Titan Grinder Project: Particle size distributions of ground coffee - Page 2

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artichoke

#11: Post by artichoke » Sep 01, 2010, 4:17 pm

RapidCoffee wrote:I tried to keep everything as standard as possible in Excel, so the X units are particle "diameter" and the Y units are the percentage of the total particles. As I understand it (and please be aware that my understanding of the machine is limited), the raw data measurements are associated with diffraction of a laser beam that passes through the particles. Assumptions are entered for the refractive index of the liquid (for wet analyses) and the particle characteristics (spherical vs. irregular shape, transparent vs. absorbing, etc.). Then special formulas (aka "magic") are used to translate these light measurements into particle number, surface area, and volume.
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EDIT:
The MicroTrac manual indicates that the particle volume distribution is generated first, and surface area and particle number are derived from that. The X axis label represents the particle "diameter" in microns, in this case also derived from the volume distribution. I'm putting diameter in quotes because it's not a well-defined quantity unless the particles are assumed to be spherical.

Hope this helps.
Not to be picky, but what assumption did you use for the particle shape -- spherical, or how irregular? I imagine this could differ among grinders, and conical vs. flat burrs. I've heard people say that some grinder seems to make nice "flakes" which they seem to think are advantageous.

And even for a given degree of irregularity, if that is defined as (radius / surface area) or (radius / volume), there could be different brewing performance. Flat flakes could pack tightly together and provide more flow resistance than random 3-d shapes in the puck, I think. So the analysis cannot account completely for puck-performance, but it surely is helpful!

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another_jim
Team HB

#12: Post by another_jim » Sep 01, 2010, 4:55 pm

artichoke wrote:Not to be picky, but what assumption did you use for the particle shape -- I've heard people say that some grinder seems to make nice "flakes" which they seem to think are advantageous.
With John, there were no assumptions, and no BS, just SEM :D
Jim Schulman