Ingredient

Onion

An onion is four different ingredients depending on how long it has been in the pan. Raw it is sharp and hot; softened it is sweet and almost invisible; browned it is savoury; properly caramelised it is jammy and nearly a condiment. Most recipes that disappoint were rushing between two of those.

The four stages

Onions are mostly water, and a good deal of what is left is sugar. Heat drives off the water and concentrates the sugar, and once the water is gone the sugar starts browning. Everything an onion does in a pan follows from that sequence, which is why it cannot be hurried past a certain point.

The mistake almost everyone makes is calling the second stage the fourth. Fifteen minutes of medium heat gives you soft, sweet, pale onions, which is what most dishes actually want. It does not give you the dark, sticky, deeply savoury stuff on a French onion soup, and no recipe that says "caramelise the onions, about 10 minutes" has ever produced it.

How long each stage takes

Sliced onions, medium heat, a good layer of fat, a wide pan. Times are approximate and depend heavily on how crowded the pan is.

Sweating — 5 to 8 minutes

Translucent, floppy, no colour at all. Low heat and a lid. The base of most soups and sauces.

Softened — 10 to 15 minutes

Soft, sweet, edges just turning gold. What most recipes mean when they say "until soft".

Browned — 20 to 30 minutes

Genuinely golden through, noticeably sweeter, volume much reduced. Good in a ragù or a curry base.

Caramelised — 40 to 60 minutes or more

Dark brown, jammy, collapsed to a fraction of the starting volume. Low heat, stirred often, and there is no shortcut.

Getting it right

• Use a wide pan. Onions release a lot of water and a crowded pan steams them instead of browning them.
• Salt early. Salt draws water out, which speeds up the softening stage considerably.
• Deglaze as you go. The brown film that forms on the pan base is where much of the flavour is. A splash of water lifts it back into the onions, and you can do it several times.
• Do not turn the heat up to save time. Onions scorch at the edges long before the middle is done, and scorched onion is bitter.
• Slice with the grain — root to tip — if you want them to hold their shape, and across the grain if you want them to collapse.

Which onion

Brown or yellow

The default. Enough sugar to caramelise well, enough bite to stand up raw in small amounts. Use this unless told otherwise.

Red

Milder and sweeter raw, so the usual choice for salads, salsas and pickling. Loses its colour when cooked and turns a dull grey-purple.

White

Sharper and cleaner, with less of the sulphurous depth. Common in Mexican cooking.

Shallot

Finer, sweeter, more delicate. Worth the extra money in a dressing, a sauce or anything where the onion is the flavour rather than the base.

Spring onion

A different job entirely — a green, fresh note added late or raw, not a base.

Why they make you cry

Cutting an onion breaks cells and lets an enzyme reach a sulphur compound, much as with garlic. The difference is that one of the products is volatile and drifts upwards, and on contact with the water in your eyes it forms an irritant. Your eyes water to flush it out.

What genuinely helps: a sharp knife, which crushes fewer cells than a blunt one; a chilled onion, since cold slows the reaction and reduces how much escapes; and moving air, an extractor fan or an open window, which carries it away before it reaches you. Cutting the root end last helps because the root holds a high concentration. Most of the other advice — bread in the mouth, a candle, holding a spoon — does nothing.

Turning onions into something that keeps

Onions store well raw and better still once cooked down.

• Onion chutney, or onion marmalade. The sweetness is made rather than added — the onions need forty-five minutes to an hour on a low heat before anything else goes in, and rushing that is why home-made versions disappoint.
• Pickled onions, dry-salted overnight before the vinegar. That salting is what keeps them crunchy, and skipping it is why they go limp.
• Caramelised onions frozen in portions, which turns an hour of work into a shortcut for months of cooking.
• Quick-pickled red onion, sliced thin in warm brine, ready in an hour and useful all week on almost anything.
• Onion skins in stock, which add colour and a little sweetness rather than being waste.

Common questions