I’ve found the active noise cancellation on my Apple AirPods Pro works pretty well for isolating cracks from the rest of the noise floor. Worth a try if you happen to have them or something similar.
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So you just wear it and you listen closely from the drum?
This is an amazing idea! I was just speaking to my sister today about 5 roasts i did yesterday, and always have trouble pinpointing when FC starts. I’m going to try this on my next roast!
Hi Gilbert,
Yes, just listen through the stethescope and you’ll hear all the faintest pops throughout the roast. Let me know if you try it!
Squeakie, yes it’s a huge upgrade that takes a lot of the guesswork out of roasting (the timing of the FC and SC). Please post your feedback once you try it out.
Carldebar, Thank ou for this clear post, I am a hobby roaster in Amsterdam and orderded the sthetoscope and plugs on Amazon. My expierence is that with some beans and some roastprofiles, FC is really hard to hear, sometimes I hear nothing, and it must have heppend. Because I determine when to drop on delta time en delta temperature after FC calling FC is really important to me and I want to get more consistency in when to call FC. I do not think it matters when I call FC as long as do it consitently with all roasts. Thank you so much for suggesting an relatively easy solution. I can’t wait to try!
Thank you for reaching out and letting me know—I really appreciate it.
I think you’ll be amazed at how clearly you can hear what’s going on inside the drum with the stethoscope. It really takes the guesswork out of it.
Lately I’ve been roasting some Brazilian beans where FC is very subtle—more soft, sporadic pops rather than a robust, rolling crack. Even so, it’s still easy to identify when the crack begins. I’ve had excellent results with that added clarity.
Let me know how it works for you—I’d be interested to hear your experience.
This is great news. I came to the Bullet from a Hottop where the sounds of cracks were very easy to hear. The Bullet has a lot more bean splashing noise than the Hottop, probably because of the larger drum, so I just guess at FC based on IBTS readings. Not very accurate, but certainly repeatable. Hearing the cracks just might enable me to accurately calculate Maillard and development times instead of always wondering. Thank you for this information.
Taking the guesswork out of FC really is key if you want to be more precise with Maillard and development time. Once you can hear it clearly, everything downstream starts to make more sense and becomes more consistent.
One thing I’ve been experimenting with lately is using AI to analyze my roasts. I let AI do the deep research on each bean, then upload the finished roast graph and have it generate analysis and tasting notes. It’s been surprisingly accurate—especially how it ties the bean characteristics and the roast data together.
It’s also just been a lot of fun to play with. If you haven’t tried it yet, it’s worth exploring.
Are you using a particular AI program? Being able to directly send roast data and have it analyzed sounds like a great idea. I’m not aware of a program that allows you to do that.
@nomad Thanks for asking.
Here’s a link to a post I made about how I’m using AI:
https://community.roast.world/t/using-ai-for-bean-selection-and-roast-graph-analysis/20763
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Hey I like that high temp silicone stopper idea. I’ve been using a similar setup with a brass pipe fitting ever since I saw it on here way back when. Wondering if you still use the bean tryer with this setup? Can you put the stopper in and out easily?
Pretty much impossible for me to hear soft cracking beans without this.
@billyjackskin.Tdzn I don’t use the trier at all. At this point I rely entirely on my roast recipes, which have gone through multiple iterations and tweaks, with some AI assistance along the way, so the trier just isn’t necessary in my case.
Another reason I avoid using it is that every time the drum is opened to outside air, it affects the roast. The cooler ambient air rushing into the drum will pull temperature down, and you can see that immediately in the roast curve.
But yes, the stopper is fairly easy to remove. The only caution is that if you pull it during a roast, the surrounding metal will be very hot, so you need to be careful.
I don’t use it either. It’s really too small I think. Was just curious. I always see the Aillio guys using it though. I don’t run too many recipes because it seems like I always have a new bean going. A lot of peeps here will say you don’t need to hear FC as you can tell by the IBTS when it’s occurring which is true but I always like to listen and mark it when I have a good consistent cracking starting. I kind of doubt we’ll ever see the Aillio guys with a stethoscope but I can’t go without it now. 
@billyjackskin.Tdzn Same here. I roast a lot of different beans too — right now I’ve got more than a dozen greens on hand from all over the world, and most of what I roast goes out the door to friends.
My experience has been that you really can’t depend on IBTS alone as a marker for first crack. Even with the same bean, it can shift depending on ambient temperature and humidity. I’m not looking to get into a debate about it, but that’s what I’ve seen from hard empirical data over a lot of roasts. For me, the stethoscope pretty much ends the debate. It lets you hear exactly what’s happening instead of inferring it indirectly.
