Coffee Data Science
Roaster Charge Temperature
The start of a more focused charge temperature
Charge temperature is the starting inlet temperature of a coffee roaster. Many roasters have different opinions on optimal charge for all coffees, some coffees, or multi-batch coffee strategies. To explore this variable, I’m starting very broadly and expanding use three charge temperatures:
- 100 C Charge
- 191 C Charge (current baseline)
- 300 C charge
Post-Roast metrics
The weight loss went up a little for the hotter charge, but the density was similar between all three.
Moisture is constant, and the roast color is pretty close.
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).
Shots
I pulled four shot pairs to give some insight but not definitive answers. 300 C charge under performs all the time, and 100 C charge under performs some of the time.
This is clearly when re-sorting the shot data.
For EY, the results are all similar.
From this experiment, I’m going to squeeze the charge range to 150 C, 191 C, and 250 C. My hope is to find a good charge setting and then expand the comparison across a few coffees to confirm.
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
