Cookbook:Onion
Cookbook | Cookbook:Vegetables
Onion in the general sense can be used for any plant in the genus Allium but used without qualifiers usually means Allium cepa, also called the garden onion. Onions (usually but not exclusively the bulbs) are edible with a distinctive strong flavour and pungent odour which is mellowed by cooking. They generally have a papery outer skin over a fleshy, layered inner core. Used worldwide for culinary purposes, they come in a wide variety of forms and colors (but generally brown, white or purple).
The common brown onion tends to have a very pungent odour, and it makes the eyes water. Some varieties have more or less of the eye-watering chemicals, which also makes them taste milder. 'Spanish onions' (the large white onions with a purple skin and purple flecks) are much milder than brown onions, making them more suitable for raw use in salads.
Onions may be grown from seed or very commonly from "sets". Onion sets are produced by sowing seed very thickly one year, resulting in stunted plants which produce very small bulbs. These bulbs are very easy to set out and grow into mature bulbs the following year, but they have the reputation of producing a less durable bulb than onions grown directly from seed and thinned.
Either planting method may be used to produce spring onions or green onions, which are just onions harvested while immature, although "green onion" is also a common name for the welsh onion, Allium fistulosum which never produces dry bulbs and the 'Spring onions' used in Asian cooking are an entirely different variety which never grows a full bulb.
Related species
The genus Allium is a large one, and most of the species are considered to be "onions" in the looser sense. Commonly raised vegetable alliums include the leeks, garlic, elephant garlic, chives, shallots, welsh onions and garlic chives.
The wild onion (allium ursinum) is collected in the wild, its leaves and bulbs used as food.