Parboiling

Two environments, one piece of food

A raw potato put straight into a hot oven has to cook through by dry heat. By the time the middle is soft the outside is leathery, because dry heat dehydrates the surface long before it penetrates.

Parboiling cooks the inside in water, which conducts heat far better than air and cannot exceed boiling point, so the middle softens without the outside drying. The oven then has one job — crisping a surface that is already cooked — and it does that very well.

The second benefit is specific and important: boiling roughens the surface. A parboiled potato shaken in the pan develops a fluffy, broken exterior with a huge surface area, and that is what turns crisp. A smooth raw potato has nothing to crisp.

Parboiling potatoes for roasting

The canonical example, and worth doing properly.

1. Peel and cut floury potatoes — Maris Piper, King Edward, Rooster — into even large chunks.
2. Start them in cold salted water and bring to the boil, so they cook evenly rather than overcooking at the edges.
3. Simmer for eight to twelve minutes, until the outside is soft when pierced and the middle still has resistance. A knife should meet some grip at the centre.
4. Drain thoroughly and let them steam dry in the colander for a minute.
5. Put them back in the dry pan, put the lid on and shake it hard. The edges break up into a rough floury surface. This step is the whole trick.
6. Tip them into hot fat in a preheated tin, in a single layer with space between them.
7. Roast without turning for the first thirty minutes, then turn once.

Other things worth parboiling

Chips

Simmered then dried then fried, which is the basis of every good chip recipe.

Root vegetables for roasting

Carrot, parsnip and swede all benefit, though less dramatically than potatoes.

Ribs before barbecuing or roasting

Renders some fat and shortens the finish. Contested — some cooks argue it costs flavour.

Dense vegetables in a stir-fry

Broccoli stems, carrot, green beans. Thirty seconds so they finish at the same time as everything else.

Rice for a biryani

Cooked to about seventy per cent, then layered and steamed.

Pasta for a baked dish

Undercooked deliberately so it finishes in the sauce without going to mush.

Parboiling against blanching

The words overlap and the intentions differ.

• Parboiling part-cooks food that will be finished by another method. The aim is a head start.
• Blanching is a brief dip, usually followed by iced water, to set colour, loosen skins, deactivate enzymes or prepare for freezing.
• Blanching is shorter — seconds to a couple of minutes, against five to fifteen for parboiling.
• Blanching usually gets refreshed; parboiling usually does not, because you want the residual heat.
• Both use a lot of well-salted water, so the temperature recovers fast when the food goes in.
• Neither is a substitute for the other. A blanched potato will not roast well and a parboiled green bean is overcooked.

Common questions