Common Roasting Problems - By Dave Corbey
There are a few defects/roasting problems that can sometimes be seen when examining the roasted bean. I will try and give my thoughts/guesses as to why this happens and how to perhaps reduce or eliminate them.
I don't know how else to describe the issue I'm having - they look like little holes, in the bean. I have a horrible camera and this is the best shot I can get. If you look at the bean on top, I think it's got the most visible holes. They don't go all the way through, just through a layer or so.
What are these, and why do they occur?
It's hard to see from the picture that was provided, but I don't believe he was talking about insect holes. To me it looks like "spalling", the black divots that look as if a circular or oval bit of the bean has been gouged out with a black patch shown in the picture.
His is a clearer picture of this problem with the faults highlighted.
If so, it's usually a sign of too much heat in the roaster. Generally this would be during the roast not necessarily at the drop. Tipping or scorching is often because of too high a drop temp in a drum roaster. The spalling usually results when it gets just too hot. Try roasting the same beans again, but at 1st crack try and reduce the heat input (not the temperature, if that makes any sense). Your objective would be to try to get the beans hot enough to have a decent 1st crack, but not to let them get too hot. A plateauing off of the temperature curve.
My guess would be that the beans are a soft bean of some kind, but with enough temperature abuse this happens on SHBs as well.
P.S. If the max temp is not too high and you're still getting them, see if you can reduce the rate of temperature rise in the roaster a little (if you have that element of control).