Coffee Data Science
Heat Soaking Coffee Post-Roast
A larger dataset
Previously, I looked at heat soaking a coffee post-roast to see if it improved flavor. Heat soaking is often used in industry for a variety of reasons, so why not coffee? I found some initial improvement, so I collected more data across a larger variety of coffee beans to examine statistical significance.
After the roast, I put the beans in a 50C instant pot (set on sous-vide) for 10 minutes.
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
I ended up with 24 shot pairs across 5 roasts. I saw a big improvement across the board aside from 1 shot pair.
There was not a dependency on the bean origin.
All the score metrics were bumped up by 2 points, which is big.
In terms of extraction performance, both the baseline and the heat soaked beans had similar extraction. I suspect whatever mechanism improves flavor is not tied to extraction efficiency.
In terms of statistical significance, I used a two tailed paired t-test, which found all the taste scores were statistically significant, but the extraction scores were not.
These tests show great promise for heat soaking, and I’m more curious to understand the mechanism at play.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
