Roasting this Nicaraguan Geisha and it’s FC comes soooooo early. I know it’s not misreadings by the Bullet because the IBTS and BT Probe track really nicely and there’s no significant variation to cause concerns. FC was ROLLING around 195C but started around 192/193C. I’ve never had a bean hit FC this early before. Just curious to see if anyone else has? Beautiful roast curve too 
Yep, that does seem early! I have no experience with that bean.
One thing Aillio mentions in their docs is that FC “drifts lower” as the IBTS sensor gets dirty. I suppose a stray piece of chaff could be stuck on it too?
But if you don’t see this kind of drift with other coffees (that is, your current FC temps are otherwise normal) then I would think it’s the bean.
Curious to hear what others say.
I wanted to say it’s probably normal for highly processed Geshas, but then I saw that yours is washed. So I checked your other roasts, and between all the beans cracking around 195-196, adding that the crossover between BT and IBTS happens far too soon, my money is on a dirty IBTS.
Good shout. I’ll clean it this morning and see how that affects roast logging
Forgot to say that you’ll need to adapt a great deal. It did seem odd that your PH is just at 270°C for a 775g batch. Preheating to that temperature, you should be around 187°C on BT at the start of the roast, but you’re starting at 205°C. That would be more of a 285-290°C PH. So, keep in mind that you’ll need to up the PH and adjust your roasting routine once the sensor is clean. Why do it then? Well, because it’s never a good thing when something as hot as that goes 10-15°C over set temperature without you knowing it. On max PH, which I think is 310°C, the machine would probably give an error and go into cooling mode, because you’d overshoot the set temperature.
I’m out town for the week but did clean the IBTS and other things before I left so we’ll see what happens when I get back an roast up some beans. I don’t think there will be a great deal to adapt to as most of theses recipes were developed a long time ago when temps were reading more accurately. Sure, I made minor changes here and there since the last cleaning I may need to adjust but I’m not expecting any significant challenges but I guess we’ll see what happens when I return.
@braca19452f9m you are right that the IBTS was dirty and giving higher readings that it should have. First two roasts since coming back and the initial BT reading was 184*
I’ll edit this once I finish my roasts for the day to see how the cleaning affected the recipes
Well, it looks good. The crossover is gone. However, the only 2 explanations I could think of about the BT readings is that you either have a different, older firmware installed, or you have a 110V machine that is somehow different, but the first one seems more plausible.
Sorry, I’ve misread the temperature. Disregard what I said. Everything is fine.