Comparing Laser Diffraction to Imaging of Coffee Particles | by Robert McKeon Aloe | Apr, 2023

Espresso Knowledge Science

Splitting beans

For the previous two years, I’ve been measuring coffee ground distributions using imaging. This has been so helpful in diving deeper into what’s going on with a espresso grinder, and I actually loved the problem of the picture processing required. Nonetheless, I used to be at all times curious how these measurements in comparison with laser diffraction. Laser diffraction is often very costly, however I had a possibility to run a couple of samples and examine to my technique.

Laser diffraction for particle distribution makes use of a laser and a diffraction grating to extra precisely measure small particles. It outputs the typical diameter of the particle, and a typical laser particle analyzer makes use of a feed tube to measure particles sequentially. A chance distribution is then made primarily based on the amount of the particles. These machines price round $100,000, which isn’t economical for espresso interest explorations.

Espresso particles can be measured utilizing imaging. This entails placing a pattern of espresso on a bit of paper, spreading out / declumping the espresso grounds, and taking a calibrated picture. A calibrated picture means the picture aircraft can translate to an actual measurement of measurement.

I actually like having the ability to do form evaluation, and I believe that’s extra informative than particle diameter. Nonetheless, I might like to have each the excessive accuracy of laser imaging and the particle form data from digital camera imaging.

Let’s take a look at some knowledge. I’ve each floor espresso and spent espresso. Spent espresso clumps a lot much less, however it’s not at all times consultant of the grinder.

In all of the bins, it’s clear that the cumulative distribution cannot be checked out with out eradicating the decrease bins for the laser approach. On this approach there’s extra alignment, however a greater check may have additionally sifted the espresso grounds to have the ability to insure the measurement between laser and imaging was the identical particle sort.

In my normal imaging measurement, I exploit the minimal diameter as that’s what a sifter will measure. Nonetheless, to get nearer to the lasered measurement, I checked out minimal and common diameter. The common diameter appears to suit a bit higher for bigger particles over 100um, however the minimal diameter suits higher for particles lower than 100um.

I’ll keep on with common diameter as a result of that’s nearer to what the laser measurement is offering. I can take a look at a grind earlier than and after the shot. The imaged knowledge reveals the post-shot particles get somewhat finer whereas the lasered reveals the other. I ponder if that is tied to the accuracy on the decrease readings.

I plotted the cumulative % of particles in opposition to one another, and this may be a flat line in the event that they have been the identical.

These outcomes nonetheless present a niche in efficiency, however imaging is seemingly inside vary of lasered knowledge. I don’t normally examine these distributions to laser diffraction measurements, so inside the similar technique, the variables are extra managed than evaluating to a different measurement sort.

I nonetheless desire to have the precision of the laser measurement for the 3D form in addition to the precise 3D form to raised perceive a grinder, and which will at some point occur if somebody made a desktop laser diffraction particle analyzer.