Coffee Data Science
Fan Pulsing for Coffee Roasting Continued
Fan out of phase with heat
In looking at thermal pulsing, I started with a constant fan speed. Then I looked at pulsing the fan speed particularly by setting the fan high when the inlet temperature went high or low. I found initially that the Fan High on Down (or low) showed some signs of doing better than the baseline. So I did a few more roasts to evaluate the profile further; all roasts done on the Roest.
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.
I roasted four coffees (two Ethiopian coffees and two Guatemalan coffees) using a baseline thermal pulsing and Fan High on Down.
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
I ended up with 16 pairs of shots. The performance benefit was clearer on the Ethiopian coffees than the Guatemalan.
The taste scores for the sour and bitter components did better than the baseline.
The TDS and EY seemed lower, but there was not a statistical difference for this sample size.
Overall, the taste metrics had a difference, particularly Sour and Bitter as well as the Final Score.
This profile encourages me to explore further into pulsing the fan and modifying the heat possibly along the lines of convection and conduction. I want to explore switching out how the beans are heated, and I suspect using drum temperature would be super helpful to understanding how the beans roast.
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
