Coffee Data Science
Heat Soak in Roaster Post-Roast
Efficiency in Process for Heat Soaking
Heat soaking has a taste benefit to coffee roasts, but adding another process post-roast is annoying to me. I wanted to know how I could make this more efficient by leaving the beans in the roaster but turning off the heater.
Previously, I used a test roast to show that I could quickly drop the bean temperature while the coffee beans were still in the roaster, so I figured I could try this for a tasting coffee with the aim of 2, 4, and 6 minutes of heat soaking.
Post-Roast Metrics
I was able to get the roasts close but not as close as I would have liked. Part of this was due to the roaster still running, so the roasts left in would have more weight loss. However, there was a constant offset rather than a trend.
I thought it was weird that the 6 minute heat soak would have a higher moisture level.
In terms of roast color, all the roasts were within +/- 3 of the average, so that’s a good sign for a good experiment.
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 pulled four shot pairs for these roasts, and this is a small feasibility data set aimed to give some intuition at performance.
These shots didn’t show a degradation or improvement in taste.
I resorted these shots by the roast, and I see the same pattern with the except that the 4 minute heat soak (performs slightly worse).
EY didn’t show much difference.
While these tests showed the roasts held in the roaster don’t suffer negatively, they aren’t gaining the benefits of heat soaking. I wonder if a coffee coming back all the way down to room temperature and then back up to 50 C is the key to heat soaking. The bean temperature didn’t come down below 100 C, and other tests showed heat soaking above 50C made the coffee taste worse.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso