The onion, also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus Allium. The onion plant has a fan of hollow, bluish-green leaves and its bulb at the base of the plant begins to swell when a certain day-length is reached. The bulbs are composed of shortened, compressed, underground stems surrounded by fleshy modified scale (leaves) that envelop a central bud at the tip of the stem. In the autumn (or in spring, in the case of overwintering onions), the foliage dies down and the outer layers of the bulb become more dry and brittle. The crop is harvested and dried and the onions are ready for use or storage.
Onions are cultivated and used around the world. As a food item, they are usually served cooked, as a vegetable or part of a prepared savoury dish, but can also be eaten raw or used to make pickles or chutneys. They are pungent when chopped and contain certain chemical substances which may irritate the eyes.
Types of Onion:
Yellow or brown onions (called "red" in some European countries) are sweeter and are the onions of choice for everyday use in European cuisine, with many cultivars bred specifically to demonstrate this sweetness.Yellow onions turn a rich, dark brown when caramelised and give French onion soup its sweet flavour.
Red or purple onions ("purple" is used in some European countries) are known for their sharp pungent flavor and are the onions of choice for everyday use in Asian cuisine. They are also used raw and in grilling.
White onions are traditional in classic Mexican cuisine, and are milder in flavor; they have a golden colour when cooked and a particularly sweet flavour when sautaed.
