Exercise 1 - solution

Blade grinders chop with spinning blades (20,000 to 30,000 rpm). The particles keep getting smaller the longer they run, so the result is a wide range of sizes plus coffee dust.

Burr grinders crush beans between two revolving abrasive elements; the gap between them sets the particle size, so the result is fairly uniform with less frictional heat.

Avoid a blade grinder for a pump espresso machine: the dust can clog the machine's sieves, and the article does not recommend it for that use.