Input lever
Grind & Particles
Wheel face
Grinder model
The grinder used to prepare the coffee.
Grinder design affects fines, retention, heat, and repeatability even when the nominal setting looks similar.
AeroPress Wheel Domain
Grind & Particles
Domain 03 · 9 controls · 9 states, metrics & outcomes
Grind & Particles covers how whole beans become particles and how that particle system behaves before and during brewing.
Domain 03
9 controls · 9 states, metrics & outcomes
Grind & Particles is one of the ten primary AeroPress Wheel domains and gives brewers a structured way to control grind decisions.
Why It Matters
Particle size distribution affects extraction speed, flow resistance, fines migration, permeability, clogging risk, and brew-to-brew consistency.
Use It To
Treat this as a physical system, not just a click number. Grinder, burrs, RPM, sifting, and fines handling can all change the same nominal grind setting.
How To Read This Domain
Start with the controls in this domain, then read the states, metrics, and outcomes they tend to influence. In practice that keeps brew notes honest: it separates the levers a brewer chose from the signals the brewer observed afterward.
That distinction matters during dial-in because recipe language often collapses cause and effect into one sentence. This domain page is designed to keep them apart so a later cup change can be traced back to a clearer brewing decision instead of a vague impression.
Read the page from top to bottom when you want the broad logic, then use the related variables and linked domains when you need to branch into a narrower troubleshooting path.
Controls
Input lever
Grind & Particles
Wheel face
Burr set
The burr geometry installed in the grinder.
Burrs shape PSD, fines tendency, and flavor presentation, so they belong in the recipe record.
Input lever
Grind & Particles
Advanced detail
Burr alignment
How evenly the burrs are aligned.
Misalignment can widen the particle distribution and make click settings less comparable across setups.
Input lever
Grind & Particles
Wheel face
Grind setting
The selected grind size setting.
It is one of the strongest levers over extraction rate and flow, but it only has meaning alongside the grinder and burr context.
Input lever
Grind & Particles
Wheel face
Grind speed / RPM
The speed at which the grinder is operated.
RPM can change fines, static, heat rise, and therefore the practical PSD of the coffee.
Input lever
Grind & Particles
Wheel face
Sieving
Separating grounds by particle size after grinding.
Sieving can narrow PSD, reduce fines, and change flow or clarity, but only if the removed fraction is defined and tracked.
Input lever
Grind & Particles
Detail panel
Fines removal
Removing very small particles from the grounds.
Removing fines can improve clarity and flow predictability, but it may also reduce body and change extraction behavior.
Input lever
Grind & Particles
Wheel face
Chaff removal
Removing chaff from beans or grounds.
Chaff can contribute dryness, papery notes, or handling inconsistency, especially in competition prep.
Input lever
Grind & Particles
Advanced detail
Reintroduced fines
Adding a removed fines fraction back into the brew deliberately.
Reintroduced fines can change body, extraction, and flow, but only if the amount and timing are controlled carefully.
States, metrics & outcomes
Process state
Grind & Particles
Advanced detail
Median particle size
The middle of the particle size distribution.
It influences baseline extraction speed, but it is only part of the PSD story.
Process state
Grind & Particles
Wheel face
PSD width
How wide the particle size distribution is.
A wider distribution can create more uneven extraction and more variable flow behavior.
Process state
Grind & Particles
Wheel face
Fines share
The proportion of very small particles.
Fines extract quickly, migrate easily, and can sharply change pressure and texture.
Process state
Grind & Particles
Detail panel
Boulder share
The proportion of very large particles.
Too many boulders can reduce total extraction or make the coffee feel simultaneously thin and harsh.
Process state
Grind & Particles
Advanced detail
Ground temp rise
The temperature increase caused by grinding.
Higher grind heat can shift aroma retention and can signal a different grinding condition than intended.
Measured metric
Grind & Particles
Wheel face
Grinder retention / loss
Coffee retained in the grinder or lost during transfer.
It changes the actual dose into the brewer and can silently break mass consistency.
Direct observation
Grind & Particles
Detail panel
Static / clumping
Electrostatic charge and clump formation after grinding.
Static affects transfer loss and clumping affects how evenly the grounds wet in the brewer.
Process state
Grind & Particles
Wheel face
Bed permeability
How easily liquid can move through the grounds.
Permeability strongly affects press resistance, clogging, and the viability of slow-flow recipes.
Process state
Grind & Particles
Detail panel
Uniformity
How even the grounds are as a brewing particle system.
Uniformity shapes the cleanliness and stability of the extraction more than the click setting alone.
Common Mistakes
- Writing only a click number without naming the grinder and burrs.
- Saying a coffee was sifted without saying what was removed.
- Treating grinder retention as if it were the recipe dose itself.
Competition Notes
- Slow-RPM grinding, fines removal, and chaff removal appear most often in advanced competition recipes.
- Reintroduced fines are an experimental technique, not a default recommendation.
Recipe Language
Comandante C40, 24 clicks.
31 clicks, sifted at 200 µm, blow chaff, grind slow RPM.
Domain Context
Grind & Particles is one of the ten primary AeroPress Wheel domains and gives brewers a structured way to control grind decisions.
What To Measure
- Log grinder model, burrs, and setting together.
- Track whether chaff or fines were removed and whether they were reintroduced.
- Note retention/loss when dose precision matters.
Related Domains