Onion
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 shallot is a botanical variety of the onion which was classified as a separate species until 2011. The onion's close relatives include garlic, scallion, leek, and chives.
The genus contains several other species variously called onions and cultivated for food, such as the Japanese bunching onion Allium fistulosum, the tree onion Allium × proliferum, and the Canada onion Allium canadense. The name wild onion is applied to a number of Allium species, but A. cepa is exclusively known from cultivation. Its ancestral wild original form is not known, although escapes from cultivation have become established in some regions. The onion is most frequently a biennial or a perennial plant, but is usually treated as an annual and harvested in its first growing season.
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 that envelop a central bud at the tip of the stem. In the autumn, 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. The crop is prone to attack by a number of pests and diseases, particularly the onion fly, the onion eelworm, and various fungi which can cause rotting. Some varieties of A. cepa, such as shallots and potato onions, produce multiple bulbs.
Onions are cultivated and used around the world. As a food item, they are often served raw as a vegetable or part of a prepared savoury dish, but can be eaten cooked or used to make pickles or chutneys. They are pungent when chopped and contain certain chemical substances which may irritate the eyes.
Taxonomy and etymology
The onion plant, also known as the bulb onion or common onion, is the most widely cultivated species of the genus Allium. It was first officially described by Carl Linnaeus in his 1753 work Species Plantarum. Synonyms during its taxonomic history are:- Allium cepa var. aggregatum – G. Don
- Allium cepa var. bulbiferum – Regel
- Allium cepa var. cepa – Linnaeus
- Allium cepa var. multiplicans – L.H. Bailey
- Allium cepa var. proliferum – Regel
- Allium cepa var. solaninum – Alef
- Allium cepa var. viviparum – Mansf.
Cepa is commonly accepted as Latin for "onion"; the generic name Allium is the classical Latin name for garlic.
It has an affinity with Spanish: cebolla, Italian: cipolla, Polish: cebula, and the German Zwiebel. The English word "chive" is from the Old French chive, in turn from cepa.
Description
The onion is a biennial plant but is usually grown as an annual. Modern varieties typically grow to a height of. The leaves are yellowish- to bluish green and grow alternately in a flattened, fan-shaped swathe. They are fleshy, hollow, and cylindrical, with one flattened side. They are at their broadest about a quarter of the way up, beyond which they taper to blunt tips. The base of each leaf is a flattened, usually white sheath that grows out of the basal plate of a bulb. From the underside of the plate, a bundle of fibrous roots extends for a short way into the soil. As the onion matures, food reserves accumulate in the leaf bases, and the bulb of the onion swells.In the autumn, the leaves die back, and the outer scales of the bulb become dry and brittle, so the crop is normally harvested. If left in the soil over winter, the growing point in the middle of the bulb begins to develop in the spring. New leaves appear, and a long, stout, hollow stem expands, topped by a bract protecting a developing inflorescence. The inflorescence takes the form of a rounded umbel of white flowers with parts in sixes. The seeds are glossy black and triangular in cross-section. The average pH of an onion is around 5.5.
History
Humans have grown and selectively bred onions in cultivation for at least 7,000 years. The geographic origin of the onion is uncertain; ancient records of onion use span both eastern and western Asia. Domestication likely took place in West or Central Asia. Onions have been variously described as having originated in Iran, western Pakistan and Central Asia. The onion species Allium fistulosum and Allium tuberosum were domesticated in China around 6000 BC alongside other vegetables, grains, and fruits.Recipes using onions and other Allium species were recorded in cuneiform script on clay tablets in ancient Mesopotamia, around 2000 BC; the tablets are held in Yale University's Babylonian collection. The Assyriologist and "gourmet cook" Jean Bottero stated this was "a cuisine of striking richness, refinement, sophistication and artistry". The onion is mentioned in the Hebrew Bible; evidence of onions in ancient Israel comes from Chalcolithic Nahal Mishmar and from Bronze Age Jericho.
Ancient Egyptians revered the onion bulb, viewing its spherical shape and concentric rings as symbols of eternal life. Onions were used in Egyptian burials, as evidenced by onion traces found in the eye sockets of Ramesses IV. Pliny the Elder of the first century AD wrote about the use of onions and cabbage in Pompeii. He documented Roman beliefs about the onion's ability to improve ocular ailments, aid in sleep, and heal everything from oral sores and toothaches to dog bites, lumbago, and even dysentery. Archaeologists unearthing Pompeii long after its 79 AD volcanic burial have found gardens resembling those in Pliny's detailed narratives. According to texts collected in the fifth/sixth century AD under the authorial aegis of "Apicius", onions were used in many Roman recipes.
In the Age of Discovery, onions were taken to North America by the first European settlers in part of the Columbian exchange. They found close relatives of the plant such as Allium tricoccum readily available and widely used in Native American gastronomy. According to diaries kept by some of the first English colonists, the bulb onion was one of the first crops planted in North America by the Pilgrim fathers. Between 1883 and 1939, inventors in the United States patented 97 inventions meant to make onion-growing more efficient through automation.
Uses
Culinary
Three colour varieties of onions offer different possibilities for the cook:- Yellow or brown onions are sweet, with many cultivars bred specifically to accentuate this sweetness, such as Vidalia, Walla Walla, Cévennes, and Bermuda. Yellow onions turn a rich, dark brown when caramelised and are used to add a sweet flavour to various dishes, such as French onion soup.
- Red or purple onions, known for their sharp pungent flavour, are commonly cooked in many cuisines, and used raw and in grilling.
- White onions are mild in flavour; they have a golden colour when cooked and a particularly sweet flavour when sautéed.
Onions are commonly chopped and used as an ingredient in various hearty warm dishes, and may be used as a main ingredient in their own right, for example in French onion soup, creamed onions, and onion chutney. They are versatile and can be baked, boiled, braised, grilled, fried, roasted, sautéed, or eaten raw in salads. Onions are a major ingredient of some curries; the Persian-style dopiaza's name means "double onion", and it is used both in the dish's sour curry sauce and as a garnish. Onion powder is a seasoning made from finely ground, dehydrated onions; it is often included in seasoned salt and spice mixes.