Coffee Data Science
High/Low Fan Start for Drying in Coffee Roasting
Tweaking the start of the roast
In recent experiments, I started tweaking the start of the roast during the drying phase, and in this experiment, I looked at exhaust fan speed. I already tweaked the fan speed during the Maillard reaction. For this feasibility test, I looked at three variants for bean temperature less than 145 C:
- 100% Fan Start
- 75% Fan Start (Baseline)
- 30% Fan Start
I theorize the 30% Fan Start will taste better because slowing down the fan speed was better for the Maillard reaction. I also expected the higher fan speed to produce worse tasting coffee.
Based on the Bean Temperature over time, the 30% Fan Start roast was a bit slower.
Post-Roast Metrics
All of these roasts ended up with similar metrics, which is good because that means any differences in taste are caused by the roast rather than the development time.
The coffee color is the best indicator that the roasts were close in development. All these roasts were ended at 212 C bean temperature.
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
On the first look, it seems 30% Fan Start is better than the baseline.
The 100% Fan Start was slightly lower than the baseline, but over the last two shots, it was okay. These shots were taken over a few days.
The EY wasn’t too different across the roasts.
This feasibility test showed reducing to a low fan speed during the drying phase improved taste. I will continue down this path to explore if this result was specific to these beans or if it better generalizes.
These experiment continue to be more complex and interesting as I vary different parameters.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
