Coffee Data Science
Modifying the Turning Point in Coffee Roasting
Lessons from frozen
One of the observations from roasting from frozen was a lower temperature before the turning point. This is the point where the bean temperature starts to increase after the initial drop. So to modify this turnpoint, I modified the temperature before the turn point. All the roasts have a 250 C charge, but I modified the target temperature after the beans drop:
- Baseline, 250 C inlet until turn
- High Before Turn: 300 C inlet until turn
- Low Before Turn: 200 C inlet until turn
This allowed a lowering of the turn temperature, and this is a nuanced approach to temperature after the green beans are dropped into the roaster relative to only looking at charge temperature.
Post-Roast Metrics
The roasts had pretty similar metrics; all roasts were dropped at 212 C bean temperature.
The bean color was all within 2 points, which is good.
Metrics of Performance
I used two sets of metrics for evaluating the differences between techniques: Final Score and Coffee Extraction.
Final score is the average of a scorecard of 7 metrics (Sharp, Rich, Syrup, Sweet, Sour, Bitter, and Aftertaste). These scores were subjective, of course, but they were calibrated to my tastes and helped me improve my shots. There is some variation in the scores. My aim was to be consistent for each metric, but some times the granularity was difficult.
Total Dissolved Solids (TDS) is measured using a refractometer, and this number combined with the output weight of the shot and the input weight of the coffee is used to determine the percentage of coffee extracted into the cup, called Extraction Yield (EY).
Shots
I pulled four shot pairs, and the results were interesting. A low turn point outperformed the baseline half the time, while the high turn point outperformed 3 out of 4 times.
EY was unaffected.
The data suggests exploring a higher turn point, but there is still some confusion with the charge temperature. Also, when roasting green coffee from frozen, a lower turn point occurred, and the taste was better, so more feasibility tests need to be done to better flesh out what is going on.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
