Ingredient

Groundnut oil

Groundnut oil — peanut oil — is refined, neutral and unusually stable at high heat, which is why it is the traditional choice for wok cooking and deep-frying across much of Asia. It is also, unavoidably, made from a major allergen, and that has to be part of any decision to use it.

Why it suits high heat

Refined groundnut oil is high in monounsaturated fat and low in the polyunsaturates that oxidise readily, which makes it comparatively stable both in the bottle and in a hot pan. It also holds its temperature well, recovering quickly when cold food goes in.

That recovery matters more than most people realise. Food dropped into oil that then loses its heat absorbs fat instead of crisping, which is the mechanism behind almost all greasy fried food. An oil that stays hot gives a drier, crisper result.

The refined kind is essentially neutral in flavour, so it does not compete with whatever is being cooked in it. The roasted kind is a different product entirely.

Refined and roasted

Refined groundnut oil

Pale, neutral, stable. The frying oil. What "groundnut oil" on a bottle almost always means.

Roasted peanut oil

Amber, strongly nutty, sold in small bottles. A seasoning oil for dressings and finishing, not for frying.

The allergen

Peanut is one of the fourteen allergens that must be declared in the UK. Highly refined oils are treated differently in labelling rules, but this is a food-safety and labelling matter — follow Food Standards Agency guidance and always ask before cooking for others.

Reusing

Strains and reuses well, better than most. Discard when it darkens, foams or smells off.

Alternatives for the same job

High-oleic sunflower oil and refined rapeseed both fry well and carry no peanut allergen.

What it is for

• Wok cooking, where the heat is fierce and the oil must not smoke or taste of anything.
• Deep-frying, particularly anything battered, where temperature recovery decides how greasy the result is.
• Shallow-frying fish or chicken, where a neutral flavour matters.
• Chips, where its stability suits the double-fry method.
• Roasted peanut oil in a dressing, with rice vinegar and soy, for a noodle or cabbage salad.
• Roasted peanut oil drizzled over a satay or a peanut sauce to reinforce the flavour.
• Not for a household with a peanut allergy, in any form. The alternatives above do the same job.

Deep-frying with it

1. Use a deep, heavy pan filled no more than a third, or a proper fryer.
2. Bring the oil up steadily. Rushing it gives uneven temperature and scorched spots.
3. Fry in small batches so the temperature does not collapse when the food goes in.
4. Let the oil come back up between batches. This is the single most useful habit for crisp results.
5. Drain on a rack rather than on paper. Paper traps steam underneath and softens the crust.
6. Cool completely, then strain through muslin into a clean labelled jar for reuse.
7. Never leave a pan of hot oil unattended, and never add water to it.

Common questions