What’s been interesting is that, with AI helping me remove so much of the guesswork, even on a new bean I’ve never roasted before, the first roast recipe now usually lands very close to where I want it.
If you haven’t seen it, check out my other post about using AI to help tweak recipes.
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I have had good success putting my ear right next to the hopper plug. As I near the suspected time of first crack, I slightly lift the hopper plug as if it were on a hinge…every 5 seconds and I only open it a tiny crack for a moment to make sure air doesn’t rush in. Any air that may rush in will be just part of my routine curve. Not sure if it is my imagination but also seem to feel the vibration of the cracks with my fingers on the silicone plug.
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@franzusa, I used to do the same thing, but I eventually got tired of lifting and closing the hopper plug over and over. That’s what led me to come up with the stethoscope mod, and it has improved my results quite a bit.
What I’ve found is that when a bean reaches the point where the remaining moisture turns to steam, it expands and causes the crack. But the first beans to reach that point do not always give a sharp, clean crack. Quite often, if the structure is weaker, they make more of a faint thump than a true crack.
Those are exactly the subtle sounds the stethoscope picks up well, and in my experience they are not possible to hear reliably by briefly lifting the hopper plug. So if your method is satisfactory for you, that’s great, but for me the stethoscope has been a real step up.
Dear carldebar,
I have fixed a sthetoscope like you suggested and I did my first 3 roast with it. It is amazing!! I had trouble with some beans (especially Brazilian) to determine FC. Now I can hear every crack, also when in the back of the drum. So for the first time I can clearly call FC when I want. (at roling crack, so not singular cracks anymore but at least 4 or 5 very close together) . I read a lot about this but finally I understand and can hear it consistantly, thanks to you and the stethoscope! I also roast many different beans but small quantities, so every roast has a different time and temp to FC. What I focus on is delta time and delta Temp after FC. I did a lot of experiiments with this and I seem to like de delta time about 1:15 to 1:20 and a pretty high delta Temp of 8 to 9 degrees (Celsius). I also do not use the trier and ROR is less important for me then delta time and delta Temp after FC. I calculated my own roast profiles not with AI but with regression techniques (LN an root functions) I think that is fun and I am a little weary of AI because I do not know the source of information an had a lot of nonsense with it (AI insists Ground bean color is always darker then Whole bean color???)
Thanks a lot this stetoscope will improve my roasts and my experiments with roasting!!
Oscar
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@oramspek.f7aJ
Oscar, thank you for the feedback. I’m very pleased to hear how much this has improved your confidence in calling FC. It has been a real game changer for me as well.
Your delta method makes a lot of sense. It is a reliable way to measure development because it focuses on what happens after FC rather than depending too much on absolute time or temperature, which can vary quite a bit from bean to bean.
What I’m actually doing now is something of a hybrid between DTR and delta. I use DTR as the primary target, but that target is different depending on the bean. Then I look at post-FC delta time and delta temp as a secondary check to confirm that the roast finished the way I intended. So in that sense, I’m not relying on a one-size-fits-all DTR, but on a bean-specific DTR with delta helping validate the result.
I also agree completely that being able to hear FC clearly changes everything. Once you can hear it consistently, a lot of the guesswork disappears.
@oramspek.f7aJ
Here’s an example of the kind of feedback I get from Grok when analyzing a roast.
This is an excerpt from a first-time roast yesterday of Burundi Dry Process Kibingo in high ambient temp:
“Bean-specific DTR (20–25%) remains the primary endpoint target. Here the actual 25.4% is only 0.4% above the upper tolerance, which is well within acceptable variance for a first roast of a new lot. The secondary corroboration metrics — development time of 3:08 versus a 2:30–3:00 target, and delta temp of +47.8°F — are in strong agreement with the DTR. The slightly extended development window and corresponding temperature rise reflect predictable hot-weather phase compression rather than any momentum problem, bake, or under-development. No conflict exists between DTR, delta time, and delta temp; all three confirm a properly shaped, gentle finish that maximized caramelization and body without scorching or rushing the endothermic dip.”
That kind of analysis has been very useful for me. I use bean-specific DTR as the primary target, then delta time and delta temp as a secondary check. It helps confirm whether the roast really finished the way it was intended to. Check out my post at Using AI for Bean Selection and Roast Graph Analysis
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