Onions not browning

Why it takes so long

An onion is around 90% water. Before any browning can happen, most of that water has to evaporate — and while there is free water present, the pan surface cannot rise above 100°C, which is well below the temperature at which browning reactions get going.

So the first twenty minutes are pure evaporation. The onions go translucent, then soft, then start to collapse and stick. Only then does colour begin, and it develops slowly at first and faster towards the end.

Turning the heat up does not skip this stage. It burns the onions at the edges while the middle is still releasing water, which is exactly the unpleasant result of trying to caramelise onions in ten minutes.

Sweated, softened, caramelised

Sweated

5–10 minutes, low heat, often covered. Translucent, soft, no colour. The base for most soups and sauces.

Softened and lightly golden

15–20 minutes. Some colour at the edges. Where most recipes actually want you to be.

Properly caramelised

40–60 minutes. Deep brown, jammy, collapsed, sweet. For onion soup, onion jam, burgers.

Burnt

Bitter and acrid at the edges while pale in the middle. The result of high heat and impatience.

How to do it

1. Slice the onions evenly. Uneven pieces brown at different rates and the thin ones burn.
2. Use a wide, heavy pan so there is surface area for evaporation, and do not fill it more than a couple of layers deep.
3. Start on a medium heat with a generous amount of butter or oil and a good pinch of salt. Salt draws water out and speeds the first stage.
4. Cover for the first ten minutes to soften them, then take the lid off so the water can evaporate.
5. Turn the heat down to medium-low and stir every few minutes, scraping the base.
6. When brown deposits build up on the pan, add a splash of water and scrape them into the onions. This is where a great deal of the flavour is, and repeating it several times deepens the colour considerably.
7. Keep going until they are deep brown and jammy. Then keep going a little longer.

Honest shortcuts

• A pinch of bicarbonate of soda raises the pH and speeds browning reactions substantially. Use a very small amount — too much gives a soapy taste and a mushy texture.
• A little sugar helps colour, though it caramelises rather than browning the onion itself, so the flavour is sweeter and less complex.
• Deglazing repeatedly with water is the best genuine accelerator, and it costs nothing.
• Starting with a higher heat for the first ten minutes, then dropping it, saves a little time on evaporation.
• Make a large batch and freeze it. Caramelised onions freeze perfectly in ice-cube trays, and this is the real answer.

Common questions