Coffee Data Science
Extended Dry Time for Coffee Roasting
Why did that one roast taste so bad?
As part of a casual “why not throw coffee beans into a sourdough loaf”, I found the worst tasting coffee of my life. It was astonishing in some ways because I never thought to remember the worst, only the best. I want to better understand what made it so bad so I could potentially find some improvements.
The original roasted beans baked in a sourdough loaf for 1 hour, and the highest temperature they reached was 100 C internally. Then I roasted the beans with a regular roast after pulling them out of the loaf.
I thought maybe the long dry time could have caused the problem, so I did a roast at 100 C for 18 minutes. Then I re-roasted it.
Post-Roast Metrics
The metrics were similar across the board.
However, the final color was slightly off even though the final bean temperature was the same (212 C) for both.
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 pairs of shots, and the baseline was better as expected. The 100 C dried was not super terrible; it just didn’t taste as good. There were no categories that stuck out or became unbalanced.
EY was about the same across the board, so this process didn’t affect extraction potential.
Now I wonder if I had dried it at 100 C for 1 hour, would the results be far worse or just slightly worse. This is no where near as bad as my sourdough loaf roast, so I need another test. The way I baked the beans at 100 C also allowed moisture to evaporate, and I suspect the beans being inside the sourdough bread did not allow moisture to evaporate. This will need to go into the next design of experiment.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
