Coffee Data Science
Espresso Volcano
More data on dialing in espresso
There is an idea that as one grinds finer, there is a drop off for extraction yield. As a result, there should be an optimal grind setting to maximize espresso extraction, and there is a drop off grinding coarser or finer. This is referred to as the volcano.
Lance Hedrick looked at this in a recent video, and I replotted his data. His plots were box plots, and for this small sample, I think plotting the data more verbosely is better.
Metric of Performance
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
He collected six shots across 8 grind settings. I sorted these shots, and plot them here as a line chart. The variance in EY increases as the grind setting goes higher, and the volcano effect does not look even on both sides.
He didn’t have particle distribution metrics, so it quite possible that the grind settings have an non-linear affect to particle distribution.
However, we can still look at the median EY, which shows a nice slope.
This is not a great volcano.
However, if we look at the minimum EY, we see something closer to a volcano shape.
Looking back to my own data, I thought the lack of a volcano was due in part to thermal pre-infusion. I didn’t see an extreme downward trend towards a finer grind, but towards a coarser grind, I started to see one.
These findings point to the idea that you can get close to some maximum, but grinding finer will error on being in the right range.
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
