Less than desirable roast profiles. Under developed flavors

Hello Community!

This is my first post here so I appreciate your interest and patience. I have looked at other posts about this and read through them and after trying some of the advice from those I am still getting flat and grassy roasts. I previously roasted on a Diedrich IR25 and since leaving that and starting my own company I have been using the Bullet V2. Getting used to the controls and electronics is definitely part of it but have been roasting on it for over 9 months now. In the 9 months I have roasted around 250lbs of coffee.

My typical batch size is 2lbs, which maybe I am pushing that to close to the limit? I originally started preheating to around 400F but have since increased it to 437F but have not noticed much difference in an end result. My graphs were much uglier in the beginning but have gotten them to be more pleasant over the last couple of months.

Any thoughts or additional tips?

Here is a roast I did 2 days ago that came out under developed for reference.

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Well, for 32oz, I’d start with max preheat or maybe a little less, depending on the bean. Anyway, somewhere between 554 and 590. Also, it seems impossible to me that you have yellowing at 267 and cracking at 313. FC should occur somewhere between 390 and 410, and yellowing somewhere around 320-340 mark., depending on the bean. I can say with certainty that what you’re hearing isn’t the first crack. The Bullet is perfectly capable of doing 32oz batches and you’re not pushing it. Just up the heat and it will be OK after some practice. Happy roasting.

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Braca, thanks for the input on the preheat. I will give that a try. I did try increasing the preheat temp to 455F but then it felt like the roast went way too quick. It finished up in just over 8 minutes at an end temp of 420F. Like you said it is hard to believe that at those low temps those changes would already be happening. Looking closer at it the 313F is the IBTS temp, and my bean temp is showing 391F at that point. Second screenshot here for that.

Oh, in that case you should clean your IBTS if you haven’t already. It seems quite a lot as a difference. In any case, I don’t see how a 32oz batch can go so fast without a proper preheat. Something must be at fault, other than a dirty sensor, which most certainly is dirty. Might even be something with the scales or tare or something like that. I mean, it could be extremely old beans from more than 10 years ago, but I don’t see that being the case. Or maybe your bean probe is faulty. Looking closer at your profiles, the bean probe is signaling a preheat upwards of 500, and your set preheat was 437. Looking at your older roasts, it was signaling normally. Which firmware are you on? Other than cleaning the IBTS, you might want to try updating the firmware. The PH temperature target is measured by IBTS, so it being dirty, goes on preheating until it reaches what it thinks is 437, which is upwards of 500, as I mentioned. If none of this works, open a ticket with support.

P. S. Sorry if it was hard to follow my train of thought as I was typing while encountering new info. The last part, about IBTS and firmware, is the most important one because that’s when I had the full picture. Feel free to disregard the rest,

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I have to agree with @braca19452f9m … those YP & 1Cs points are impossibly low. And the difference between I-Temp and B-Temp is way beyond anything I’ve seen. If there isn’t something blocking the view port for the IR sensor then there may be a calibration error in IBTS. I’d suggest starting with cleaning the IBTS. If the roaster is new then maybe a call to the vendor is in order.


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Thank you both. I am very excited to check that out. I hope that is the problem as it should be an easy fix. It might be a couple days before I am back in my roastery but will provide an update for sure.

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I concur with what Bruce and braca said. Definitely go even higher than your planned 455F for PH if you’re roasting 2lbs / 1kg. You need enough heat momentum for the bean mass. I roast 1kg often and I preheat at 572F. My YP is around 330-335F at just under 5 mins, my FC is between 390-405F at around 8 - 9 mins. I drop between 425 and 435F depending on how dark I want it. These are ranges because it depends on the bean and various conditions. Feel free to search my profiles in roast.world they are all public. Yes at first when I transitioned to roasting 1kg from 350g and 500g it was a learning curve, but I found I get significantly more consistent “behavior” with 1kg. Caveat, I’m not saying my 1kg profile is “perfect” - what’s in the cup is key and that you like it. Also do a forum search as well, as there are several threads already discussing 1kg batches and transition from smaller batches to 1kg.

Happy roasting

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I took apart the roaster and gave it a good cleaning over the weekend and got some better results but it still seems a little flat/under developed to me. The temperatures seem to be more aligned since cleaning the iBTS as well so that is a big help. I am going to try and roast a little longer like you mentioned Lisa to at least 425F and see it that helps give me a better flavor profile. Here is one of my roasts post cleaning this weekend.

@delpostocoffee.lg8G I would like to suggest to use the BT temp readings once you reach FC. I can see there you are already at 422 in this one that you provided screen shot of. The reason for switching to BT is that with 1kg batches it is more accurate due to bean mass than the IBTS - that’s been my experience. If you tried to hit 425 with IBTS you might end up with burnt beans. I also suggest to not change to F4 so soon, you’re drawing quite a bit of heat out with F4 which might be why the cup is a bit flat. Try stepping to F3 and let it stay there for a while. I usually don’t drop to F4 until after FC. This is one of my “last” roasts before I fractured my foot. Not saying it’s the only way, but just a reference for you (some will say that I have a “flick and crash” in that profile but I hadn’t found it affecting the cup according to my taste bud). There are others who roast using Munchow’s (sp?) method which is less “complicated” :slight_smile: but involves starting at high PH as well.

Happy Roasting


Interested in this thread. I struggle with the same issue.