Coffee Data Science

Dropping Some Pulses during Coffee Roasting

Examining the beginning and ending

Robert McKeon Aloe
4 min readAug 6, 2024

Diving into thermal pulsing, I have been removing parts from the roast profile to better understand how it works. Initial tests in dropping some of the pulses entirely were interesting. So I explored with taste.

Thermal Pulsing Variants

Here is the baseline Bean Temperature/Inlet Temperature (BT/IT) profile and thermal pulsing.

I dropped the last two pulses, but it looks like I just dropped one; it just went flat.

This dropped the first two pulses, but it looks like there is an extra pulse because of the second half starting on a drop in temperature.

Roast Statistics

Most of the post-roast measurements showed similar readings except for water activity.

Weight loss was pretty similar.

Moisture didn’t move much.

Water activity was very different. I’m not sure what exactly that means or rather if it is predictive or not.

Color level was on point.

The same was true for density.

Tasting Equipment/Technique

Espresso Machine: Decent Espresso Machine, Thermal Pre-infusion

Coffee Grinder: Zerno

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 pulled four shots for each roast, which is enough to give some intuition at how the different changes affect taste. My goal is to understand what is the most important in a thermal pulsing profile.

EY was about even across the shots.

These tests suggest dropping pulses doesn’t necessarily help. If you squint, it looks likes dropping pulses negatively effects taste, but really, the difference doesn’t look like much. I should try dropping the middle two together and separately. I also want to test the maillard reaction because I suspect I am elongating the reaction, but I would like to do that in a more controlled way (or maybe just less complicated).

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

My Links

Collection of Espresso Articles

A Collection of Work and School Stories

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Robert McKeon Aloe

I’m in love with my Wife, my Kids, Espresso, Data Science, tomatoes, cooking, engineering, talking, family, Paris, and Italy, not necessarily in that order.