Coffee Data Science
Dropping Middle Thermal Pulses in Coffee Roasting
Exploring thermal pulsing
I have been exploring the properties of thermal pulsing to better understand how it works to see if I could optimize it. Previously, I tried dropping the first two or last two pulses, and I didn’t see too big of changes on taste, so now I will focus just on the middle two pulses to see how they contribute to the profile.
I roasted these on the Roest, and I made a few modifications for the profile by dropping one or both of the middle two pulses.
The result in Rate of Rise (RoR) follows a similar trend, but dropping both middle pulses slowed the roast down.
The same can be see in the bean temperature.
The first crack was similar except for the longer roast of Dropping the 2nd and 3rd one.
Post-Roast Metrics
The roasts had similar numbers except for the last roast (Drop 2nd and 3rd).
Roast moisture didn’t account for much.
Water activity was a bit higher for the last one. I’m still figuring out the use for that metric post-roast.
Density was lower for the last roast.
The lower density and the darker color suggest the last roast was darker. The baseline was much lighter than the last roast and had enough of a difference with the other two roasts to be concerned a little. I would prefer to have the roast color similar to have more control, but the differences point to the differences in the roasting process too.
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).
The Shots
I pulled four shots with each roast. All of the non-baseline roasts performed worse, particularly the slower roast in the Drop 2nd and 3rd. There was one anomaly in the third shot. .
We can re-orient these by the shots, where each roast had a shot pulled within 24 hours of the other. In this case, the baseline was higher on the 3rd shot.
There was a slight effect on EY particularly for the Drop 2nd and 3rd roast.
These roasts helped confirm that removing chunks of the pulsing doesn’t quite help, and this is good because it does not show a particular dependence on one of the pulses. While I was concerned about the darker color for the Drop 2nd and 3rd roast, I’m unsure how it affected the taste because the taste was very flat a muted, but it didn’t taste more bitter as I would expect from a darker color.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
