What is an onion?
Onions are endlessly versatile and an essential ingredient in countless recipes. Native to Asia, these underground bulbs are prized all over the world for the depth and flavour they add to savoury dishes. Dry onions are fully matured, with juicy flesh and dry, papery skin and have a pungent flavour that becomes wonderfully sweet upon lengthy cooking.
Varieties of onion differ in size, strength and colour. The yellow onion is the most commonly known variety; it has pale golden skin, greenish-white flesh and a strong taste. Red onions are an attractive, milder alternative to the yellow onion with their shiny purple skin and red-tinged flesh. Shallots are a sub-species of onion; they are small and boast a delicate flavour integral to French cooking. Spring onions are immature onions pulled before the bulb is fully formed, and can be recognised by their long green leaves. Like red onions, they are fairly mild and often used raw in salads.
When chopped, onions produce a volatile, sulphur-rich oil that makes the eyes water. Over the years cooks have devised many ways to prevent this (freezing the onion or wearing goggles among them), but they are rarely completely effective. The best way is to not cut into the root of the onion, as this is where most of the oil resides.
Find out about the health benefits of onions and try our favourite onion recipes.
How to prepare onions
First, slice away the top of the onion (leave the root on), then remove the papery skin and any brown outer layers. To chop the onion, cut in half from top to bottom. Put the cut-side flat on the work surface, then make a series of cuts horizontally, then vertically, but without cutting through the root. Holding the onion very firmly, slice the onion. It should fall away in small pieces as you go. Continue cutting until you reach the root, which you can now discard.
To slice, trim the root off and a little off the base (to hold it steady on the chopping board), then cut away the slices moving from the root end towards the top. You can then separate each slice into rings, if you like.
All onions are best prepared just before use.
Watch our video guide on how to chop onions:
How to cook onions
Gently fry chopped or sliced onion (7-10 mins) then use as the base for pasta sauces, soups and stews. Cut into wedges and roast (40-50 mins). Cut into rings, batter and deep-fry (3 mins). Bake (20-30 mins).
Try thickly slicing onions, and coating in a batter before deep-frying to make onion rings for the perfect side dish to a burger or ribs. Fry onions slowly in butter until golden and caramelised before adding stock to make a rich onion gravy. Or use their layers to encase spiced lamb mince in our stuffed onions recipe. When onions are cooked for a long time they become sweet and sticky, great for making onion chutney, or a sticky onion & cheddar quiche.
How to store onions
Onions should be kept in a cool, dark, dry place. Spring onions can be stored in the fridge for up to a week.
Choose the best onions
Look for firm onions, with no soft spots, damp, or mouldy patches. Choose from the following, according to your recipe:
White onion: medium to large in shape, with a white papery skin and evenly white flesh. They have a strong flavour and are good for stuffing or baking; only use raw in salads if you want an assertive onion flavour.
Yellow/brown onion: a good all-purpose onion, with a light golden skin and yellow flesh.
Spanish onion: has a similarly coloured skin to a yellow/brown onion, but is usually bigger, as well as tasting sweeter and milder. These are good for omelettes, salsas and stir-fries.
Red onion: sizes vary, and they have a distinctive red/purple skin; the edge of each of its white rings is also tinged with red. The flavour is mild and quite sweet. Good for salads, marinades, salsas and roasts.
Alternatives to onions