I was at a friend's house checking out his new ECM. He's an acoustics guy (think submarines) and sent me this paper from 2014.

Coffee roasting acoustics
Preston S. Wilson

J Acoust Soc Am 135, EL265-EL269 (2014)
https://doi.org/10.1121/1.4874355

Cracking sounds emitted by coffee beans during the roasting process were recorded and analyzed to investigate the potential of using the sounds as the basis for an automated roast monitoring technique. Three parameters were found that could be exploited. Near the end of the roasting process, sounds known as "first crack" exhibit a higher acoustic amplitude than sounds emitted later, known as "second crack." First crack emits more low frequency energy than second crack. Finally, the rate of cracks appearing in the second crack chorus is higher than the rate in the first crack chorus.

- https://pubs.aip.org/asa/jasa/article/1 ... -acoustics

This is essentially how the roast detection in the Roest works - you can adjust the sensitivity and number of cracks to ignore before recording; it then displays the transients on the roast log.

I love it when someone does a study that determines what we already know...

Part of the reason that I posted this almost-decade-old paper was that we are starting to see the implementations. I believe Probat introduced automated detection in their huge industrial roasters a few years ago, and now we are seeing detection in relatively-affordable roasters like the Roest as mentioned above, and also the recently-introduced IKAWA Pro 100x.

Anything that can help make roasting less variable is something good. All too often I have ordered a bag of some micro-lot and liked it, immediately ordered more bags, and recieved the same coffee, but not roasted in quite the same way. That's one of the main reasons I dove deep into home roasting.

This guy stuck a microphone in his gene cafe.
https://homeroasters.org/forum/viewthre ... ost_77107

Has me wondering about adding a microphone, and see if you could use some software to detect first crack?

I recently missed first crack on a roast, and because I didn't believe my other senses, went too dark in the roast.

Randy

"There's an app for that"

Sorta. There are several (free!) audio spectrum analyzer phone apps posted over the years since that paper was published. Not optimal for honing in on crack sounds, but an enterprising coder could adapt one specifically to coffee roasting - could get ten's and ten's of downloads

Isn't a crack sound the lowest possible sample size for determining the overall roast progression? If I repeat the exact same profile with the exact same green and batch size, I can still hear first crack sounds land within a +/-10-second window, 'cause I presume no two beans are alike, and the bean that cracked might have been stepped on, splatted with bird poop, whatever.

Batch to batch variation can be a good thing sometimes, as it could expose a weakness, a potential improvement - or get one to do it themselves, which is even better.

randytsuch wrote:Has me wondering about adding a microphone, and see if you could use some software to detect first crack?

For about the same amount of labor and cost, you can install a roast gas detector. The gas detector can even provide a full minute advance notice for an impending audible first crack. Humidity sensor on exhaust - other gas sensors ?

I have a diy'ed SCTO roaster, so that's not going to help me. Your exhaust sensor does look interesting. I use an ESP32 to read TCs and to control power via PWM on my SCTO. Unfortunately I don't have an exhaust to cool down and monitor.

I was really kind of thinking out loud, honestly probably small chance I'll follow through with it.

I played around with an accelerometer and found I could detect first crack, never took it to second crack but I stopped using it as detecting it by ear is pretty simple once you agree with yourself how many pops in a row represent FC.