A grinder never produces one particle size. It produces a spread, and the shape of that spread (how many fines, where the main peak sits, how many oversized "boulders") is what makes two grinders at the "same" setting taste different. This page collects what Lance Hedrick says about that spread, including boulders, unimodal vs bimodal, and the clarity vs body trade-off.
What a particle size distribution (PSD) is
- A PSD sorts grounds into size bins and reports how much falls in each, by count or by volume 1:32. Counted by number, fines always dominate the chart, which is why published graphs are usually by volume 3:35 7:42.
- Moving the burrs shifts the main peak coarser or finer. The large population of tiny particles is there whatever you set 7:42.
- Burr gap isn't particle size. A 500 µm gap produces particles around 600 to 650 µm because grounds are elongated and some slip past the burr edges 6:06.
- Particle shape matters too. Elongated grounds extract to their core faster than round ones, so shape can change flavour even when the size chart looks the same 3:36.
- The first grams out of a grinder are coarser than the rest, because beans jam up as the dose goes through 3:36 (see slow feeding).
Fines
Definition. There's no fixed cut-off. Lance Hedrick has used "under 200 µm" 7:36, "under roughly 50 to 100 µm" 3:36, and points out that 90, 150 or 200 µm are all arbitrary choices 24:01.
What they do in the cup
- Fines have a lot of surface, so they release body-building material quickly but also turn bitter quickly and can muddy clarity 5:32.
- They extract almost at once. Sifted fines steeped in boiling water held roughly the same TDS from 30 seconds to 10 minutes 13:35.
- More fines at the same nominal grind raises extraction and muddiness 14:22. Fines-heavy burrs lower the point at which a cup turns bitter and flatten complexity 12:37.
- He likens them to seasoning, where a little adds sweetness and balance and too much overwhelms 12:45.
Where they go
- In espresso, fines migrate to the bottom of the puck early and come out first 10:39. Grinding too fine can push microfines and cell-wall fibre through the basket, giving a muddy, astringent shot and inconsistent back-to-back extractions 10:15.
- In pour-over, every pour lifts and drops the bed. Larger particles settle on top and fines sink to the paper. Fewer pours and gentler agitation let less sediment through 10:42. Fines also slow drawdown dramatically 28:06.
What makes more of them
- Espresso grinding makes more fines than filter grinding, and filter burrs are designed to make fewer 4:31. Espresso-geometry burrs deliberately create extra fines to build puck resistance 16:15 16:25.
- Darker roasts are more brittle and make more fines 2:31 3:08. At the same setting a dark roast's peak can sit roughly 100 µm finer than a light roast's 22:28. Dark roasts shatter into fines on almost any grinder, which is why expensive grinders add little for dark espresso 20:50, while light roasts let burr geometry control the result much more 23:24.
- Decaf, Ethiopian coffees and Ethiopian-heavy blends produce more fines and drain slower 39:38 35:32 15:50.
- Long dwell time in the burr chamber, for example behind a clogged chute, regrinds particles into more fines 11:13.
Removing them (a view that changed)
- In 2021 he described how his 2020 US Brewers Cup routine stirred the slurry so fines washed through a mesh into a paper filter that he then swapped out, removing about 75 to 80% of sub-200 µm material mid-brew to get body first and clarity after 1:00 4:01 7:36.
- In December 2024, after about ten hours of paired blind tastings, he concluded sifting gives cheap grinders a small lift and nothing more. Removing all fines makes cups hollow, especially on unimodal grinders 15:50 12:15. He now thinks the competition benefit came from clearing bed blockages for a more even final pour, not from removing bitterness 14:48.
- Sieve catch cups shaken after grinding strip some dust from filter grounds 45:09 13:27. Taking fines out always lowered his measured extraction, so he ground finer to compensate 16:22.
Boulders
- Low-quality grinders produce both many boulders and many fines. Extra pours help extract boulders but keep flushing fines into the paper 10:11.
- Boulders the size of about a third of a bean barely extract and add little resistance, so they act like a smaller effective dose. Matching two grinders by peak particle size gave identical drawdowns even though the cheap grinder's bed looked coarser 11:51 4:38.
- A bigger boulder tail coincided with hollow, under-ripe-tasting cups in his 2026 hand-grinder test 18:29. Yet higher-clarity burrs often show a larger boulder peak, so the chart alone doesn't predict taste 21:21.
