What is burr alignment? Does it matter for a home grinder?

What happens when burrs are misaligned?

Misaligned burrs leave an uneven gap, which spreads out the particle sizes. Espresso Aficionados says misalignment leads to "uneven particle sizes and reduced grind uniformity."

Coffee Navigated, drawing on practitioners and earlier research, says poor alignment can give both over- and under-extracted coffee in the same cup. It describes the taste as a mix of bitterness and sourness.

Counter Culture Coffee adds that misalignment causes inconsistent particle sizes and can damage the grinder. Perfect Daily Grind notes that larger burrs need more precise alignment, which is one reason the topic comes up most with large flat burrs.

How do you check burr alignment?

The most common check is the marker test. Espresso Aficionados describes coloring the flat edge of a burr with marker, reinstalling it, then bringing the burrs together until they just touch.

If the ink is wiped off all the way around, called a "full wipe," the burr is square to the axis. A wipe on only one part means a high spot. Coffee Navigated describes the same whiteboard-marker method.

Two other checks exist. Espresso Aficionados suggests measuring the distance between the first chirp and the point where the burrs lock, where a smaller distance suggests better alignment. Coffee Navigated describes listening for a single touch per rotation, which points to a misaligned set.

How do you fix burr alignment?

Alignment is usually fixed with thin shims under the burr, or by machining the mounting surface. Espresso Aficionados says to place shims under the screw opposite the high point, repeating until you get a full wipe.

A guest post by Mitchell Hale on Scott Rao's blog describes a different method: sanding the burr carriers so the burrs seat flat without shims. It warns that afterward "your zero will change significantly," because material has been removed from both mounting surfaces.

Either way, you will need to find your grinder's zero point again and recalibrate. Your old settings, and any settings chart you were using, will no longer line up until you do.

Does burr alignment actually change the taste?

This is contested, and the honest answer is "probably somewhat, but it is hard to prove." Espresso Aficionados says the taste improvement is "generally considered difficult to prove," and suggests the main benefit may be peace of mind.

The same guide does report one observable effect: after alignment, people often notice the espresso puck withstands higher pressure at the same grind setting. Coffee Navigated argues that more uniform particle sizes give clearer taste and aroma.

Coffee ad Astra, after measuring 24 espresso grinders, noted it had no way of knowing whether they were well aligned. It said alignment "could plausibly affect" both uniformity and unimodality, which is exactly why the question stays open.

Do new grinders come aligned from the factory?

Not always, according to Scott Rao. He wrote that of more than 100 Mahlkönig EK grinders he had used, he estimated "at most 10%" were well aligned out of the box.

That is one person's estimate about one commercial model, not a survey of home grinders. Still, it is a reason to favor grinders with a reputation for consistent build quality and manufacturer support.

Should alignment decide which grinder I buy?

For most home brewers, alignment should be a tiebreaker rather than a deciding factor. Burr design, adjustment and support usually matter more day to day.

Where it can tip the balance is with large flat burr grinders, where Perfect Daily Grind says alignment demands are higher. If you are cross-shopping a flat burr single-dose grinder against a conical one, as in DF64 Gen 2 vs Niche Zero, it is worth asking owners how consistent their units are.