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Onion

2007 Schools Wikipedia Selection. Related subjects: Food and agriculture

                    iOnion
   Onions
   Onions
           Scientific classification

   Kingdom:  Plantae
   Division: Magnoliophyta
   Class:    Liliopsida
   Order:    Asparagales
   Family:   Alliaceae
   Genus:    Allium
   Species:  A. cepa

                                Binomial name

   Allium cepa
   L.

   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 and sweetened 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 colours.

   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.

   Onions are frequently used in school science laboratories because they
   have particularly large cells which are easily visible even through
   rather low-end optical microscopes.

History

   Onion fields near Elba, New York
   Enlarge
   Onion fields near Elba, New York

   It is thought that bulbs from the onion family have been utilised as a
   food source for millennia. In Palestinian Bronze Age settlements,
   traces of onion remains were found alongside fig and date stones dating
   back to 5000 BC. It would be pure conjecture to suggest these were
   cultivated onions. The archaeological and literary evidence suggests
   cultivation probably took place around two thousand years later in
   ancient Egypt. This happened alongside the cultivation of leeks and
   garlic and it is thought that workers who built the pyramids were fed
   radishes and onions.

   The onion is easily grown, transportable, and has good storage
   qualities. Egyptians worshipped it, believing that its spherical shape
   and concentric rings symbolized eternal life. Onions were even used in
   Egyptian burials as evidenced by onion traces being found in the eye
   sockets of Ramesses IV. They believed that if buried with the dead, the
   strong scent of onions would bring breath back to the dead. The onion
   then made its way to Greece where athletes ate large quantities of
   onion because it would lighten the balance of blood. Roman gladiators
   were also rubbed down with onion to firm up their muscles. In the
   Middle Ages onions were such an important food that people would pay
   for their rent with onions and even give onions as gifts. Doctors were
   also known to prescribe onions to end headaches, snakebites and hair
   loss. The onion was introduced to North America by Christopher Columbus
   on his 1493 expedition to Haiti.

   Onions are a fundamental part of much Indian cooking and are called
   Pyaaz in Hindi. It is a staple food in India, both due to its use as a
   common base for curries and as the cheapest and most widely available
   vegetable for the poor.

   Onions are available in fresh, frozen, canned, and dehydrated forms.
   Onions can be used, usually chopped or sliced, in almost every type of
   food, including cooked foods and fresh salads, and as a spicy garnish;
   they are rarely eaten on their own but usually act as accompaniment to
   the main course.

   Depending on the variety, an onion can be sharp and pungent or mild and
   even sweet.

   They appear to be at least somewhat effective against colds, heart
   disease, diabetes, osteoporosis, and other diseases and contain
   anti-inflammatory, anticholesterol, anticancer, and antioxidant
   components such as quercetin.

   In many parts of the undeveloped world, onions are used to heal
   blisters and boils. In the United States, products that contain onion
   extract (such as Mederma) are used in the treatment of topical scars.

Onions and crying

   As onions are sliced, cells are broken open. Onion cells have two
   sections, one with enzymes called alliinases, the other with sulfides (
   amino acid sulphoxides). The enzymes break down the sulphides and
   generate sulphenic acids. Sulphenic acids are unstable and decompose
   into a volatile gas called syn-propanethial-S-oxide. The gas then
   dissipates through the air and eventually reaches one's eye, where it
   will react with the water to form a dilute solution of sulphuric acid.
   The sulphuric acid irritates the nerve endings in the eyes, making them
   sting. The tear glands then produce tears to dilute and flush out the
   irritant.

   A firm in Toronto, Canada, attempted to utilize this property of onions
   in the manufacture of a form of tear gas for civilian use. It was
   marketed in 1991 but was unsuccessful as it had an effective shelf life
   of only three months.

   Supplying ample water to the reaction prevents the gas from reaching
   the eyes. Therefore cutting the onions under running tap water or
   completely under water can help, as can rinsing the onion and leaving
   it wet while cutting. Chilling the onion will prevent the enzymes from
   activating, which will limit the amount of gas generated. Some people
   will freeze their knives to enhance this effect. Finally, using a sharp
   knife will limit the cell damage, and therefore prevent the release of
   enzymes.

   Different species of onions will release different amounts of sulphenic
   acids, thus some will cause more tear formation and irritation than
   others.

   The characteristic odour of onions can be removed with lemon.

Types of onion (Allium cepa)

   Two colours of onion

                       Yellow Onions

                                    Flower head of a yellow onion
     * Bulb onions - Grown from seed (or onion sets), bulb onions range
       from the pungent varieties used for dried soups and onion powder to
       the mild and hearty Sweet onions, such as the Vidalia from Georgia
       or Walla Walla from Washington that can be sliced and eaten on a
       sandwich instead of meat.
     * Multiplier onions - Raised from bulbs which produce multiple
       shoots, each of which forms a bulb.
          + Shallot (most of the types in the markets are Allium cepa)
          + Potato onion
     * Tree onions or Egyptian onions - These produce bulblets in the
       flower head, and are the result of hybridisation between Allium
       cepa and welsh onions.

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 Chinese chives. There are also species, such as Allium moly,
   grown for ornament.

   Several species of Allium, including A. canadense and A. diabolense,
   can be collected in the wild and their leaves and bulbs used as food.

In Language

   In the English vernacular, "an onion" is a difficult situation, the use
   stemming from the onion's tendency to irritate or inflame the eyes.
   Conversely, the term "onion" can be used to describe any state of
   being, as in the phrase, "[someone] really dices my onion!"

   Retrieved from " http://en.wikipedia.org/wiki/Onion"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