- Misaligned burrs make both more fines and more boulders 2:02 (see alignment). Grinding twice (very coarse, then to size) reduced boulders in competition use 0:30.
- The Ditting 807 shows the opposite trade: more fines but a narrow boulder range gives sweetness and body with a wide forgiving window 9:56.
Unimodal, bimodal and the dial-in window
- Definitions. A bimodal grind has a bigger fines hump plus a wider, smaller main peak, typical of crushing more than cutting. A unimodal grind has a small fines hump and a narrow main peak 1:30. No grinder is truly unimodal. The word is shorthand for a narrower peak 10:43, and real grinders are closer to trimodal 8:11.
- Coarser is more unimodal. In his tests, every hand grinder became more unimodal as the grind got coarser, and at about 1000 to 1200 µm they were nearly equal 15:22. So almost any burr does better at filter sizes 34:17.
- Forgiveness against ceiling. A broad distribution gives a wide window of acceptable results but muted nuance. A narrow one is harder to hit and rewards more 23:09 12:38. He puts the broad-distribution ceiling at roughly 60 to 70% of a coffee's potential 6:08 5:43. In a 2025 test, moving many coffees through four grinders at a fixed setting, the wide-peak Niche barely changed shot time while tight-peak aligned flats swung from about 15 to 100 seconds 1:01.
- Style fit. Fines-heavy, bimodal burrs suit thick, traditional espresso but muddy filter 9:30. Ultra-low-fines burrs help fast modern shots less than you might hope and do worse on finer, darker traditional shots, because there are too few fines to build resistance 20:48.
- Clarity without unimodality. Clarity can also come from few fines with a wide peak. A narrow peak plus a moderate fines fraction gives high extraction and clarity but a distinct bitterness 11:11.
How Lance Hedrick's view of PSD changed
- From 2021 to 2022 he leaned on distribution language as a stand-in for flavour, with unimodal burrs giving the most clarity and high-uniformity burrs giving body and sweetness 31:00.
- From 2024 to 2026 he grew increasingly sceptical. Two grinds with the same distribution and extraction can still taste different, since particle shape and heat damage go unmeasured 24:01. PSD doesn't equal flavour, and "more unimodal" doesn't mean cleaner 15:27. His blind tastings showed little correlation with measured unimodality 40:12. He still recommends a more unimodal grind for maximum aroma in light-roast filter, while saying it is not everything 29:48.
Clarity vs body
- Clarity means how distinctly individual flavours separate, unrelated to acidity, sweetness or body 9:38 14:46. He defines juicy as acidity plus mouthfeel that makes you salivate, and body as the whole tactile impression, weight included 9:06.
- The two usually trade off: French press high body and low clarity, V60 the reverse 1:00. Very clear burrs such as SSP multi-purpose give thinner body. Cast and Lab Sweet-style burrs give more body and juiciness 8:09.
- A large unimodal flat can span tea-like clarity to heavy chocolate. Wide-distribution cones cover a narrower range 20:22.
Measuring it
- Sieves are unreliable. Non-spherical grounds slip through holes smaller than their longest side if shaken long enough, and static interferes 2:31 6:09 9:12 8:00.
- Image-based analysers need many samples to be trustworthy. He used 25 readings of 10 g each and matched peaks before comparing 17:28. Matching peak size is a fairer basis for a taste comparison than matching a dial number 16:25.
Heat damage
Heat from fracture, grounds rubbing on grounds, and the motor can drive off volatile aromatics. He finds it most noticeable with very light and delicate coffees 3:07 8:11 4:37. This is one reason he favours slow, even feeding (see slow feeding and RPM).
James Hoffmann's view
- Uneven grinds taste both ways at once. When tiny and large particles mix, the small ones add bitterness and the big ones sourness, both in one cup 4:08 11:20.
- Boulders over fines (a shift in emphasis). In 2020 he said large pieces now worried him as much as fines, because they inevitably under-extract, and that he cared less about fines than before 7:46. By 2024, testing cheap hand grinders, he concluded that at filter settings fewer boulders matters more to taste than fewer fines: a Kingrinder P1 made the most fines yet tasted close to a Comandante, while a Hario Slim with about 14% of grounds over 1500 µm tasted thin 11:45 10:45. This lines up with Lance Hedrick's boulder findings above.
- Fines and surface area. On surface-area charts, fines form their own peak that supplies a large share of the surface. A $50 grinder's fines peak was far bigger than a good grinder's 6:39 23:37.
