How to Align Coffee Grinder Burrs: DIY Marker Test Guide

Burr alignment is the parallelism between the two grinding surfaces in your coffee grinder. Even fractions of a millimeter of misalignment cause one side of the burr set to cut closer than the other, producing an uneven particle size distribution — more fines on one side, more boulders on the other. The result is a cup where some particles are overextracted while others are underextracted, producing both sour and bitter flavors simultaneously even when your average extraction yield falls within the “ideal” range.

Hand-aligned grinders produce measurably tighter particle size distributions. Jonathan Gagne’s 300 PSD analysis across 24 grinders noted that “there is no way of knowing whether grinders are well aligned or not” without actually checking — burr alignment is a confounding variable that makes every comparison between grinders unreliable unless both are verified. Scott Rao identified divergent (non-parallel) burrs as the most common structural grinder problem, noting that even 1-2 ground coffee particles trapped under a burr during reseating can tilt it enough to degrade quality.

The good news is that checking and improving alignment is straightforward. The dry-erase marker test takes about 15 minutes and requires nothing more than a marker, aluminum foil, and a screwdriver. If you own a burr grinder — especially one you have upgraded with aftermarket burrs — checking alignment is one of the highest-impact things you can do for cup quality.

Why Alignment Matters More Than You Think

All grinders produce a distribution of particle sizes rather than uniform particles. This distribution is measured by key percentile values: D10 (10th percentile), D50 (median), and D90 (90th percentile). The span — calculated as (D90 - D10) / D50 — measures overall uniformity.

Here is the critical insight from Gagne’s research: the D10 value, not the average or median, determines the coffee bed’s hydraulic resistance. A particle 10 times smaller has 1,000 times less volume but enormously more surface area per unit mass. Fine particles extract faster, clog filters, and dominate flow resistance. When your burrs are misaligned, you get more fines from the tight side and more boulders from the wide side. The fines increase flow resistance and extraction on their portion of the bed, while the boulders underextract. Your grind size setting cannot compensate because the problem is not the average size — it is the spread.

For espresso, this matters enormously. Rao found that larger burrs produce narrower particle size distributions, fewer fines, and less heat damage than smaller burrs. A large-burr grinder can produce delicious 21% extraction yield espresso with minimal bitterness and astringency, while a small-burr grinder may cap out at 19.5% before the cup becomes unacceptable. That 1.5 percentage point gap translates to approximately 7% bean cost savings. But if the large burrs are misaligned, you throw away much of that advantage.

For pour-over and filter brewing, misalignment shows up as inconsistent draw-down times and a muddier cup. If your V60 brews vary wildly in total time despite identical dose, grind setting, and technique, misalignment is a likely culprit. For more on diagnosing extraction issues, see the channeling and uneven extraction guide.

The Three Structural Grinder Problems

Rao identified three categories of structural issues in grinders, listed from most to least common:

1. Divergent (non-parallel) burrs: The most frequent problem. The burr faces are not perfectly parallel, meaning one point of contact is tighter than the rest. This can happen from the factory, from worn mounting surfaces, or from particles trapped under the burr during reassembly. Even a tiny tilt — a few coffee particles’ worth — creates measurable unevenness in the grind.

2. Burr alignment offset: Some grinders have mounting holes slightly larger than the mounting screws, allowing the burr to shift up to 1-2 millimeters off-center. When the upper and lower burrs are not concentrically aligned, the cutting geometry changes around the circumference, producing inconsistent particle sizes.

3. Bent motor shaft: The motor shaft does not spin true, causing the burr to oscillate. This creates a cyclically varying gap between the burrs and an inconsistent grind. This is less common but also harder to fix — it usually requires professional service or motor replacement.

The marker test addresses the first two problems. A bent shaft requires a dial indicator to diagnose and is beyond DIY scope.

What You Need

• Dry-erase marker (any color that contrasts with your burr material — blue or red works well on steel)
• Aluminum foil (standard kitchen foil, not heavy-duty)
• Screwdriver or hex key to remove your upper burr carrier
• A cloth or paper towel
• 10-15 minutes

Optional but helpful: a flashlight or phone light to inspect the wipe pattern closely, and scissors for cutting precise foil shims.

Step 1: Clean and Inspect the Burrs

Remove the upper burr carrier according to your grinder’s instructions. Clean both burr surfaces thoroughly with a dry brush or compressed air. Remove any trapped grounds from the mounting area — this is important because even a few particles under the burr can create the tilt you are trying to fix.

Inspect the burr edges for visible chips, cracks, or excessive wear. If the cutting edges are rounded or damaged, alignment will not fix the fundamental problem — you need new burrs. Sharp burrs are the single most important grinder feature according to Rao, and as burrs dull, both fines and boulders increase simultaneously, always resulting in decreased flow rate and less extraction.

Step 2: Apply the Marker

Using the dry-erase marker, color the outer flat edge of the stationary (lower) burr. Cover the entire outer ring with a solid, even layer of ink. You want full coverage — do not leave gaps. The ink should be thick enough to be clearly visible but not so thick that it pools.

Some guides recommend marking the outer flat edge of the rotating (upper) burr instead. Either approach works. The principle is the same: you are creating a visual indicator that will be wiped away wherever the two burr surfaces make contact.

Step 3: Find the Chirp Point

Reassemble the upper burr carrier. With the grinder unplugged (for electric grinders) or the handle ready (for hand grinders), slowly close the grind adjustment toward the finest setting until you hear a faint chirp — the sound of the two burr surfaces just barely touching each other. This is the chirp point.

