Coffee Data Science
Positive Pressure for Coffee Roasting Encore
More data but closer color
Positive pressure during coffee roasting occurs when the inlet fan is pushing air into the coffee faster than the exhaust fan is pulling air out of the coffee. I previously looked at positive pressure, and while I didn’t find a taste improvement, I did not find a degradation when the baseline coffee was 10 points higher on the Agtron color score (meaning that it was a lighter roast).
To explore further, I aimed to have a closer color for the beans at the end of the roast with positive pressure. I achieved this goal by ending at the same bean temperature, and I compared two roasts.
Post-Roast Metrics
I used a bean from Costa Rica and Burundi, and the beans roasted very differently. However, all the metrics measured post roast showed the roasts to be equivalent.
Most importantly, this is true for color, which was at most 2 points off.
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
This is a feasibility size of data, and I thought it might tell me a good direction to go. However, in the 8 pairs of shots (4 shots per roast), I did not see much.
Some of the shots were better or worse, but the response wasn’t a clear indication.
I plotted the data as a scatter plot, and there might be a slight preference to a higher internal fan speed.
EY did not sure much to be desired.
This data shots positive pressure might give a slight increase, but that is still a bit unclear. More data might be more revealing or show that this technic is not worth the hassle. I will pause this investigation for a bit until I better understand the other variables.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
