Grind Size: The One Thing Most Home Setups Get Wrong

If a brew is disappointing, look at the grinder before you look at the beans. Grind size sets how much surface area the water has to work on, and surface area sets the speed of extraction. Nothing else in a home setup moves the cup as far. Same coffee, same recipe, two grind settings, and you can go from thin and sour to sweet and full.

Extraction runs in an order. Water takes out acids and salts first, then sugars and the compounds that read as sweetness and body, then the dry, bitter ones. Grind decides how far down that list you travel in the time your brewer allows. Stop early and the cup is sour and thin. Go too far and it turns bitter and drying.

A grind scale you can actually see

Grinder numbers mean nothing between machines. Compare against what is already in the kitchen.

• Espresso, fine. Between flour and caster sugar, and it clumps when pinched. A common shot is 18g in, 36g out (1:2) in 25 to 30 seconds, water 92 to 95C.
• Moka pot and AeroPress, fine to medium-fine. Caster sugar, just gritty between the fingers.
• Pour-over, medium. Table salt. Around 60g of coffee per litre of water, water 92 to 96C, 2:30 to 3:30 total for a 250g brew. Chemex sits a touch coarser.
• Cafetière, coarse. Coarse sea salt or rough breadcrumbs. Same 60g per litre, four minutes steeping, then break the crust, skim, and plunge slowly.
• Cold brew, coarser still. Closer to demerara, 12 to 16 hours in the fridge.

Bean, roast level and your local water will all shift them.

What a blade grinder is doing to your coffee

A blade grinder is a propeller in a chamber. It does not grind to a size, it smashes coffee until you let go of the button. What comes out is dust and boulders in the same batch, with very little in between.

The dust over-extracts in seconds. The boulders give up almost nothing. So the cup is over-extracted and under-extracted at once: bitter and sour together, muddy in the body, hollow where the sweetness should sit. That is the genuinely confusing part, because bitterness normally tells you to grind coarser and sourness tells you to grind finer, and you cannot do both. No change of recipe corrects two opposite errors at the same time. In a cafetière the fines also slip through the mesh and carry on extracting in the cup, which is why the last mouthful is harsher than the first.

Burrs, and why consistency beats price

A burr grinder crushes beans between two surfaces with a set gap, so particles only escape once they are small enough to pass through. The spread is far tighter: fewer fines, fewer boulders, and a brew you can steer. What you are buying is consistency, not power. A modest hand grinder with steel burrs will out-brew a much more expensive blade device every time. Flat against conical burrs matters far less at home than equipment forums suggest. Clean burrs matter more, because old oils go stale in there and taint everything ground after them.

Why grinding fresh is not fussiness

Most of a bean's surface area is inside it, sealed in and pressurised with carbon dioxide from roasting. Grinding opens all of it at once, and the aromatics start leaving immediately. Ground coffee is noticeably flat within half an hour and largely spent within a day or two. Whole beans hold for weeks.

It is also why a roast date is worth more than a best-before date, and every Dāku bag carries one. As a rough guide, filter tends to be at its best around four to ten days off roast and espresso a little later, seven to fourteen days, once some of that gas has gone. Store beans sealed and opaque at room temperature, not in the fridge, where they pick up moisture and smells.

Adjust by taste, not by numbers

Brew it, taste it, then act on what you tasted.

1. Sour, thin, salty, finishing too soon: grind finer.
2. Bitter, drying, harsh: grind coarser.
3. Hold dose, water and ratio fixed while you move the grind. One variable at a time.
4. Move in steps you can taste. On espresso that means one step at a time, because the window is narrow; on filter you can afford two or three.
5. On espresso, keep dose and output fixed and watch the clock. A fast shot wants finer, a choked one wants coarser.
6. Note down what worked. Every new bag needs a different setting.

One practical note

We sell whole beans rather than ground, because grind belongs with the person holding the brewer. If you want to know what happens before that point, how we roast covers the computer-controlled, clean-energy setup at our three roasting sites — Kensington and Monument in London, and Gurney in Penang — in batches from 100g to 4kg. The other four Dāku shops are supplied from the London roasteries.