- Matching numbers is not matching taste. Grinders with quite different distributions can reach similar extraction 9:20. Brews of the same strength can taste different 12:23. And a target micron figure (such as 600 µm) is not useful because matching a peak does not match total surface area 4:05.
- Treat PSD charts as snapshots. He repeatedly warns that a chart only captures one coffee, one setting and one day, so it is no final judgement on a grinder, and that tasting can overturn what the chart suggests 3:33 11:45 16:27 22:03.
- Removing fines. He opposes built-in sieves because they waste coffee 15:54. For a blade grinder he suggests pulsing and shaking, sieving and regrinding the boulders, and rubbing the grounds on paper towel to strip fines 1:02 2:02 3:34.
- Fines in espresso. A paper filter under the puck appears to stop fines blocking the basket holes, so you can grind finer or flow faster 3:08 11:39. Pre-infusion may help by trapping fines in the swollen puck 9:05. Vibration distribution seems to send fines to the bottom and slow the shot 9:08.
- Better grinders allow higher extraction. A more uniform grind tastes good at extractions (about 21.5 to 22%) where a weaker grinder would not, and makes larger doses easier to extract 2:36 3:04.
Daddy Got Coffee's view
Justin (Daddy Got Coffee) frames the grinder as the most important purchase after good coffee because uniformity drives taste: dusty fines over-extract into bitterness while large shards only give up sour compounds, giving a muddled bitter-and-sour cup 2:33 3:03 3:35.
- Fines by method. More fines help espresso (denser puck, more body, more blended flavour) but muddy filter and can stall it 4:08 4:38 3:06 4:05. A fines-heavy espresso grinder will not give crisp pour-over just by going coarser 6:43.
- Regrinding. When grounds pile up against spinning burrs they get reground and uniformity falls. Pre-breakers and controlled feed avoid that 9:16 10:50 15:23.
- Distribution is not the whole story. Particle shape matters too 1:31 13:25. The Kinu Pour Over burr makes plenty of fines and boulders yet brews very clear cups, so the old idea that uniformity is the only route to great pour-over is incomplete 7:13.
- Clarity isn't always better. High-clarity grinders spotlight flaws in coffee and roast and pull back sweetness and body 6:43 17:31 13:25. He keeps a rounded grinder alongside a clarity one 18:33.
- Shaking grounds in a lidded cup homogenises fines and boulders. It made shots notably more consistent on a wide-distribution conical but little difference on a high-uniformity flat 8:46 19:48.
Kyle Rowsell's view
- Sifting roughly 20 g through 300 and 600 µm Kruve screens gave the Niche Zero far more fines than a Sette 270 (2.2 g against about 0.1 g) but fewer boulders 10:29. A Sette 30 and a Breville sifted identically, yet the Breville's grounds were jagged and flat whereas the Sette's were rounded, so round-hole sieves can hide real differences 10:30. That supports Hedrick's later view that a distribution chart does not tell the whole story.
- The Baratza Encore makes more boulders than most, which he thinks explains its above-average acidity 14:17. A cheap Cuisinart's mix of boulders and fines showed up as astringency and mud 2:35.
- A narrow distribution brings clarity and a linear taste, a broad one gives texture, complexity and sweetness 4:36. Unimodal MP burrs trade espresso texture for clarity 5:38 and are less forgiving day to day than brew burrs 4:04. Turbo shots benefit from high-uniformity burrs but work on any grinder 8:22, and a fines-heavy burr limits how fine a turbo can go before flow and extraction drop 8:12.
The Coffee Chronicler's view
- More uniform isn't always tastier. A tighter sieve result sometimes means a worse cup 21:03, and the very uniform Eureka Filtro wasn't exciting 10:18. Particle shape and the mix of sizes matter, and he treats makers' distribution graphs as mostly marketing 10:49 13:58. A particle analyser barely separated SSP MP and Brew burrs on fines even though they taste different 6:39. This agrees with Hedrick's and Daddy Got Coffee's scepticism about charts.
- Sieving shows a big gap between the best flats and conicals but small gaps between good conicals 17:28. A C40, a 1Zpresso JX and a stock DF64 sieved similarly, while a Wilfa Uniform with SSP brew burrs stood out with fewer fines 6:43. Even so, a C40 and a K-Max matched electric flats on clarity in the cup 32:54.
