Equipment
Burr Alignment And What Misalignment Costs
Grinder burrs that are not parallel produce particles of two different sizes at once, and the resulting uneven extraction is often mistaken for a coffee problem.
A grinder is judged by its burrs, but how those burrs sit relative to each other matters as much as what they are made of. Misalignment is common and its symptoms are easy to misread.
Grinding happens in a narrowing gap
Coffee enters between two burrs and is progressively broken down as it travels outward through a gap that narrows towards the exit.
The width of that gap at the outer edge determines the largest particle that can escape, which is what a grind setting actually adjusts.
The assumption behind the whole design is that the gap is the same all the way around the circumference.
Misalignment creates two grinders in one
If the burrs are not parallel, the gap is wider on one side than the other, so coffee exiting there is coarser than coffee exiting opposite.
The output is then a mixture of two populations rather than a single distribution centred on the setting you chose.
Because both populations are present in every dose, no adjustment of the setting can eliminate the split. Moving the dial shifts both halves together.
The cup shows contradictory faults
Coarse particles under-extract and contribute sourness and thin body, while fine particles over-extract and contribute bitterness and drying astringency.
Tasting both at once produces a cup that seems to need opposite corrections, which is the characteristic signature of the problem.
People generally respond by blaming the beans, the water or their technique, all of which are innocent in this case.
Causes are mostly mechanical tolerance
Burr carriers are held by threads, screws or a housing, and small manufacturing tolerances stack up into a measurable tilt.
Bearings with any play allow the rotating burr to wobble under load, so alignment can be acceptable at rest and poor while grinding.
Dropping a grinder or forcing a foreign object through it can also bend a carrier permanently, and the damage is invisible from outside.
Checking and correcting is straightforward in principle
A common check is to coat one burr lightly with marker ink and run the burrs together briefly at the point where they touch.
Even removal of the ink all the way around indicates parallel burrs; ink surviving on one side shows where the gap is larger.
Correction usually involves shimming the burr carrier with thin washers or foil until contact becomes even, which is fiddly but requires no specialist tooling.
