Coffee Data Science
Post-Roast Coffee Cooling Experiments
Post-roast processing
In my experiments on the Roest, the post roast cooling and processing has been of great interest. The Roest has a fan to pull air through the beans as they cool, and I wanted to see how doing a few other things might affect the beans in terms of taste and extraction.
I did a few variations across two coffee bean types:
Colombia:
- Baseline
- Vacuum: throw the beans into a vacuum chamber immediately after drop with the vacuum pump running
- No Vacuum: throw the beans into a vacuum chamber immediately after drop without turning it on
- Freeze: throw the beans into the freezer onto a metal tray immediately after drop
- Heat Soak: After beans cool, heat soak at 50C for 10 minutes
Honduras:
- Baseline
- Freeze: put beans into Vacuum chamber sitting in ice bath without turning it on
- Vacuum Freeze: put beans into Vacuum chamber sitting in ice bath with the vacuum pump running
Freeze for this test:
Vacuum Freeze:
Post Roast Metrics
These tests had some roast variations, so I had to deal with some noise. However, the weight lose was mostly similar.
Moisture also stayed mostly the same. These were measurements after the beans had reached room temperature.
Water activity was pretty consistent, but I’m unsure the value still.
The beans had similar densities, but there were variations.
Coffee color is probably the most important, and all of the roasts were close in coffee color. I consider within +/- 3 points of the average across experiments for whole bean color to be a good indicator that they achieved a similar roast level.
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).
Shots
Starting with the 5 Colombian variants, I didn’t see an improvement. I really didn’t see much change that could be a pattern.
EY for all of these shots was also similar.
For the Honduras variants, Vacuum Freezing seemed to pull ahead.
Reorganizing the data shows that vacuum freezing does seem to pull ahead. This is quite challenging of a process to do at home, but maybe a freeze dryer could do this efficiently.
EY for all of these shots was also pretty consistent.
I theorized these cooling methods would produce something valuable, and one did (freeze vacuum). Maybe the valuable insight is that cooling the beans quickly does not matter as much as I had thought. Maybe only bringing the beans below caramelization levels is key. I don’t have a good measurement for bean temperature post-drop.
More experimentation should be done on freeze vacuum processing post roast. I wonder if there would also be a benefit to heat soaking the beans afterwards.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
