by Jonathan Gagne
Now that I have outlined the method by which I pull espresso shots with the EG-1 grinder and SSP ultra-low-fines burrs (or ULF burrs for short), I thought it would be interesting to compare them with a more classical espresso grinder like the Niche Zero. I do not yet have great data to show you exactly how the particle size distributions of these two grinders differ, because doing so will require measuring the very-fine coffee particles down to a dozen microns in size, something extremely hard to do with imaging methods like my grind size application. Sifting might sound like a good method for this, but it is also impractical because, without a jet of pressurized air, fine particles tend to stick to larger ones, making it really hard to measure their contribution using sieve sets. Rather, I have plans to get some laser diffraction data for both grinders; it requires expensive machines, but it is a much better solution to detect the differences in how many fine particles different grinders generate.
We will see in this post how the differences in the shot characteristics between the two grinders strongly hint at a very different quantity of fines. You may recall from one of my earlier posts that a quantity often called D10 drives the hydraulic resistance of a coffee puck (i.e., how much it resists flow at a given pressure). Simply put, D10 is the size of the particle that you would encounter at 10% of the total dose weight if you sorted every particle by increasing weight. If we used D50 instead, and stopped at 50% of the total dose weight, we would get something called a “median” particle size (ordered by particle weight); it may be surprising that D10 and not something closer to D50 drives the puck resistance, but that is a consequence of fines having a disproportionate role in affecting the resistance.
With this in mind, you can understand how using a grinder that generates less fines will require grinding much finer overall to overcome the otherwise reduced proportion of fines, and obtain a similar puck resistance. I find it easiest to see this difference visually when inspecting the spent puck of a an SSP ULF shot (top panel below) to that of a Niche shot (bottom panel below), dialed in for similar puck resistances. In these photos, we can clearly see how the particles in the Niche spent puck are much coarser on average. I think it’s easier to see this effect in a spent puck because the fines get washed away to the bottom of the puck and in the shot of espresso, so we can more clearly see the coarser particles that remain. The SSP ULF shot at the top looks more like a uniform brownie, except where I damaged it when removing the filter paper.