- SSP Brew burrs were so unimodal that espresso was hard to dial, and the MP version added fines to give espresso a normal range 3:06, as Daddy Got Coffee also describes.
- In practice, entry-level grinders such as an Encore or a Hario hand mill make dust, so long ratios turn bitter. Grind a touch coarser at about 1:15 2:30 2:05. Dense light roasts and Ethiopian naturals produce more fines and can stall flat-bottom drippers 5:07 12:16. Chutes and impellers that bounce grounds back into the burrs add heat and fines and cloud pour-over 17:07. Heptagonal vs pentagonal 1Zpresso burrs only differ noticeably with very light roasts brewed around 1:17 to 1:18 3:33.
Sprometheus's view
- Fewer fines mean more even flow, higher extraction and more clarity and acidity 4:33 4:11. On a Lagom Mini at the same setting, Moonshine burrs ran espresso roughly twice as fast as Obsidian, a hint that Obsidian produces more fines 4:02, which matches Brian Quan.
- Unimodal filter burrs keep fines low for clarity but cannot grind fine enough for a classic 9-bar shot without over-extracting. Bimodal sets work for everything 3:16 7:42 3:04 9:11. SSP high-uniformity burrs, by contrast, made extra fines in filter, so brews ran fast and then stalled 4:34.
- Analyser readings. DF54 and DF64 espresso grinds at matched medians were near identical (about 61% vs 62% in the fine band) 4:44. Lagom 01 and P64 medians were 289 and 291 µm, the P64 with SSP MP burrs slightly tighter 6:29. The Femobook A68 was tighter than the Niche Zero's 63 mm Mazzer cone 5:16. Blind burrs put about 9% more in range for espresso and 7% for filter 4:16.
- Screening out fines below 200 µm trades complexity and extraction for clarity 1:02. Layering fines and boulders separately in the basket did not extract smoothly 1:00. Unsifted fines caused a slow start and channelling 6:34.
- His 2020 sift found more clumping and a wider spread from the flat-burr grinder than from the conical 5:04, a counter-example to the generalisation that Lance Hedrick also flags.
European Coffee Trip's view
- Talking with Q-grader Tomo Laca, Brian Quan heard that cheap hand grinders make boulders plus fines whose sharp acidity and bitterness mask flavour, while better grinders give clean, identifiable notes 5:37, as James Hoffmann says of cheap grinders.
- Static in the Comandante's polymer jar holds fines and chaff at the bottom, so less reaches the cup 12:21.
- A plastic mesh in the Hario W60 lets fines and oils through for fuller but muddier body. Paper under the mesh clogged and stalled 5:41.
Brian Quan's view
- Denis Basaric of Kafatek explains that burr surface finish works like sandpaper, so a rougher burr makes more fines and a polished one fewer, and burr spacing is another control 2:00. A 9-bar shot relies on some fines for resistance 3:02. Conicals show two humps in their distribution, which Denis imitated in a flat burr for darker roasts 9:43. A full dose grinds differently from single beans, so a flat pre-breaking burr evens out what reaches the final burr 3:32. Coffee that lingers longer in a conical ends up with more fines 3:06.
- Profiling cannot fully rescue a limited grinder. The hardware caps what is possible 4:36.
- For managing fines in pour-over, a Melodrip lifts fines to the top and walls, which allows a finer grind and longer ratios 15:36. With a fines-heavy grinder, slow the brew and let the bed filter 16:05. Nonwoven filters pass more fines, giving a heavier, murkier cup 25:14.
- SSP's 64 mm Unimodal v1 tastes clearer than today's MP but is tougher to dial, and its lingering mouthfeel makes mistakes easier to notice 6:39 15:24.
For Notchbook
These ideas explain why a pinned setting rarely transfers between grinders, and why the same coffee can need a big change on a tight-peak flat but almost none on a wide-peak conical. See dialling in by grinder type.
Summarised in our own words from the creators' videos, with every point linked to the moment it comes from. Notchbook isn't affiliated with or endorsed by any of these creators, so please watch the originals for full context. Sources
Keep reading
- Burr alignment
- Astringency
- Conical vs flat, and burr geometry
- Grind size and extraction
- Retention, static and RDT
- Seasoning new burrs
- Slow feeding and RPM
- Zero point and grinder scales
- Grinder workflow: single dosing, WDT, RDT, purging and storing beans
- Troubleshooting: what to change when a cup tastes wrong
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