Shock

To shock is to move food straight from boiling water into a bowl of ice water. The cold stops the cooking at once, so the food does not soften from its own leftover heat. It is the second half of blanching. British recipes often call it refreshing, and they may use cold running water instead of ice.

How to do it

1. Before you start cooking, fill a large bowl with half ice and half cold water. Use about as much ice water as boiling water.
2. Cook the food in boiling water.
3. Lift it out with a spider or slotted spoon, or drain it in a colander, and drop it straight into the ice water.
4. Stir gently so the cold reaches every piece. Add more ice if it melts.
5. Leave it just until cold all the way through, usually as long as it was boiled. Green beans need 2 to 3 minutes.
6. Drain and dry well on a towel.

How to tell it is done

The food feels cold right through, not just on the surface. Bite or cut a thick piece to check the center.

Why it works

Food keeps cooking for a while after it leaves the heat, because the outside is hotter than the middle. Ice water pulls the heat out fast, so vegetables stay crisp-tender and bright green instead of turning olive and soft. For boiled eggs, the cold makes the egg shrink slightly from the shell, so many cooks find them easier to peel.

How to use it

• Green vegetables for salads, crudités and stir-fries.
• Vegetables you will freeze, after you blanch them for the freezer.
• Tomatoes and peaches after a short boil, so the skins slip off.
• Boiled eggs, to stop the yolk turning gray-green.
• Pasta for cold salads. For hot pasta, do not shock it, as the sauce clings better to warm, starchy pasta.

Common mistakes

• Too little ice. The water warms up and the food keeps cooking.
• Leaving food in the water too long. Vegetables get waterlogged and lose flavor.
• Not drying. Water dilutes dressings and makes sauces spit when you reheat in oil.
• Shocking parboiled potatoes you plan to roast straight away. They roast better while still warm and steamy.