Blanching

What it does

Brief heat does three useful things to a green vegetable. It brightens the colour, by driving out the gas trapped between cells that was dulling the chlorophyll. It softens just enough to take the raw edge off. And it deactivates enzymes that would otherwise keep degrading the colour, texture and flavour over time — which is why blanching is a required step before freezing vegetables.

The cold plunge afterwards is not optional. Without it the vegetable carries on cooking in its own residual heat, the colour goes olive, and you have wasted the exercise. Iced water stops the process dead, and it is what distinguishes blanching from simply boiling something briefly.

How to do it

1. Bring a large pan of water to a rolling boil and salt it well. Volume matters — a small pan drops out of the boil when the vegetables go in.
2. Have a bowl of iced water ready beside the hob before anything goes into the pan. This is the step people skip and then regret.
3. Add the vegetables in a quantity the water can handle. In batches if necessary.
4. Cook briefly — thirty seconds for spinach or peas, one to two minutes for beans, two to three for broccoli, longer for dense roots.
5. Lift straight into the iced water with a slotted spoon or a spider.
6. Once cold, drain thoroughly and dry. Wet vegetables will not fry or roast afterwards.

What to blanch, and why

Green beans, broccoli, asparagus, peas

For colour and to part-cook in advance. Finish in butter or a pan at the last minute.

Spinach and greens

To wilt them evenly before squeezing and using in a filling or a side.

Vegetables for freezing

Essential. Unblanched frozen vegetables degrade in colour and flavour over months because their enzymes stay active.

Almonds and pistachios

Thirty seconds and the skins slip off.

Tomatoes and peaches

A scored cross and twenty seconds loosens the skin.

Potatoes before roasting

A longer parboil rather than a true blanch, and no ice bath — you want them dry and steaming.

Bacon lardons and bones

To remove excess salt or scum before the main cooking.

Why it is worth the trouble

• It lets you cook vegetables in advance, which is the only way to get several things onto a table hot at once.
• It gives better colour than any other method, and colour is most of how a vegetable dish reads.
• It removes the risk of overcooking at the last minute, which is when kitchens are most chaotic.
• It improves roasting and frying, because a blanched vegetable needs only browning rather than cooking through.
• It costs nothing except a bowl of ice.

What blanching is actually for

• Setting colour. A brief boil then an ice bath fixes green vegetables bright and stops them dulling. This is why restaurant greens look as they do.
• Cooking ahead. Blanched and refreshed vegetables can be finished in butter in ninety seconds at the last minute, which solves most timing problems.
• Before freezing. It deactivates the enzymes that would otherwise degrade colour, texture and flavour in the freezer over months.
• Loosening skins. Thirty seconds for tomatoes, peaches and almonds, and the skins slip off.
• Taking the edge off. Removes harshness from raw onion, bitterness from some greens, and excess salt from bacon or salted anchovy.
• The ice bath is not optional for any of these. Without it the vegetable carries on cooking in its own heat and the point is lost.

Common questions