second coat of vegetable oil and let the roaster run ~ 1 hour

Cheers

yeap. It makes a difference. I did a sample roast and the first crack came out like from a machine gun. The second crack was also very loud and fast. It never was like this.

This a 300 gram roast of Kona beans.



Note above: I also use a heat gun after Dry End till 1C, but I can tell you I never got high crack speeds till now.

This is how the outer wall of drum looked after the second coat of oil



Cheers

PS: At a stable ~ 550F ET, the heater elements don't emit any visible light. It is probably all mid-long wave infrared and convection.