Coffee is Not Round

A Microscopic View

7 min readMay 15, 2020

A year ago, I looked at coffee particle distribution using photography. The analysis perplexed me because it was difficult to resolve particles smaller than 100um (100um in diameter was 2 x 2 pixels in my image). The other difficult part was understanding the particle shape. As I continued to work on understanding particle shape, I decided to buy a cheap microscope and look a little deeper.

I want to let pictures explain my experience, and the summary is that a microscope gave me a whole new way to view coffee. Ultimately, coffee grounds are not round, and I have to change the way I look at particle size and distribution because maybe the shapes of the particles matter more.

Others have looked at coffee through a microscope, and I’m not sure why a bigger discussion has not been had because particle shape should also impact computer models simulating water flow through espresso.

Using images to measure distribution

Left: Staccato Espresso layers. Right: Coarse grounds only.

Green Bean

Roasted Coffee Bean

Coffee Grounds

More coffee grounds:

Espresso Liquid

Salt as a Crystal Reference

Coffee Stain from a drop of coffee that dried

I sifted grounds, and I made a staccato shot. Then I was able to look at each layer using the microscope.

Fine Grounds (<400 um)

Mid Grounds (400 um < Mid < 500 um)

Coarse Grounds (> 500 um)

Flour as a Reference

Kruve Sifter holes close up

Bottom of the Puck, Post Shot

Here are the dark spots up close which show actual tunnels or they are sealed by coffee that dried.

Filter Basket Holes from the Bottom of the filter

Moldy Coffee

I have more of an appreciation for what happens at the microscopic scale. This visualization helps me better to understand that modeling coffee particles as crystals is better than as spheres, at least for me. My current modeling is based on density rather than individual particles.

One clearer conclusion is that coffee grounds don’t clog the filter because by each filter hole is a hole in the coffee. I’d be curious if someone found a case where the filter clogs, to see a microscopic view of it. That doesn’t mean the filter doesn’t cause channeling, but the channeling seems more likely caused by the filter hole distribution itself.

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.