Ingredient

Potato

Almost every potato disappointment is one decision made wrong: floury where you needed waxy, or the reverse. A potato is mostly starch and water, and how much starch it holds decides whether it collapses into fluff or holds its shape.

Floury and waxy

A floury potato — Maris Piper, King Edward, Russet, Desiree — has a lot of starch and relatively little water. When it cooks, the starch granules swell and the cells separate, so the flesh goes dry, light and mealy and falls apart readily. That is exactly what you want for mash, roast potatoes and chips, and exactly what you do not want in a salad.

A waxy potato — Charlotte, Anya, new potatoes, most small ones — has less starch and more moisture and sugar. The cells hold together, so it stays firm, slices cleanly and keeps its edges. Right for salads, gratins, boiling and anything that has to be handled after cooking.

Some, like Yukon Gold or Wilja, sit between the two and do most jobs adequately. If a shop sells nothing else, they are the safe buy.

Which potato for which job

Roasting

Floury. The fluffy outside is what crisps; a waxy potato roasts to something smooth and disappointing.

Mashing

Floury. And mash it while hot, gently, with a ricer or a masher — never a food processor, which shears the starch into glue.

Chips and wedges

Floury. Low starch means a chip that browns without going fluffy inside.

Boiling and salads

Waxy. They stay in one piece and take dressing without disintegrating.

Gratin and dauphinoise

Waxy or all-purpose, sliced thin. Floury ones dissolve into the cream.

Soup

Floury if you want it to thicken itself; waxy if you want distinct pieces.

Roast potatoes that actually crisp

The whole method is about creating a rough, starchy surface and then getting hot fat to it.

1. Peel floury potatoes and cut them into large, uneven chunks. Uneven is deliberate — the corners are where the crisp comes from.
2. Boil in well-salted water until the outsides are genuinely soft and a fork goes in easily. Slightly overcooked is better than undercooked here.
3. Drain thoroughly and let them steam dry in the colander for a couple of minutes. Surface water is the enemy of crisping.
4. Shake the colander hard until the outsides go fluffy and roughed up. This is the step people skip and it is the one that matters most.
5. Get the fat properly hot in the tin first, then add the potatoes in a single layer with room around each one. Crowding steams them.
6. Turn once or twice. Do not turn constantly, and do not season with anything sugary until near the end.

The common failures

• Gluey mash — over-worked, or made in a processor. The cell walls have been torn and the starch released. Not fixable; next time use a ricer and stop early.
• Soggy roast potatoes — wet surfaces, a crowded tin, or fat that was not hot. See soggy roast potatoes.
• Falling apart when boiled — a floury potato doing what floury potatoes do. Use waxy, start them in cold water, and simmer rather than boil hard.
• Green patches — light exposure. The green itself is chlorophyll and harmless, but it indicates the presence of compounds that taste bitter, so cut green parts away generously.
• Grey after boiling — a reaction between iron and compounds in the potato. Harmless. A little acid in the water reduces it.

Storing them

• Cool, dark, dry and airy. A paper or hessian sack, not a plastic bag, and not a sealed cupboard.
• Not in the fridge. Cold converts some of the starch to sugar, which makes the potato taste sweet and — more practically — makes it brown far too fast and unevenly when fried or roasted.
• Away from onions. Each speeds the other up.
• Sprouts mean the potato is trying to grow. Rub them off if small; if the potato is soft and shrivelled, it is past it.

Common questions