Ingredient

Egg

An egg is the most versatile thing in a kitchen because it does at least five different jobs — it sets, it thickens, it emulsifies, it aerates and it browns. All five come from protein, and all five are controlled by exactly one variable: temperature.

White and yolk set at different temperatures

Egg proteins are folded up in a compact shape. Heat unfolds them, they tangle with each other, and the liquid turns solid. That is setting, and once it has happened it cannot be undone.

The white and the yolk do it at different points. The white begins to firm noticeably below the yolk, and thickens further as it goes; the yolk stays fluid longer, then thickens, then goes crumbly. That gap is the whole of egg cookery. A soft-boiled egg is a set white and a liquid yolk. A custard is caught in the middle of the yolk's range. A hard-boiled egg is both fully set — and cooked further, it goes rubbery and the yolk develops a grey-green ring where sulphur from the white meets iron from the yolk.

Everything on this page follows from the fact that gentle heat gives you the range and fierce heat skips past it.

The five jobs an egg does

Setting

The obvious one. Fried, boiled, poached, baked, and the structure of a quiche or a frittata.

Thickening

Yolk proteins partially set and hold liquid, giving a custard, a crème anglaise or a carbonara sauce its body without any flour.

Emulsifying

The yolk contains lecithin, which lets oil and water hold together. This is mayonnaise, hollandaise and aioli.

Aerating

Whipped white traps enormous quantities of air. Meringue, soufflé, mousse and much of the lift in a sponge.

Browning and glazing

Egg proteins and sugars brown readily, so a wash of beaten egg gives pastry its colour and shine.

The habits that make eggs work

• Low and slow, almost always. Scrambled eggs, custards and curds all fail in the same direction — too hot, too fast — and none of them can be un-failed.
• Temper anything hot going into eggs. Pour a little of the hot liquid into the beaten eggs while whisking, then return the mixture. Hot liquid poured onto cold eggs scrambles them instantly.
• Room-temperature eggs whip further and emulsify more readily. Cold ones from the fridge come out of a shell more cleanly and separate more reliably.
• Not a speck of yolk in whipped whites. Fat prevents the foam forming, and yolk is fat. Separate over a third bowl so one bad egg does not spoil the lot.
• A clean, grease-free bowl for whites. Metal or glass, not plastic, which holds a film of fat however well washed.
• Older eggs peel more easily after boiling; fresher eggs poach more neatly. The white of a fresh egg holds together; the shell of an older one has separated slightly from the membrane.

Scrambled eggs that are not rubbery

The single most common egg failure, and the fix is entirely about heat.

1. Beat the eggs properly, with a pinch of salt. Salt a few minutes in advance if you can — it loosens the proteins slightly and gives a softer set.
2. Use a non-stick pan over low heat, with butter.
3. Stir constantly and gently with a spatula, pulling from the edges into the middle. You are making small curds, not an omelette.
4. Take the pan off the heat while the eggs still look slightly underdone and wet. They keep cooking in the residual heat of the pan for a good while.
5. A spoonful of cream, crème fraîche or cold butter stirred in at the end stops the cooking and enriches them.

Safety, and what this page does not say

FoodHQ does not publish cooking temperatures or keeping times for raw meat, poultry, fish or eggs. Those are safety guidance and need qualified review this site does not have. In the UK the Food Standards Agency publishes them. Their guidance covers raw and lightly cooked eggs, who should be careful with them, and how eggs should be stored.

What is worth saying as a cook: buy eggs from a source you trust, keep them somewhere consistently cool, and if one smells at all sour or sulphurous when cracked, throw it away without arguing with it. Crack each egg into a separate cup before adding it to a bowl of others, which costs nothing and occasionally saves a recipe.

Common questions