Coffee Data Science
Higher Drum RPM for Improved Tasting Coffee
Expanding on a feasibility study
After an initial feasibility study showed a higher drum RPM could improve taste, I expanded on the dataset with a few more roasts. I wanted to better see how this variable generalized, and I found 65 RPM (the maximum for the Roest) outperformed 55 RPM.
The key for this dataset is color consistency. I have much improved consistent roast development by dropping at the same end bean temperature. I was able to have consistence color except for one roast which came out much lighter (higher Agtron number) as seen below.
Then I looked at some espresso shot data.
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).
Shots
I pulled 23 shot pairs over 6 roast pairs. Taste certainly had a trend where 65 RPM tasted better.
I split this out by bean type to double check that there weren’t some outliers. A few beans had some borderline scores, but none were exclusively better at 55 RPM.
In terms of individual components, the biggest improvement was on the Sour and Bitter components.
From a TDS/EY standpoint, the metrics were very similar.
All the taste scores except Rich had a statistically significant improvement with a p-value < 0.05 for a two tailed paired t-test.
These tests have allowed me to increase my drum RPM to 65. I will revisit this variable in a few months as other variables are also fluctuating, so I can only claim a higher drum RPM is better for this roast level and this roast profile.
If you like, follow me on Twitter, YouTube, and Instagram where I post videos of espresso shots on different machines and espresso related stuff. You can also find me on LinkedIn. You can also follow me on Medium and Subscribe.
Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
