Brewing coffee has a reputation for complexity it does not deserve. There are three variables that matter, they interact in predictable ways, and once you know which direction each one pushes you can fix almost any bad cup on the next attempt.
Extraction, in one paragraph
Brewing is dissolving. Water pulls compounds out of ground coffee in a rough order: acids and fruit character first, then sugars and the substances that give body, then the bitter and astringent compounds last. Stop too early and you get under-extraction — sour, thin, hollow. Go too far and you get over-extraction — bitter, drying, dull. Everything below is about landing between the two.
Dial one: grind size
Grind controls surface area, and surface area controls how fast water can extract. Finer grounds extract faster; coarser grounds extract slower. This is the most powerful dial you have, and the one to reach for first.
Grind consistency matters as much as grind size. A grinder that produces both dust and boulders over-extracts the dust and under-extracts the boulders in the same brew, which tastes bitter and sour at once and cannot be fixed by adjusting anything else.
Dial two: ratio
Coffee to water, by weight. For filter coffee, somewhere between 1:15 and 1:17 is the usual working band — about 60 grams of coffee per litre of water. Ratio mostly controls strength rather than extraction: a weak brew and an under-extracted brew are different problems with different fixes.
Weigh both sides if you can. Scoops vary by roast level, bean size and how hard you pack them, which is why the same scoop gives a different drink from a light roast and a dark one.
Dial three: water
Brew between about 90 and 96 °C. Water off a rolling boil drops into that band in roughly thirty seconds in an open kettle. Hotter extracts faster — useful for a light roast, risky for a dark one, which is already fragile and bitters easily.
The water itself is the variable people forget. Very soft water gives thin, flat coffee because there is nothing in it to carry flavour; very hard water mutes acidity and scales equipment. Filtered tap water is usually a better brewing water than distilled.
Starting points by method
Treat these as a first attempt to adjust from, not as the correct answer.
French press
Coarse grind. 1:15 — try 30 g to 450 ml. Water 93 to 96 °C. Steep four minutes, stir the crust in gently at the end, press slowly, and decant immediately. Coffee left sitting on the grounds in the press keeps extracting and turns bitter.
Pour-over, cone or V60
Medium-fine grind. 1:16 — try 20 g to 320 ml. Water 92 to 94 °C. Wet the bed with about twice the coffee’s weight in water and wait 30 to 40 seconds for the bloom, then pour in stages. A total brew time of two and a half to three and a half minutes is a healthy range: much faster means grind finer, much slower means grind coarser.
Drip machine
Medium grind. 60 g per litre. The machine chooses the temperature, so grind is your only real dial. Rinse the paper filter before brewing and never leave the jug on a hotplate — twenty minutes on a warming plate does more damage than any grind error.
Stovetop moka pot
Fine, but not as fine as espresso. Fill the basket level and do not tamp. Start with hot water in the base so the coffee is not sitting over a slowly heating chamber. Take it off the heat as soon as the stream turns pale and begins to sputter — everything after that point is bitter.
Espresso
Fine grind. Aim for roughly double the dose in liquid weight — about 18 g in, 36 g out — in 25 to 32 seconds, at 92 to 94 °C. If the shot runs too fast, grind finer; too slow, grind coarser. Adjust the grind, not the time.
Boiled and spiced coffee
The traditional preparation — coffee boiled in a pot, often with ginger or cardamom — is not a precision exercise and does not need to be. Grind medium, keep the boil short, and let it settle before pouring. Roast choice matters far more than grind here: a Medium-Dark or Dark profile keeps its character against both the boil and the spice, where a light roast is simply lost.
How to fix a cup that came out wrong
- Sour, thin, or it finishes abruptly — under-extracted. Grind finer, raise the water temperature, or extend the brew time. Change one.
- Bitter, drying, or dull and heavy — over-extracted. Grind coarser, lower the temperature, or shorten the brew.
- Watery but still harsh — the ratio is too low and the grind too fine. Use more coffee and grind coarser.
- Strong but unpleasant — the ratio is high and extraction is off. Fix extraction first with the grind, then adjust strength with the ratio.
- Bitter and sour at the same time — usually the grinder, not the recipe.
Matching the grind to the roast
Roast level changes bean density and solubility, so the same brewer wants slightly different settings for different profiles. Lighter roasts are denser and less soluble and generally need a finer grind, hotter water or a little more time. Darker roasts are more soluble and more fragile: grind a touch coarser and drop the temperature, or they turn bitter quickly.
All four Rocky profiles are described on Our Coffee, and choosing your roast covers which one suits the way you drink coffee.
Questions we get asked
What grind should I ask for when I order?
Whole bean if you own a grinder, because ground coffee stales within days. If you do not, tell the team which brewer you use — French press, pour-over, drip machine, stovetop pot or espresso — and the grind can be matched to it.
Why does my coffee taste sour?
Sourness almost always means under-extraction: the water did not dissolve enough from the grounds. Grind finer, use water closer to 94 °C, or extend the brew time, changing only one of the three at a time.
Does the water I use really matter?
Yes. Very soft water produces thin, flat coffee because it carries little flavour, and very hard water mutes acidity and scales equipment. Filtered tap water is usually better for brewing than distilled or heavily softened water.
