Coffee Data Science
Thermal Pulsing for Coffee Roasting
Bringing pulsing to the world of roasting
While trying to make some bad roasts, I made one called HotColdHot where I had a pulse go through the temperature profile. Surprisingly, it tasted pretty good. This got me curious about pulsing because pulsing is used in a variety of ways in engineering, and the technique can be applied to coffee.
A bloom during espresso or pour-over is quasi-pulse because it is a disruption in constant flow. I have also examined pressure pulsing in espresso, which gave some improvements in extraction.
To apply this concept to coffee roasting, I pulsed the inlet temperature for what I call Thermal Pulsing. I breakdown the profile, the roasts and the resulting performance where I found I prefer the taste of thermal pulsing over a regular Bean Temperature by Inlet Temperature (BT/IT) profile.
Roast Profiles
My baseline on the Roest has been the BT/IT profile created by Scott Rao. The inlet temperature is a function of the bean temperature. This is a comparison of how the baseline BT/IT profile operates compared to the Thermal Pulsing BT/IT profle:
Here is an example of the baseline profile in action:
This is an example of thermal pulsing where the inlet temperature is pulsed during the shot. The bean temperature still continues to rise, but it slows down periodically as shown by the Rate of Rise (RoR).
The one challenge I have with the profile is that a few cracks happen earlier which can set off the automatic bean drop. So I have to be careful, and I have been adjusting the profile accordingly.
Post-Roast Metrics
I looked at a few roast metrics to see if there were any interesting indicators, but most of the roasts seemed to be similar along all the data types.
I thought moisture would be more affected, and it seems like the moisture might be slightly raised using thermal pulsing, but that is inconclusive.
Coffee densities had a similar story.
Roast colors were all pretty much the same.
The one reasonable conclusion is that whatever differences are between have to deal with the profile as much of these variables are close to controlled.
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).
Data
I looked at 20 shots pairs across 6 roasts across a spread of time.
Thermal Pulsing improved taste over the baseline.
In terms of individual taste components, all saw an average improvement.
In terms of individual roasts, all roasts saw improvements with only a few shots without an improvement.
In terms of TDS and EY, the paired shots had about the same performance.
I also plotted Taste vs EY, which didn’t have too much of a trend. If anything, Thermal Pulsing pulled slightly lower in EY but had a better taste.
I looked at two-tailed paired t-tests for this data set to see if the differences were statistically significant. For taste, across all components and the average, the p-value was below 0.05 so they were all statistically significant improvements.
The slight decreases in TDS, EY, and IR were not statistically significant.
Thermal pulsing is an exciting discovery, and I’m particularly interested to see how further explorations go as I dive deeper into understanding why thermal pulsing improves taste.
If you like, follow me on Twitter, YouTube, and Instagram where I post videos of espresso shots on different machines and espresso related stuff. You can also find me on LinkedIn. You can also follow me on Medium and Subscribe.
Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
