Why does my grinder produce some very fine powder and some large chunks?

This is called bimodal distribution and is normal for conical burr grinders to a degree. Excessive bimodal distribution (visible chunks and powder in the same dose) usually indicates either dull burrs, a loose burr carrier, or bean channeling through the burr set. Check the burr carrier for wobble and consider replacing burrs if the grinder is over 3 years old with daily use.

Why do my espresso shot times vary by 5+ seconds between doses?

Extraction time variation of more than 3 to 4 seconds between doses from the same bean batch usually indicates inconsistent dose weight, inconsistent tamping pressure, inconsistent distribution, or grinder retention contaminating each dose with stale grounds. Rule out these variables before concluding the grinder is faulty.

How often should I clean my coffee grinder?

Light cleaning (brush out the chute and catch cup) every 1 to 2 weeks for daily users. Full burr cleaning (remove burrs, brush and wipe all surfaces) every 1 to 3 months depending on use volume. Oily dark-roasted beans require more frequent cleaning than light-roasted beans.

Can old burrs cause inconsistent grinding?

Yes. Burrs dull over time. A quality set of burrs lasts approximately 500 to 1000 kg of coffee (roughly 3 to 8 years of daily home use). Dull burrs produce more fines and more bimodal distribution. If the grinder is over 5 years old with daily use, burr replacement is the correct diagnostic step.

Coffee Grinder Not Grinding Consistently: 8 Causes and Fixes

If your coffee grinder produces uneven grinds, clumps, or wildly variable extraction times, the problem is diagnosable. We cover the 8 most common causes of inconsistent grinding and how to fix each one.

Step-by-Step Guide

Step 1: Check the bean type

Dark-roasted, oily beans produce inconsistent grinds in grinders designed for lighter roasts. The oil clogs burr grooves and causes clumping. If you recently switched to a darker roast, this is likely the cause. Clean the grinder thoroughly and consider a lighter roast bean.

Step 2: Check for static

Static electricity causes ground coffee to clump and stick to the catch cup and chute. Clumps produce uneven distribution in the portafilter or filter basket. Solution: the Ross Droplet Technique (RDT) — add 1 to 3 drops of water to the beans immediately before grinding. This eliminates static without affecting extraction.

Step 3: Check the grind setting

An excessively fine grind setting for espresso causes clumping as grounds compact inside the burr chamber. Move one setting coarser and check if clumping reduces. If you are grinding espresso, verify the setting is appropriate for your machine and portafilter basket.

Step 4: Clean the burrs and chute

Coffee oils accumulate on burrs and restrict the groove geometry. This produces more fines than clean burrs. Remove the upper burr carrier (consult your grinder's manual), brush all surfaces with a stiff bristle brush, and wipe with a dry cloth. Do not use water on burrs.

Step 5: Check the burr carrier for wobble

Hold the upper burr carrier and gently rock it. There should be no play or wobble. Wobble means the carrier is loose, which varies the burr gap with every grind cycle and produces inconsistent grinds. Tighten the carrier according to your grinder's manual. If the carrier continues to wobble, the bearings may be worn.

Step 6: Check the grind setting for slipping

Some grinders, particularly heavily used stepped models, have adjustment mechanisms that slip mid-grind from vibration. After setting the grind, grind 5 to 10 grams and verify the setting has not moved. If the setting slips, the adjustment ring or its detent mechanism is worn.

Step 7: Check retention for stale contamination

If your grinder retains 2 or more grams between doses, fresh doses are contaminated with stale grounds from the previous session. Purge 1 to 2 grams of fresh coffee before your dose to flush stale grounds. For serious single-dose espresso, switch to a low-retention grinder.

Step 8: Consider burr replacement

If the grinder is over 3 years old with heavy daily use, burr replacement is the correct long-term fix. Worn burrs produce excessive fines and wider particle distributions. For Baratza grinders, replacement burrs cost $30 to $50 and are a better investment than a new grinder.

Your espresso shot ran three seconds fast today and three seconds slow yesterday, same beans, same dose. That's not bad luck.

A coffee grinder not grinding consistently almost always points to one of a handful of diagnosable causes, not a machine that needs replacing.

Static buildup, a wobbling burr carrier, dull burrs, or retention mixing stale grounds into a fresh dose are the usual suspects behind uneven grinds and swinging shot times.

Some bimodal distribution, that mix of visible fine powder and larger chunks in one dose, is normal on conical burr grinders. It only becomes a problem when it's excessive.

Below, we cover all eight common causes, including how the Ross Droplet Technique fixes static clumping and when it's finally time to replace worn burrs instead of cleaning again.

Understanding What Consistency Actually Means

A coffee grinder grinds consistently when it produces the same particle size distribution across every dose. Consistency has two dimensions:

Dose-to-dose consistency: every 18g dose produces the same distribution as the previous dose. Measured by espresso extraction time variation — consistent grinds produce shots within 1 to 2 seconds of each other.

Within-dose consistency: every particle in a single dose is as close to the target size as the burr quality allows. Measured by particle size analysis (impractical at home) or by extraction quality.

Most home grinder problems are dose-to-dose inconsistency — the grinder works fine most of the time but produces occasionally wild shots. This is usually a retention, distribution, or static problem, not a burr quality problem.

Diagnosing by Symptom

Clumping in the catch cup: static electricity or oily dark-roasted beans. Fix: Ross Droplet Technique (add 1 to 3 drops of water to beans before grinding).

Wide variation in espresso extraction time (5+ seconds): retention contamination, inconsistent distribution, or dull burrs. Fix: purge before each dose, use a WDT tool for distribution, consider burr replacement.

Fine powder coating everything: burrs are set too fine, or burrs are dull and producing excessive fines. Fix: move one step coarser; if fines persist at correct settings, replace burrs.

Grinder sounds different than usual: a bean fragment or foreign object is stuck between burrs. Unplug, remove upper burr, clear obstruction with a brush.

Extraction times getting slower over weeks without changing settings: burrs are producing finer grinds as they dull. The dulling process changes the effective burr gap. Move the setting one position coarser and monitor. Plan burr replacement.

Cleaning Schedule for Daily Users

Component	How often	Method
Catch cup and chute	Weekly	Brush or wipe dry
Hopper	Monthly	Wipe with dry cloth
Burrs	Monthly	Brush with grinder brush
Full disassembly	Every 3 months	Brush, wipe, inspect for wear
Burr replacement	Every 3 to 8 years	Specific to grinder model

The Ross Droplet Technique (RDT)

Static is the most common cause of inconsistent ground coffee distribution, and RDT is the simplest fix.

Add 1 to 3 drops of water to your beans in the hopper or dose cup, stir briefly, then grind immediately. The trace moisture prevents static charge buildup on grounds. The quantity of water is small enough that it evaporates before reaching the burrs in most cases and does not measurably affect extraction.

Results: grounds fall cleanly into the portafilter or basket without clumping or static flyaways. Distribution is more even, which directly improves espresso extraction consistency.