Coffee Data Science
Fan Pulsing during Thermal Pulsing for Coffee Roasting
A broad search to combine fan modulation and heat modulation
Recently, I found thermal pulsing to produce a better roast than a more traditional roast curve. To take this concept a step forward, I wanted to see how fan modulation could be used during this process. High fan speeds allow for faster heat absorption, so this could be used to influence a pulsed profile so I did three variants on the Roest:
- Baseline thermal pulsing
- Thermal pulsing setting the fan high when the pulse wave hits a low point
- Thermal pulsing setting the fan high when the pulse wave hits a high point
Roast Variants
This is an example of pressure pulsing where the inlet temperature is pulsed causing the Rate of Rise (RoR) to pulse. The fan speed is at a constant 75%.
Fan High on Down means the fan is maxed out at 100% when the pulse hits a low, and then the fan speed is decreased when the pulse hits a high point. In theory, this should speed up heat absorption on the lows and decrease it on the highs. The fan speed pulse is 180 degrees out of phase with the heat pulse.
Fan High on Up means the fan speed is high when the pulse hits a high. So the fan speed trends with the heat pulse.
This shows all three fan speeds throughout the time of the roasts.
Both of these had an offset to the baseline in the roasting curves. I suspect this is due to the drum not being at the right temperature for the first roast. I have been doing more work to control for batch-to-batch parameters for consistency.
Rate of Rise (RoR) shows a phase shift, and most of the baseline lines up with Fan High on Down until the last two pulses.
Both fan variants had slightly more cracks, but they had similar trends in how quickly the cracks occurred.
Post-Roast Statistics
The weight loss was pretty similar for the roasts.
The moisture was higher for the Fan High on Up.
However, water activity was down for Fan High on Up.
All had similar roast color.
The density was also similar.
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
For this feasibility study, I had four shots per each variant. Thermal Pulsing (TP) Fan High on Up under-performed the other two roasts. It tasted darker than it was. TP Fan High on Down was slightly better in taste.
In extraction yield, the shots were similar except for the first TP Fan High on Up, which may have contributed to a lower taste score.
For me, this feasibility experiment eliminates Fan High on Up as an option at the moment. However, I am interested to test Fan High on Down, so I did a few more roasts to give a broader dataset on the topic.
One challenge I had with both of these was that the crack on the Roest detection catches a few extra cracks so then I have to watch these more manually to make sure it doesn’t drop my beans before they are done. I could make an adjustment to my settings as well, but it was something to be aware of.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
