Sweating

Why you would deliberately avoid browning

Browning creates a large number of new, assertive flavour compounds. Sometimes that is exactly what a dish wants — a French onion soup, a ragù, a curry base. Sometimes it is not.

A delicate fish soup, a pale velouté, a leek and potato soup or a risotto base wants the sweetness and body that onions give without the toasted, caramel notes that would dominate. Sweating gets the first without the second.

It also cooks the vegetables through evenly. Browned onions are often soft at the edges and firm in the middle; sweated onions are soft throughout, which matters when they are going to be blended.

How to do it

1. Cut the vegetables evenly and reasonably small. Sweating relies on gentle heat, so large pieces take a long time.
2. Use a heavy pan with a lid and a modest amount of butter or oil — enough to coat, not to fry.
3. Set the heat low. Low enough that nothing sizzles aggressively.
4. Add a pinch of salt at the start. Salt draws water out of the vegetables, and that water is what stops them browning.
5. Cover the pan, or cover it with a disc of greaseproof paper pressed onto the surface — a cartouche — which traps moisture while letting a little steam escape.
6. Cook for ten to twenty minutes, stirring occasionally, until translucent and completely soft.
7. If anything starts to colour, turn the heat down and add a splash of water.

Sweating against its neighbours

Sweating

Low heat, some fat, lid on, salt early. Soft and translucent, no colour. Ten to twenty minutes.

Sautéing

Higher heat, some fat, no lid, moved frequently. Light colour, still some bite. A few minutes.

Caramelising onions

Low to medium heat, no lid, forty-five minutes or more. Deep brown, jammy and sweet.

Frying

High heat, more fat, browning intended and fast.

The salt

Early in sweating, to draw water out. Late in browning, so the water leaves before the salt arrives.

Where it belongs

• A soffritto or mirepoix at the start of a soup, stew or sauce, where a clean sweet base is wanted.
• Risotto, where browned onion would show through the finished dish.
• Leek and potato soup and other pale soups, where colour would spoil the look as well as the flavour.
• Fish soups and sauces, which want no toasted notes at all.
• Béchamel and velouté bases.
• Fillings — for quiches, tarts and pies — where the vegetables need to be soft and not assertive.
• Not for a ragù or a curry, both of which want the browning.

Common questions