For many years I have worked on old ultra high quality research microscopes and restored them with the goal of making them at least as good as they were when new. I have always considered the Leitz Orthoplan to be (easily) the best optical microscope ever manufactured. I have restored two of these, one made in 1969 the other 1981. The Orthoplan is modular, and my two instruments have somewhat different modules at this point. The newer one is mostly set up for fluorescence and phase contrast, and the older one for bright field and oil immersion dark field.

Optical microscopy is limited by the wavelength of light. I decided to try to examine two different coffee beverages with dark field oil immersion. For the images below I used a Leitz 40x 0.95 apochromatic objective with a special oil immersion condenser.

The first image is of a freshly pulled shot of espresso made with my 1999 La Pavoni Europiccola. Because the coffee is liquid the small particles in it are subject to severe Brownian movement. The depth of field is very limited. The visual impression using 10x oculars is amazing. There is a sea of bubbles, and then there are very many particles near the limits of optical detection. The small particles are bouncing around from Brownian movement, and most are not in the plane of sharp focus that presents severe problems capturing them in an image. (If you divide the width of the image below on your screen in millimetres by 12, and then multiply that number by 40 you will get magnification that you observe. On my monitor HB images are about 280mm wide. This corresponds to about 1000X overall magnification.) Colour images consist of a red, a green, and a blue component. The image shown is monochrome and shows the BLUE component, because resolution is significantly higher for shorter wave length light.



Note all bubbles, because the light that is illuminating them comes from a ring source, the bubbles have a ring like appearance. Much smaller than the bubbles are the sea of particles undergoing Brownian movement. Some that happen to be near the plane of focus are fairly sharp, considering they are about 1000X magnified on your screen! The "live" visual appearance of espresso observed this way is striking. All the tiny particles are "jumping around".

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After I examined espresso with this set up I made a slide with my cold brewed coffee. The identical optical set up was used as above. The visual appearance is strikingly different. There are almost no tiny particles. There are few bubbles. What there here are small "chunks" that look like ultra tiny rocks.



The tiny "rocks" are spread quite evenly in the sample. Interestingly enough they are mostly very similar in size. The sea of tiny particles undergoing Brownian movement is absent.

rpavlis wrote:There is a sea of bubbles, and then there are very many particles near the limits of optical detection.

That's a pretty interesting description of espresso, observed at extensive magnification. Thanks for sharing this, pretty interesting seeing how different coffee is from different types of brewing. I wonder how brew methods like siphon, moka pot ext would look.

Here is an image of Turkish coffee, same parameters as earlier. At this power it looks like a rock pile!

Wow, great description, those pictures are very informative. Expanded my knowledge, thanks

I can't see much myself in the images, but it was interesting to read your qualitative description!

Wow!!! Your images are really cool....!
I see that you've mentioned that one of your 'scopes does fluorescence (epi?). (I have enormous respect for Leitz instruments, but have been a Zeiss guy for many years....)
Have you tried staining your coffee to selectively light up particles as a way to complement your dark field work?

Also, what you've written about ImageJ is right on--Wayne Rasband should get a Nobel Prize for his work; years ago, we advanced the precursor of ImageJ--NIH Image--to do 16 bit operations.

I've also very much enjoyed reading your thoughtful work here on HB to image coffee grounds--great studies you've done--surprisingly hard thing to do, as you well-know, especially for gauging shape.

Good to see scientists like yourself writing about their coffee explorations.....