For electric grinders: Do this with the motor OFF. Turn the adjustment ring slowly and carefully by hand. You can feel and hear the burrs touch. Never run the motor with the burrs in contact — it damages the cutting edges.

For hand grinders: Turn the adjustment until you feel resistance when you try to rotate the handle. The first hint of resistance where the burrs engage is the chirp point.

Step 4: Read the Wipe Pattern

Remove the upper burr carrier again and examine the stationary burr where you applied the marker. The pattern of ink removal tells you exactly what is happening:

Full, even wipe around the entire circumference: Congratulations. Your burrs are well aligned. The surfaces are making uniform contact. No shimming needed.

Partial wipe — ink removed on one side, intact on the other: The burrs are tilted (non-parallel). The side where ink was wiped is the tight side. The opposite side where ink remains is the wide side. This is the most common finding and is what you will fix with shims.

Uneven or patchy wipe: Multiple high and low spots. This can indicate a warped mounting surface, inconsistent burr machining, or debris under the burr. Clean everything again and retest. If the pattern persists, shimming at multiple points may be needed.

No wipe at all: You did not reach the chirp point, or the marker layer was too thick. Reapply and try again, adjusting finer.

Step 5: Shim with Aluminum Foil

If the wipe pattern shows a tilt, you need to raise the low side. Standard kitchen aluminum foil is approximately 0.016 millimeters (16 microns) thick — thin enough for precise adjustments.

1. Cut a small strip of aluminum foil, roughly the size and shape of the gap between one mounting screw and the burr edge.
2. Remove the stationary burr (the one with the marker).
3. Place the foil strip under the burr on the low side — the side where the marker ink was NOT wiped away.
4. Reseat the burr and tighten the mounting screws.
5. Reapply the marker.
6. Reassemble and test the chirp point again.
7. Check the new wipe pattern.

One layer of foil may be enough. If the wipe is still uneven, add another layer. Typical corrections need 1-3 layers of foil (16-48 microns). Go slowly. Over-shimming flips the problem to the other side.

Step 6: Verify and Iterate

Repeat the marker test after each shimming adjustment until you achieve a full, even wipe around the entire circumference. This typically takes 2-4 iterations. Patience here directly translates to grind quality.

Once you have a clean full wipe:

1. Lock the burr mounting screws firmly. Shims should not shift during operation.
2. Run a small amount of coffee through the grinder to confirm the adjustment holds under actual grinding conditions.
3. Test the chirp point one final time — it should feel crisp and uniform rather than catching on one side.

Addressing Concentricity (Burr Offset)

If your grinder has mounting holes larger than the screws, the burr can shift laterally. The marker test primarily reveals parallelism (tilt), but concentricity issues also show up as uneven wipe patterns — specifically, a wipe that is tight on one side of the circumference and loose on the opposite side, even after shimming eliminates tilt.

To fix offset:

1. Loosen the mounting screws slightly — enough that the burr can shift but not rotate freely.
2. Tap the burr gently toward the side where the gap is widest (where ink was not wiped).
3. Retighten the screws.
4. Retest with the marker.

Some grinder modders use thin tape or Teflon thread seal tape on one side of the mounting holes to center the burrs and eliminate play. This is more permanent than relying on careful positioning alone.

Which Grinders Benefit Most

High-impact candidates:

• DF64 and similar 64mm flat platforms with aftermarket SSP burrs. The DF64’s stock mounting system has enough play that alignment checking after a burr swap is essentially mandatory.
• Eureka Mignon series. The mounting system is good but benefits from verification.
• Any grinder where you have recently replaced or reseated the burrs.
• Baratza Encore and Virtuoso after heavy use, where internal wear can introduce tilt.

Lower-impact candidates:

• Hand grinders like the Comandante C40, 1Zpresso JX-Pro, or Kinu M47. These typically have tighter tolerances from the factory, and the conical burr design is less sensitive to minor misalignment. Some hand grinder modders still align, but the gains are smaller. For more on hand grinder models, see the manual grinders guide.
• Grinders with precision-machined mounting systems (Lagom P64, Weber EG-1) that ship with factory alignment verified. Checking is still worthwhile but corrections are less likely to be needed.

After Alignment: What to Expect

A well-aligned grinder will show improvements in:

Consistency: Draw-down times for pour-over and shot times for espresso become more predictable. If your V60 brews previously ranged from 2:30 to 4:00 on the same recipe, alignment can tighten that to a narrow band. For espresso-specific dialing, see how to dial in espresso.

Clarity: With a narrower particle size distribution, you get less simultaneous over- and under-extraction. Flavors become cleaner and more distinct. The “muddy” or “confused” quality that comes from uneven extraction diminishes.

Extraction ceiling: You may be able to grind finer without stalling (for espresso) or without the cup becoming harsh (for filter). The tighter PSD means fewer fines clogging the bed at a given average grind size, giving you more room to push extraction before negative flavors appear. See the grind size micron chart for specific particle size ranges by brew method.

Reduced waste: Better extraction efficiency means more flavor from the same dose of coffee. Rao quantified this: the gap between a large-burr grinder at 21% yield and a small-burr grinder capped at 19.5% equals approximately 7% bean savings, roughly $0.80 per pound at $11 per pound. Alignment does not give you the same magnitude of improvement as a burr upgrade, but it moves your existing burrs closer to their theoretical performance.

The marker test is one of the simplest modifications in the coffee equipment world. Fifteen minutes and a dry-erase marker can meaningfully improve every cup your grinder produces. For the price of a marker and a few inches of aluminum foil, it is one of the highest return-on-investment adjustments available.