Ingredient

Coffee

Coffee is the roasted seed of a fruit, ground and infused in hot water. Almost everything that makes one cup better than another comes down to three decisions — how dark it was roasted, how finely it was ground, and how long the water spent in contact with it.

What roasting does

A green coffee bean tastes of almost nothing. Roasting is what creates coffee flavour, and it does it by browning: the same family of reactions that browns bread crust and seared meat, running inside a bean for somewhere between eight and twenty minutes.

The longer it runs, the more of the bean's original character is consumed and the more of the roast's own character replaces it. So a light roast keeps the acidity and the fruit the bean arrived with and tastes bright, sometimes startlingly so. A dark roast has traded that for the bitter, smoky, chocolatey notes that roasting creates, and tastes more like every other dark roast. Neither is stronger than the other in caffeine terms in any way worth worrying about.

If you dislike a coffee, the roast level is the first thing to change and the cheapest.

Grind size, by method

Grind decides how much surface the water meets, which decides how fast it extracts. Getting it wrong is the commonest reason coffee tastes wrong, and the direction of the error is diagnostic.

Cafetière or French press

Coarse, like coarse sea salt. Four minutes, then plunge. Too fine and it turns muddy and bitter and clogs the plunger.

Filter or pour-over

Medium, like granulated sugar. Two and a half to four minutes depending on the device.

Aeropress

Medium-fine, and forgiving. It tolerates a wider range than anything else.

Moka pot

Fine-medium, but not espresso fine — espresso grind chokes it and scorches the coffee.

Espresso

Very fine, almost powdery, and it needs adjusting for the specific coffee. Around 25 to 30 seconds for a shot.

Cold brew

Very coarse, and twelve to twenty-four hours in cold water. The low temperature is why it tastes so much less acidic.

Sour or bitter — reading the cup

These are the two failure modes and they point in opposite directions, which makes them useful.

• Sour, thin, sharp, disappointing means under-extraction. The water did not get enough out. Grind finer, brew longer, use hotter water, or use more coffee.
• Bitter, harsh, dry, hollow means over-extraction. The water got too much out, including the parts you did not want. Grind coarser, brew shorter, use slightly cooler water.
• Both at once usually means the grind is uneven — a blade grinder producing dust and boulders in the same batch, where the dust over-extracts while the boulders under-extract.
• Flat and stale is not extraction at all. Ground coffee loses its aroma within days; whole beans hold it for weeks.

Coffee as an ingredient

In cooking, coffee is used for bitterness and depth far more often than for its own flavour. Used that way it disappears into the dish and leaves it tasting more of itself.

• Chocolate cake and brownies. A spoonful of strong coffee or espresso powder in the batter makes chocolate taste more like chocolate. You will not taste coffee.
• Chilli, beef stews and braises. Coffee brings the bitter, roasted note that long cooking otherwise has to build from scratch.
• Rubs for beef and pork. Ground coffee with salt, sugar and pepper forms a dark crust and behaves like a spice.
• Tiramisu and coffee custards, where coffee is the flavour rather than the backing.
• Deglazing. A splash of leftover black coffee into a pan of beef fond does much of what red wine does.

Storing it

Coffee's enemies are air, moisture, heat and light, in roughly that order. An airtight, opaque container at room temperature in a cupboard is better than the fridge, where a cold container pulls in condensation every time it is opened and coffee readily takes up the smells around it.

Buy whole beans and grind them as you use them if you can. It is the single change that improves a home cup most, and it costs nothing after the grinder. Freshly roasted coffee also needs a few days to settle — very fresh beans release enough carbon dioxide to disrupt brewing.

Buying and storing it

• Buy whole beans and grind them as you need them. Coffee stales quickly once ground, for the same reason as pepper and spices — the aroma compounds are volatile.
• Look for a roast date rather than a best-before. Coffee is best from a few days to a few weeks after roasting.
• Store it airtight, at room temperature, away from light. Not in the fridge, where it absorbs smells and picks up condensation.
• Grind size matters enormously and is matched to the brewing method: coarse for a cafetière, medium for filter, fine for espresso. A wrong grind is the commonest reason home coffee is bitter or sour.
• Bitter usually means over-extracted — too fine, too long, or water too hot. Sour usually means under-extracted — too coarse, too fast, or water too cool.

Common questions