Coffee Grinding 101: Why Grind Size Matters

If there's one variable that separates truly excellent home coffee from merely acceptable coffee, it's the grind. You can have the finest single-origin beans, the most expensive espresso machine, and water filtered to perfection, but if your grind is wrong, your coffee will disappoint. Understanding grind size and how it affects extraction is fundamental knowledge for any home barista. In this guide, we'll demystify the science behind grinding and give you the practical skills to dial in any brewing method.

The Science of Extraction

Coffee brewing is, at its heart, a process of extraction. Hot water acts as a solvent, dissolving the soluble compounds in roasted coffee and carrying them into your cup. These compounds include acids that provide brightness, sugars that contribute sweetness, and various aromatics that create coffee's complex flavour profile. But extraction is not all good—over-extract, and you pull out bitter, astringent compounds that overwhelm the pleasant flavours.

Grind size directly controls extraction rate. When you grind coffee, you're increasing its surface area. Finer grinds have dramatically more surface area than coarse grinds, meaning water can extract soluble compounds much faster. A powder-fine grind exposes so much surface area that extraction happens almost instantly, while a very coarse grind requires extended contact time to extract adequately.

Grind Size and Brewing Method

Different brewing methods require different grind sizes because they have different contact times and extraction mechanisms. Here's a general guide:

Espresso (Very Fine)

Espresso extraction happens in just 25-30 seconds under nine bars of pressure. To achieve proper extraction in this brief window, espresso requires an extremely fine grind—almost powdery. The pressurised water forces through the tightly packed coffee bed, extracting concentrated flavour. If your grind is too coarse, water rushes through too quickly, producing a thin, sour shot. Too fine, and water can barely pass through, resulting in bitter, over-extracted espresso or a "choked" machine.

Moka Pot (Fine)

The moka pot sits between espresso and filter coffee in terms of pressure and contact time. A fine grind—slightly coarser than espresso—works best. Too fine and the pot can struggle to push water through, potentially causing safety concerns with older models. Too coarse and the resulting coffee will be weak and watery.

AeroPress (Medium-Fine to Medium)

The AeroPress is famously versatile, and grind size is one variable you can experiment with. For standard recipes with one to two minutes of steeping, a medium-fine grind works well. For faster, more concentrated brews, go finer. For longer immersion times, coarsen up. The beauty of AeroPress is its forgiveness—the paper filter and manual pressing let you correct for less-than-perfect grind choices.

Pour Over (Medium to Medium-Fine)

Pour over methods like the V60 or Chemex rely on gravity to pull water through the coffee bed. The grind must be fine enough to provide resistance that slows water flow, but coarse enough that water doesn't pool and stall. Target a medium to medium-fine grind, adjusting based on your total brew time. If water drains too quickly (under 2.5 minutes for a single cup), grind finer. If it takes longer than four minutes, coarsen up.

Drip Coffee Maker (Medium)

Automatic drip machines typically work best with a medium grind—something resembling coarse sand or raw sugar. The machine controls water flow, so you have less adjustment available, but getting the grind right ensures the four to six minute brew time extracts properly without over-extraction.

French Press (Coarse)

French press is a full immersion method with a metal mesh filter, requiring a coarse grind to prevent excessive fine particles in your cup and to avoid over-extraction during the four-minute steep. Think breadcrumb-sized particles. If your French press coffee tastes bitter or muddy, your grind is likely too fine.

Cold Brew (Extra Coarse)

Cold water extracts much more slowly than hot water, so cold brew requires extremely long contact times (12-24 hours) and very coarse grinds to prevent over-extraction. The grind should resemble rough sea salt or even peppercorns.

Burr Grinders vs. Blade Grinders

Not all grinders are created equal, and this matters immensely for grind consistency. Blade grinders—the cheap option you find in supermarkets—use spinning blades to chop beans. The result is wildly inconsistent particle sizes: some powder, some chunks, and everything in between. These different-sized particles extract at different rates, making it impossible to achieve balanced flavour.

Burr grinders crush beans between two abrasive surfaces (burrs), producing much more uniform particles. Conical burrs use a cone-shaped inner burr rotating inside a ring-shaped outer burr. Flat burrs are two parallel disc-shaped burrs. Both produce far superior results to blade grinders. For espresso, a quality burr grinder isn't optional—it's essential. For other brewing methods, a burr grinder still makes a noticeable difference in cup quality.

How to Dial In Your Grinder

Dialling in means adjusting your grind size until you achieve optimal extraction. For espresso, this is a precise process:

1. Start with a baseline: Use your grinder's recommended setting for espresso or the middle of its espresso range.
2. Dose consistently: Use the same amount of coffee (typically 18-20 grams for a double shot) every time while dialling in.
3. Time your shot: Aim for 25-30 seconds from the moment you start the pump until you stop it.
4. Taste and adjust: If the shot runs too fast (under 20 seconds) and tastes sour, grind finer. If it runs too slow (over 35 seconds) and tastes bitter, grind coarser.
5. Make small adjustments: Change one or two notches at a time. Large jumps make it hard to find the sweet spot.

For filter methods, the process is similar but based on total brew time and taste. If your pour over drains too quickly and tastes thin, grind finer. If it stalls and tastes bitter, grind coarser. Always taste your coffee critically—your palate is the ultimate judge.

Grind Freshness: The Final Variable

Ground coffee goes stale dramatically faster than whole beans. Within minutes of grinding, aromatic compounds begin escaping, and oxidation starts degrading flavour. By the time pre-ground coffee reaches your pantry, it's lost much of what made it special.

Grinding fresh for each brew is the single biggest improvement most home brewers can make. A modest burr grinder producing fresh-ground coffee will outperform pre-ground beans in an expensive machine every time. Even if you can't grind immediately before brewing, grinding daily rather than weekly makes a substantial difference.

Environmental Factors

Grind size isn't a set-and-forget variable. Even with the same beans and grinder, you may need to adjust based on environmental conditions:

• Humidity: High humidity can cause coffee to absorb moisture, requiring a coarser grind. Low humidity may require grinding finer.
• Bean age: As beans age and degas, they require finer grinding to maintain extraction levels.
• Temperature: Both ambient temperature and bean temperature affect grind. Some baristas refrigerate beans specifically for more consistent grinding.

Don't be discouraged if yesterday's perfect setting doesn't work today. Small adjustments are normal and part of the craft of home brewing.

The Path to Better Coffee

Mastering grind size takes practice, but it's deeply rewarding. Start by understanding your brewing method's requirements, invest in the best burr grinder you can afford, and develop the habit of critically tasting your coffee. Over time, you'll develop an intuition for what needs adjusting and why. That intuition, combined with technical knowledge, is what transforms a coffee hobbyist into a true home barista.