Why is my grinder producing uneven grounds?

Consistency is the hallmark of a great grinder. When your grinder produces uneven grounds—a mix of large boulders and excessive fines—it creates an extraction nightmare. Because different particle sizes extract at different rates, you end up with a cup that is simultaneously over-extracted (bitter) and under-extracted (sour). This lack of uniformity makes it nearly impossible to dial in a balanced recipe.

One of the most common causes of unevenness is burr wear. As burrs lose their sharpness, they stop cutting the beans cleanly and start tearing or crushing them. This mechanical degradation is a natural part of a grinder's life cycle, but it can be accelerated by grinding very hard, light-roast beans or by the presence of debris. If your burrs are visibly chipped or rounded, they are likely the source of your inconsistency.

Alignment is another critical factor. If the burrs are not perfectly parallel, one side of the bean will be ground finer than the other. This can happen due to manufacturing tolerances, physical impact, or improper reassembly after cleaning. Even a slight misalignment can lead to a 'bimodal' grind distribution, where you get two distinct peaks of particle sizes rather than a single, uniform grind.

Don't overlook the importance of cleanliness. A buildup of oils and fine particles inside the grind chamber can interfere with the flow of coffee and the movement of the burrs. If the adjustment collar is clogged with old, sticky coffee, it may not seat correctly, leading to 'drift' where the grind setting changes during operation. A thorough cleaning, following the manufacturer's guidelines, is often the first step in troubleshooting.

Finally, consider your technique. Feeding beans into the grinder too quickly can cause the motor to struggle or the burrs to shift, resulting in inconsistent output. If you are using a hopper, try to maintain a consistent weight of beans, or switch to single dosing to ensure the burrs are always working under the same load. In practice, if cleaning and alignment checks don't solve the issue, it is likely time to replace your burrs to restore the precision your coffee deserves.