After installation of the new IBTS sensor and the new power board in my originally V1 Bullet (at 240V), I am now able to compare the roasting results. Using the same coffee a Guatemala Antigua, and after a period of seeking and exploring, I now have the feeling that we have found the best control actions to get out our most preferred profile. We set out for a roasting duration of about 10:30 minutes seeking for a slowly decreasing ROR to get to an espresso roast which you might typify as nicely balanced, with sweetness in the cup, a slightly bitter touch together with a hunch of citrus. The beans are evenly colored with a slightly silky shine.
We start with a temperature of 230C (IBTS) and power at P8. Our ROR climbs directly to a level around or slightly over 20. In the bread phase, around 170C, power goes down to P7. At the start of FC Power to P6 and then slowly back to P5 and P4 depending on your observations. ROR wil ideally be between 8 and 3 in that period. After 10:30 roast will be ended at 219C. For filter roasts we stop at 215C.
It is very clear that the new power board is a bit more powerful, as we used to start at P9. I think that the IBTS sensor is a bit more realistic. FC and dumping temps correspond with my experiences with a bigger machine, a Probat 5 kg.
I look forward to the RoR based on IBTS as well as a levelling algorithm. But in the meantime, I feel the Bullet performs excellent. I will soon also compare the roasts with batches of around 900 grams.