Three factors – sharpness, size, and alignment – have a big effect on توزيع حجم الطحن. Worn, blunt التروس tend to ‘crush’ the beans with الضغط stress rather than ‘cut’ them with shear stress. As discussed in Lesson 1.02, الضغط forces cause the particles to break up into randomly sized fragments, so blunt التروس produce widely spread particle size distributions, resulting in less even extraction.
Larger التروس seem to generally produce more even grind size distributions, and they grind faster and are less prone to getting hot.
Aligning التروس so that they are perfectly parallel also has a dramatic effect on توزيع حجم الطحن and coffee quality. If the التروس are not properly aligned, then particles of different sizes can escape from different parts of the التروس and the grind size will be much less uniform.
The effect on توزيع حجم الطحن can be seen in this graph, which shows the grind size distributions produced by two different Mahlkoenig EK43 grinders. The line in blue is the distribution from a grinder with properly aligned التروس, while the distribution in grey, from a less well aligned grinder, shows two distinct peaks.
A comparison of grind size distributions of two EK43 grinders. Source: https://www.nature.com
End Æ 2.01