Coffee Data Science
Drum RPM for Coffee Roasting
Rolling in some data
As part of my efforts to put a little bit of data on different roasting parameters, I did a short test on the drum RPM to see how that would affect the roast. Slower drum speed means a slower roast.
Roasting
I used Scott Rao’s roast profile on the Roest that uses bean temperature as turning points for inlet temperature. This is my baseline profile.
Roast Data
The bean temperature was easily affected, which should affect other bits of the development.
The Rate of Rise was most affected by the lower RPM, which also didn’t drop below 0.
The RPM affected the first crack time because the roasts took longer, but the number of cracks remained roughly the same.
Roast Statistics
I looked at a few post roast metrics to understand how these parameters were affected. The number of samples are small, so this is only to gain a starting point for intuition before other experiments.
The weight loss was similar and consistent with what I would expect.
The moisture change between the roasts didn’t make sense because there is no linear trend, so I suspect there is another variable at play.
Density has a slight trend.
Roast color has a different trend. So while the 20 RPM took longer, the roast was darker, slightly.
Tasting Equipment/Technique
Espresso Machine: Decent Espresso Machine, Thermal Pre-infusion
Coffee: Home Roasted Coffee, medium (First Crack + 1 Minute)
Pre-infusion: Long, ~25 seconds, 30 second ramp bloom, 0.5 ml/s flow during infusion
Filter Basket: 20 Wafo Spirit
Other Equipment: Acaia Pyxis Scale, DiFluid R2 TDS Meter
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 collected taste and TDS/EY data on three shots per roast. Again, this data is supposed to give some intuition; it is not conclusive. 55 RPM is what my other profiles use. 65 RPM seemed about the same in taste, but 20 RPM didn’t taste as good. It wasn’t as sharp or sweet.
For EY, all the roasts performed similarly.
These initial experiments are interesting to me as I start to get a feel for how input variables will change the output variables. Eventually, I plan to cross a few variables and then figure out an experiment with more coffees for a good data set.
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
