Coffee Data Science
Heat Soak Temperature for Coffee Post-Roast
Soaking temperature explored
Heat soaking has become a helpful add-on to post processing coffee for me, and it has improved flavor. However, I don’t know how well optimized the process is in terms of temperature and time. So I explored temperature of a 10 minute heat soak to get some insight on a small amount of data.
I roasted one coffee in four batches on the Roest, mixed them afterwards, and split them again into four roasts to do heat soaking using an instant pot set on sous-vide (without water inside):
- Baseline: No heat soaking
- 50C heat soaking
- 75C heat soaking
- 93C heat soaking, I couldn’t go higher in my instant pot.
My aim is to find a temperature for heat soaking that is good as well as not good. My hope was that with three temperatures, I can get a better idea which direction to explore next, if any.
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 4 shots for each roast within a day of each other. The heat soaking seems wins over the baseline.
I resorted these by the roast. 50C is the best, 75C is close, and 93C does have a dip. 93C tasted slightly baked.
I didn’t see any impact on EY, but the last shot did have a much higher EY due to other variables.
These tests showed me that 50C is a good temperature to do heat soaking. I didn’t see an advantage to higher for fear that the beans could start cooking again.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
