Coffee Data Science
How much Heat can a Coffee Bean Hold?
Super long slow roasting
I wanted to explore how quickly coffee beans absorbed head and how long it took them to reach an equilibrium. To accomplish this, I made a roast profile where I manually increased the temperature by 5C every two minutes, and then I started increasing by 10C. I used the Roest, and I had to do this over three roasts because there is a maximum 20 minute time limit in software.
The results were interesting as the coffee beans never quite hit the target temperature. There came a point where the inlet temperature would stabilize, which is probably how the PID is designed.
I zoomed in a few times to see how quickly the inlet temperature was able to hit the target temperature. There was a drift as the temperatures went up.
There was a bit more fluctuations which is linked to the P (Proportional) parameter of a PID controller.
This gap increased to 40C by the end of the roast.
I looked at these segments at a few time markers, and I found 45 seconds after a target temperature change to be interesting. There was a drift in bean temperature that increased as inlet temperature increased.
I also looked at 75 seconds, and the trend was similar.
I don’t have a solid conclusion other than beans not holding temperature like we think they do. I’m curious to try this experiment again with high fan and drum speed to speed up the roast and the time it takes for the temperatures to settle. I may also need to increase to a 150g batch size to make sure the bean probe is covered.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
