Coffee Data Science
Swinging the Coffee Roast at the End
More thermal pulsing explorations
As my initial investigations have turned out well, my investigations have shifted into more nuanced parts of the roast. I have started to look at the beginning, middle, and end separately to tease out optimizations. This investigation is looking at the last minute of development particularly what happens with an upswing or a downswing.
Roast Profiles
The baseline profile is the thermal pulsing profile, and I modify the very end.
Zooming on the last 20 degrees of the roast profile, the differences start to show.
The profiles all tracked similarly with the baseline being slightly shifted in time.
The same is true with the Rate of Rise (RoR). The thermal pulsing profile has an increase in the RoR at the end because of the upswing, and I’m not sure how helpful that metric is aside from not dropping below 0. In this case, the downswing simply keeps dropping.
Post-Roast Metrics
The roasts were pretty close in their metrics, but they had weird places where there were matches. The downswing lost more weight than the other two.
Moisture levels were essentially the same.
Water activity was lower for the downswing, but I’m still unsure how important water activity is post-roast. This could also have been related to time in some way because the downswing was the last roast, so the other two had 15 to 30 minutes to increase in water activity. I’m not sure how quickly water activity changes.
For roast color, downswing and upswing matched better. A 7 point difference isn’t huge, but it might be noticeable in taste.
Density was about the same.
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 pulled 4 shots per roast, and the aim is to get some intuition on whether one of these modifications leads to a great improvement or degradation in taste. As it turns out, neither upswing or downswing tasted better.
The downswing roast, in particular, tasted baked. I have tried multiple times to make a baked roast where I could really taste it, and I happened to have found it here. The taste was very muted, not sweet, and muddy.
I thought there might be influence in roast development, but the flavor muting was odd. Even the upswing was not great, and I had suspected the upswing would taste more bitter, but in my scoring, I didn’t notice much of a difference.
All these shots had similar Extraction Yield (EY), so I don’t think there was an influence based extraction efficiency.
This experiment has set more firmly in my mind that the end of the roast should not have major changes. I wonder if rapid temperature pulsing would be of interest but that might be difficult because the heat of the drum and the beans won’t change that quickly in the one minute of development time.
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
