The Fundamentals
Grind size determines how much surface area is exposed to water. Smaller particles mean more surface area, which means faster extraction.
This is the first variable you should adjust when troubleshooting. If your coffee tastes sour, grind finer. If it tastes bitter, grind coarser. This simple rule solves most brewing problems.
Rule of Thumb
Grind adjustment is the fastest way to fix extraction problems. Temperature, ratio, and technique are secondary adjustments.
Surface Area and Extraction
When you grind coffee, you break beans into smaller pieces, creating more surface area for water to contact. The relationship is exponential: halving particle size more than doubles surface area.
Grind Size Reference:
Extra Coarse (cold brew, cowboy coffee)
Chunky, visible fragments. Looks like coarse sea salt or breadcrumbs.
Coarse (French press, cupping)
Distinct particles, like raw sugar or kosher salt.
Medium-Coarse (Clever Dripper, some Chemex)
Slightly finer than coarse, like rough sand.
Medium (V60, Kalita Wave, Chemex)
Standard pour-over grind. Like table salt or fine sand.
Medium-Fine (AeroPress, Moka pot)
Finer than pour-over but not espresso. Like fine sand or table salt.
Fine (espresso, Turkish)
Very fine powder, like flour or powdered sugar.
For pour-over, you're typically working in the medium to medium-coarse range. Small adjustments—one or two clicks on your grinder—can dramatically change extraction.
Impact on Flow Rate
Grind size doesn't just affect extraction—it also controls how fast water moves through the coffee bed. Finer grinds create more resistance, slowing flow and extending contact time.
Too Coarse
Brew time: <2:00
Water rushes through the bed. Low resistance means short contact time. Result: underextraction, sour and thin flavors.
Too Fine
Brew time: >5:00
Water barely trickles. High resistance means prolonged contact. Result: overextraction, bitter and astringent flavors.
Brew time is feedback. If your V60 drains in 90 seconds, grind finer. If it takes 6 minutes, grind coarser. Aim for 2:30-3:30 as a starting point.
Grind Distribution (Fines and Boulders)
No grinder produces perfectly uniform particles. Every grind contains a distribution of sizes:
- •Fines: Tiny particles (dust) that extract very quickly and clog flow
- •Target particles: The grind size you intended
- •Boulders: Large chunks that extract slowly
Better grinders (like burr grinders) produce narrower distributions—fewer fines and boulders, more consistency. Blade grinders produce chaotic distributions with extreme variation.
Grinder Quality Matters
A $50 hand grinder will outperform a $30 blade grinder. A $200 electric burr grinder will outperform both. Grinder quality is the single best equipment upgrade for better coffee.
Making Adjustments
Adjusting grind size is iterative. Start with a baseline, taste the result, and refine.
Adjustment Protocol:
- 1.Start medium: If using a new coffee or grinder, start at medium grind (table salt texture).
- 2.Brew and taste: Note flavor (sour/bitter/balanced) and brew time.
- 3.Adjust incrementally: Change 1-2 clicks (or ~5% on a stepless grinder). Don't make huge jumps.
- 4.Repeat: Dial in over 2-4 brews until you hit the sweet spot.
Important: Change only one variable at a time. If you adjust grind AND temperature simultaneously, you won't know which change caused the improvement (or decline).
Once dialed in, a coffee will remain consistent for several days. As beans age (degas), you may need to grind slightly finer to compensate for reduced CO₂ and slower extraction.