Three factors – sharpness, size, and alignment – have a big effect on grind size distribution. Worn, blunt burrs tend to ‘crush’ the beans with compression stress rather than ‘cut’ them with shear stress. As discussed in Lesson 1.02, compression forces cause the particles to break up into randomly sized fragments, so blunt burrs produce widely spread particle size distributions, resulting in less even extraction.
Larger burrs seem to generally produce more even grind size distributions,