Burrs must sit parallel to grind evenly. If one side of the gap is narrower than the other, coffee is ground at two different sizes at once.
Why it happens
Manufacturing tolerances. Burr carriers, mounting faces and shafts each have tolerances, and they stack.
Even well-regarded grinders ship misaligned surprisingly often. It is not a defect so much as an economic decision — perfect alignment costs money.
What it does
Widens the particle distribution. Effectively the grinder has a range of gaps rather than one, producing exactly the fines-and-boulders spread that uniformity is meant to avoid.
Reduces the usable fine range. A misaligned grinder chirps — burrs touching on one side — before it reaches espresso fineness.
How to test
The marker test. Colour the flat face of one burr with a marker, run the grinder briefly at a very fine setting, and remove the burr.
Even wear all the way round — aligned. Marker removed on one side only — misaligned.
How to fix it
Shimming. Thin washers or foil shims under the burr carrier on the low side, adjusted until the marker test comes out even.
It is fiddly, iterative, and free apart from the shim material.
Is it worth doing
On a grinder you already own and intend to keep, yes — it is the cheapest real improvement available.
The alternative
Grinders with machined alignment features and tighter tolerances. That is a large part of what the price difference buys at the high end.
Last reviewed 8 August 2026