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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