Coffee Data Science
Refined Charge Temperatures for Coffee Roasting Feasibility
Charging forward!
Previously, I explored charge for roasting, which is the temperature the inlet air is at when the green beans drop into the roasting chamber. I had looked at 100 C, 191 C (baseline), and 300 C. 100 C was worse than 191 C, and 300 C was the same. So I squeezed my range of charge temperatures to test:
- 150 C
- 191 C (baseline)
- 250 C
Post-Roast Metrics
The metrics didn’t have much trend, but maybe density needs a double check.
Coffee color was close enough given that the roasts were all ended by final bean temperature at 212 C.
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).
Shot Data
From four feasibility shots, the data might suggest that 150 C is similar to the baseline while 250 C outperforms for each shot pair.
There weren’t noticeable affects on EY.
This test suggests I refine my search space between 191 C and 250 C, so I’m doing another feasibility test with 225 C. If this test shows improvement, then I will expand to a few other coffees to see how higher charge improves taste.
This is particularly interesting because I had issues roasting an Yemen bean. Hiver at Chromatic Coffee suggested going to a much higher charge.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso