Every grinder produces a distribution rather than one size, so some variation is expected.
What is normal
Looking closely at burr-ground coffee, you will see a range around the target plus some visible fines.
Fines are produced when the bean fractures along its cell structure, and no grinder eliminates them. Around 5 to 15% by count is typical.
What is not normal
Obvious chunks — pieces several times the size of the majority — alongside powder.
That is the signature of:
A blade grinder, which smashes rather than cuts and cannot do better.
Dull or damaged burrs, which crush instead of shearing.
Misaligned burrs, where one side of the gap is wider than the other.
The marker test for alignment
Colour one burr face with a marker, grind briefly at a fine setting, and inspect. Even wear all round means aligned; wear on one side only means shimming is needed.
Judging by eye is limited
Particle distribution is properly measured by sieving or laser diffraction. The eye sees the large end of the distribution and misses the fines entirely.
Taste is the better test. Simultaneously sour and bitter means uneven grind, regardless of what it looks like.
The sieve test
Cheap kitchen sieves let you separate a sample and see the spread. Not laboratory grade, and informative — particularly for comparing two grinders.
Last reviewed 8 August 2026