Coffee Data Science

Extending Time per Phase of Coffee Roasting

Time Experiments

Previous experiments didn’t show a benefit to extending the length of the whole roast, but maybe individual phases of the roast would benefit. In this feasibility experiment, I looked at stretching each phase by 2 minutes using my Slope V2.2 positive pressure profile:

1. Baseline
2. Extended Dry
3. Extended Maillard
4. Extended Development

Example of Extended Maillard

Post-Roast Metrics

The metrics were interesting. Density was higher for a longer Maillard process.

Moisture was higher for an extended development. Color was close, but Extended Dev ended up being darker (lower Agtron number). This is more apparent from the ground color vs whole bean.

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

I pulled four shots for each roast, and the results did not give a clear direction. Extended Dry and Extended Maillard were not an improvement. Extended Dev gave a slight improvement in 2 of 4 cases.

Averaging the shots for all the score metrics, Extended Dev gives some signal for improving the Sour component. Extended Maillard showed through many components that it was worse.

EY was unaffected. One shot was an outlier at 20.0% EY.

If extending the phases doesn’t improve taste, maybe shortening them would. Further tests are planned to sort out this nuance.

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Further readings of mine:

My Second Book: Advanced Espresso

My First Book: Engineering Better Espresso

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