Burr Alignment
Burr alignment refers to how precisely parallel and concentric a grinder's two burr surfaces are relative to each other. In a perfectly aligned grinder, the gap between the stationary burr and the rotating burr is exactly uniform at every point around the circumference. This uniformity ensures that every coffee particle is cut to the same size as it passes between the burrs. Even small misalignments — measured in fractions of a millimeter — can produce noticeably uneven grinds with excessive fines and boulders that degrade extraction quality.
Misalignment can be caused by manufacturing tolerances (the grinder wasn't perfectly aligned at the factory), wear over time, improper reassembly after cleaning, or physical impacts (dropping the grinder or bumping the burr carrier). The symptoms of misalignment include: inconsistent grind size even when the setting hasn't changed, one side of the burr wearing faster than the other, difficulty achieving even extraction (channeling in espresso, uneven drawdown in pour-over), and the inability to grind fine enough for espresso without choking.
Checking alignment typically involves removing the top burr set and examining the contact pattern between the burrs when they are brought together at the finest setting. A dry-erase marker test is a common DIY method: color the face of one burr with marker, reassemble, spin the grinder briefly at the finest setting, and examine the contact pattern. If the marker is removed uniformly across the entire burr face, alignment is good. If only part of the face shows contact, the burrs are misaligned.
Correcting alignment is an advanced procedure that may involve shimming the burr carrier with aluminum foil, adjusting mounting screws, or using aftermarket alignment tools. For flat burr grinders, companies like SSP and Titus sell precision-machined alignment tools specific to popular grinder models. Many home baristas find that even modest alignment improvements produce noticeably better grind quality and more consistent espresso shots. However, if you are not comfortable with precision mechanical work, a professional grinder service can perform alignment for you.