Coffee Data Science
Measuring Coffee Fines Using Water
A fun approach inspired by forced fines migration
While thinking about my forced fines migration experiment, I thought it would be an interesting way to measure fines throughout the puck. You could measure fines using imaging or sifting, but both have some challenges. For imaging, you can’t resolve the smallest fines. For sifting, it is challenging to sift below 200um or even below 300um without great effort.
With my forced fines migration experiment, I was able to push out all the particles finer than the filter basket holes. I thought I could then dry the sample and have a better measurement of fines.
Puck Preparation
I used 22g in a 20g VST basket, and I pulled 8:1 shot with 27% EY measured using an Atago, so most of the extractable coffee had been pulled out. Then I let the puck cool.
Afterwards, I sliced it up. I was aiming for more than 3 slices, but it was difficult. I ended up with a slice of the bottom, a slice in the middle, and the top was split into two samples.
I put the slices in an ice cube tray, my preferred way of storing grounds.
Then I pushed some water through to force the finer particles to migrate through the filter basket.
Here is a video reviewing how I can force fines to migrate, which is essentially a wet sifting.
In the process, there were a lot of suspended particles.
I let them settle, and I removed the water. I dried the samples in the oven at a low temperature.
The resulting fines were much finer than regular coffee sifted with a fine sieve.
I ended up with coarse and fines for each of the four samples.
I then weighed each sample using an Acaia Pyxis scale, and I calculated the percent of of fines in each sample.
I expected if fines migrated in the original shot, the bottom would have a higher percentage of fines than the other layers. However, this was not the case.
I’m not sure why the fines were higher in the top layers, and this could have been a mistake in the measurement, the cutting, or the forced migration process. Some fines might have migrated out of the shot, but the amount of fines that come out in the shot turns out to be less than 0.01g (experiment to come).
Ultimately, this experiment is another mark against the theory of fines migration, and it provides an experiment that is easily repeatable. The trouble with previous experiments was knowing if you had truly gotten all of the finer particles. Wet sifting seems to help measuring the finest of the fines.
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