Vegetable oils

It usually means a mild-tasting, refined oil made from one or more plants, often rapeseed, sunflower or soya. The exact blend can differ, so it is not a single oil with one flavour or cooking temperature.

For deep-frying, choose a refined oil labelled suitable for high-heat cooking, such as refined rapeseed or sunflower oil. Keep the oil around 170–180 °C; if it smokes, turn down the heat.

Yes, if it has not overheated or picked up a burnt smell. Let it cool, strain out crumbs and store it in a clean, sealed container; discard it if it turns very dark, thick or foamy.

Keep the bottle tightly closed in a cool, dark cupboard, away from the oven or hob. Light, warmth and air make oil lose freshness faster; follow any storage directions on the bottle.

Usually, yes: use about 80 g of oil for every 100 g of butter, as butter contains some water and milk solids. Oil makes cakes moist, but it will not give pastry the same firm, flaky texture as butter.

Yes, especially in roasting, sauces and baking. Extra-virgin olive oil has a distinct flavour, so use it when you want that taste; a mild refined olive oil is a closer match for neutral vegetable oil.

Not necessarily. Many vegetable oils come from seeds, such as sunflower, rapeseed or soya, but vegetable oil is a broad label and can also refer to blends or oils from other plant parts.

Yes. Choose a fresh, mild-tasting oil so it does not overpower the other ingredients. Add it gradually while whisking the egg yolk, mustard and lemon juice or vinegar to help the mayonnaise emulsify.