Grind consistency refers to how uniform the coffee particles are after grinding. When a grinder’s burrs are dull, misaligned, or improperly calibrated, the result is a mix of particle sizes rather than a consistent grind. Water finds the path of least resistance through larger particles while over-extracting the finer ones, so you end up with a shot that’s simultaneously under-extracted and over-extracted. That’s often exactly what produces the sour-and-bitter combination; baristas struggle to dial out even after adjusting dose and tamp pressure.
Calibration is the process of making sure the grinder’s settings actually correspond to a predictable, repeatable particle size, and that this stays true as burrs wear down. Burrs are consumable parts. Depending on grinder type and daily volume, commercial burrs typically need replacement somewhere between 300 and 1,000 pounds of coffee ground through them. As burrs dull, they don’t fail all at once, they gradually shift toward producing more fine particles and dust, which changes extraction even if nobody touches a single dial.
This is why a grinder that worked beautifully six months ago can start producing muddy, inconsistent shots today, without anyone changing the recipe, the beans, or the settings. The grinder itself has changed underneath the barista.
A proper calibration check involves pulling test shots at a known dose and time, examining the grind for uniformity, and adjusting burr alignment and gap settings until extraction lands in the expected range consistently, shot after shot. For a busy cafe, this isn’t a one-time setup task, it’s an ongoing part of equipment care that belongs on the same maintenance schedule as descaling and seal replacement.
The takeaway for any cafe owner: if shots have gotten inconsistent, look at grinder calibration and burr wear before assuming it’s a technique problem or a bean problem. Sometimes the fix isn’t a new grinder at all, it’s simply recalibrating the one you already have.