Onions along with shallots, leeks, chives and garlic, belong to the Allium family, which including wild varieties has some 325 members. All have the characteristic onion smell, which is caused by volatile acids just below the skin. Onions have been eaten for thousands of years. They are believed to have originally come from the Middle East and their easy cultivation suggests that their use spread quickly. By the Middle Ages onions were a common vegetable throughout Europe and would have been used in soups, stews and sauces when strong flavouring was preferred.

There are many classic recipes specifically for onion dishes so they can be appreciated in their own right. But there is hardly a recipe where onions, or Alliums, are not used. Gently fried until soft, or fried more fiercely until golden, they add a unique, savoury flavour to dishes. Raw onions are a useful source of fibre, Vitamin C and folic acid.

Nutritional Value

Nutrient Raw Cooked (Fried in Oil) Cooked (Baked)
Energy kJ 150 684 439
Kcal 36 164 103
Protein g 1.2 2.3 3.5
Carbohydrate g 7.9 14.1 22.3
Fat g 0.2 11.2 0.6

A good source of…

Nutrient Raw Cooked (Fried in Oil) Cooked (Baked)
Fibre One Tick One Tick
Vitamin E One Tick
Vitamin C One Tick One Tick
Thiamin One Tick
Vitamin B6 One Tick One Tick
Folic Acid One Tick

For more information on nutrition and the details given above, check out our nutrition page.

Preparing and Using

Onions, more than almost any other vegetable,keep well provided they are stored in a cool,dry place. Don’t store them in the fridge because they will go soft. Onions don’t keep well once they have been cut and will flavour any other foods close by. Unused segments of onions can be used to flavour soups and stocks.

As well as the outer brown leaves, remove the next layer of onion, as it is often dry or damaged. Unless slicing onions for stir-fries, for which it is customary to slice the onion into wedges, always slice the onion through the rings, widthways. Appliances such as a Robotcoupe processor or similar type of food preparation machine will make light work of chopping onions.

The volatile acids in onions are driven off during cooking, which is why cooked onion is never as strong as raw onion. The method of cooking used, even the way of frying an onion,affects its eventual taste. Boiled onion or chopped onion added neat to soups or casseroles has a strong, more raw taste.Frying or sautéing briefly, or sweating until soft and translucent gives a milder flavour. When fried until golden brown, onions develop a distinct flavour, both sweet and savoury, that is superb in curries and with grilled meats and is essential for French onion soup. Caramelised onion has a sweet warm taste.

Onions come in a variety of different colours and strengths, and for certain recipes,particular types of onion are needed. They are used in thousands of dishes all around the world and can be shallow-fried, deep-fried (in batter), braised, stuffed and baked, roasted,pickled, boiled, grilled, barbecued and eaten raw. For classic recipes such as onion tarts,French onion soup and sauce soubise, only onions are appropriate.

Onions are used in a mirepoix of vegetables to flavour soups, sauces and stocks. They can also be used to flavour breads, scones,savoury cakes and biscuits and pizza bases.They are used extensively in Indian cooking and are the basic ingredient in Balti sauces.Other Indian dishes such bhajis and pakoras are made with onion as a main ingredient.Onions can be added to mashed potato, used to flavour pilaff rice and a host of different salads. They can be grilled or barbecued on kebabs with meat or other vegetables.


For some Onion recipes, visit the Bord Bia website here

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Three secrets to making the best burgers – top quality mince, the onions sautéed till golden brown and cooked ahead of time and a good splash of chilli oil in the mixture.

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Mexican Chilli

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