As I mentioned previously there appears to be a “donut” shaped sweet spot in the roast. I had been testing my SR500 with a K type thermocouple in various spots. Most of the time people run their roasters with the thermocouple shoved straight down the middle in a lot of the photos I’ve seen. With the SR500 I’ve found this region to be very sparse with beans due to the high flow of air up the middle.
As shown in this diagram the center portion at the bottom shoots up the middle in the air column grabbing beans on the edges of the two green zones. They are then tossed outward in the orange circular zone represented on top. The beans that sit out on the purple areas on the bottom tend to burn due to low circulation. Ultimately I would expect some sort of triangular slanted chute sealed to the edge would allow beans to be directed away from this burn zone and closer to an area where movement would be possible will help improve this.
I have not written much lately because I’m currently not at home using my roaster. Prior to leaving I did some testing of the sweet spot ultimately getting pretty close to the middle of that sweet spot. No matter which beans I roasted and the length the beans were being roasted I always noticed, while adjusting fan and temperature settings on the controls, that the beans always had first crack at the expected temperature +/- 1 degree Fahrenheit. The same with second crack seemed to hold true as well.
Based on those readings and the reproducibility of that it is my opinion that the ideal thermocouple position in the SR500 and probably the SR300 is as I described earlier. The height seems to be just below the surface of where 120 grams of beans fills the roasting chamber to for the tip. This keeps it from the bottom where the heat is somewhat higher and allows it to be centered in contact with the main mass of beans once they expand slightly and begin to float more easily in the air column above his position.
Regarding the coffee’s I’ve roasted. I previously mentioned some by name and certain characteristics of the roast as I was roasting them. I had decided until I can track the actual temperatures and accurate times to share it was probably best not to continue posting the resulting curves as I roasted them.