Coffee Data Science
Post-Espresso Shot Coffee Particle Distribution
A peek into how extraction affects particle size
As I have been looking at particle distribution, I got curious about after the shot. How does extraction change particle sizes? Does extraction shrink coffee?
Luckily, I pull layered shots, and I’ve been pulling sudo-staccato shots recently using a Niche grinder. Additionally, I use a cloth filter between the fine and coarse layers, making them easier to separate.
I took pulled some shots, and the only trick was to separate the coarse (Setting 30 or S30) and mid (Setting 15 or S15) layers. However, a little spoon solved the problem.
Here are all the plots combined, but I also separated them further below.
For Setting 0, the peak didn’t shift much, but everything else got finer.
For setting 15, the shift was clear across the board.
Same for Setting 30:
The differences for the cumulative distributions are shown below:
Flip the Axes
We can flip the X and Y axes, and look at how do the distributions shift as illustrated below. I assume particles shrink, and that might be a good approximation to extraction.
I did this by doing a best fit polynomial to each particle distribution. Then I could calculate the shift in the cumulative volume pre and post shot. For example, I could see how in the graph above, 50% of particles have a diameter less than ~340um, and post-shot, 50% of particles are around ~280um in diameter.
One could view the percent of diameter change post-shot as the extraction, but I’m not sure how well that aligns. In that view, it looks like there is a peak extraction occurring where particles above or below don’t shift as much.
However, I don’t want to assume a particle of a certain diameter evenly extracts compares to other sized particles. The high values in this graph at the lower % volume are due to the uncertainty of measurement.
This experiment was very straight-forward, and the particle distribution matched my expectations. I’m not sure what could be done with this information aside from general confirmation, and it is another piece in the puzzle that may come in handy one day.
If you like, follow me on Twitter and YouTube 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.
Further readings of mine:
Collection of Espresso Articles
A Collection of Work and School Stories
Measuring Coffee Grind Particle Distribution using Image Processing
Improving Coffee Grind Measurement using a Sifter
Measuring Fines in Coffee Grounds using Advanced Image Processing
Improving Coffee Grind Distribution using Adaptive Thresholds
Photographing Coffee Grounds for Grind Distribution Analysis