Onion
Carl Linnaeus first described the onion plant in his 1753 work Species Plantarum. The scientific name Allium cepa comes from Latin, where cepa means onion and Allium refers to garlic. Eric Block noted this classification in his 2010 book Garlic and Other Alliums: The Lore and the Science. Related species include garlic, scallion, leek, and chives. The shallot was classified as a separate species until 2011 when it became a botanical variety of the onion. Synonyms during its taxonomic history included Allium cepa var. aggregatum and Allium cepa var. bulbiferum. A. cepa is known exclusively from cultivation, though related wild species occur in Central Asia and Iran. The most closely related include A. vavilovii from Turkmenistan and A. asarense from Iran. The English word chive derives from Old French chive, which traces back to cepa. Spanish uses cebolla, Italian uses cipolla, Polish uses cebula, and German uses Zwiebel for this vegetable.
The onion plant has a fan of hollow, bluish-green leaves that grow alternately in a flattened, fan-shaped swathe. Modern varieties typically grow to a height of about one meter. The leaves are fleshy, hollow, and cylindrical with one flattened side. They are at their broadest about a quarter of the way up before tapering to blunt tips. The base of each leaf forms a flattened white sheath growing out of the basal plate of a bulb. From the underside of the plate, fibrous roots extend short distances into the soil. As the onion matures, food reserves accumulate in the leaf bases causing the bulb to swell. In autumn, the leaves die back and outer scales become dry and brittle. If left in soil over winter, the growing point develops in spring. New leaves appear while a long stout hollow stem expands topped by bract protecting developing inflorescence. The inflorescence takes form as rounded umbel of white flowers with parts in sixes. Seeds are glossy black and triangular in cross-section. Average pH of an onion is around 5.5.
Humans have grown and selectively bred onions for at least 7,000 years. Ancient records span both eastern and western Asia though geographic origin remains uncertain. Domestication likely occurred in West or Central Asia. Recipes using onions appeared on cuneiform tablets in ancient Mesopotamia around 2000 BC held in Yale University's Babylonian collection. Assyriologist Jean Bottero described this cuisine as having striking richness and sophistication. Onions were mentioned in Hebrew Bible with evidence from Chalcolithic Nahal Mishmar and Bronze Age Jericho. Ancient Egyptians revered the onion bulb viewing its spherical shape and concentric rings as symbols of eternal life. Onion traces found in eye sockets of Ramesses IV confirmed their use in Egyptian burials. Pliny the Elder wrote about onion use in Pompeii during first century AD documenting beliefs about improving ocular ailments and healing oral sores. Archaeologists unearthing Pompeii after its 79 AD volcanic burial found gardens resembling those in Pliny's narratives. Texts collected under Apicius authorial aegis show onions used in many Roman recipes. Pilgrim fathers planted bulb onions among first crops in North America during Age of Discovery.
Yellow or brown onions are sweet with cultivars like Vidalia, Walla Walla, Cévennes, and Bermuda bred to accentuate sweetness. Yellow onions turn rich dark brown when caramelized for dishes like French onion soup. Red or purple onions offer sharp pungent flavor commonly cooked in many cuisines or eaten raw. White onions provide mild flavor turning golden when cooked with particularly sweet taste when sautéed. Young plants harvested before bulbing occur serve whole as spring onions or scallions. Summer onions harvested after bulbing begins but before maturity differ from true pearl onions which are different species. Pearl boiler and pickler onions mature at smaller sizes often preserved in vinegar as long-lasting relish. Onions may be baked boiled braised grilled fried roasted sautéed or eaten raw in salads. Onion powder seasoning made from finely ground dehydrated onions included in seasoned salt mixes. Persian-style dopiaza means double onion using both sour curry sauce and garnish components. Three color varieties offer distinct possibilities for cooks worldwide.
Most onion cultivars contain about 89% water and 9% carbohydrates including 4% sugar and 2% dietary fiber. Energy value reaches 166 kilojoules or 40 kilocalories per 100 grams. Shallots have highest polyphenol levels six times amount found in Vidalia onions. Yellow onions possess highest total flavonoid content eleven times higher than white onions. Red onions contain considerable anthocyanin pigments representing 10% of total flavonoid content. Freshly cut onions produce stinging sensation causing uncontrollable tears through syn-propanethial-S-oxide release. Chopping damages cells releasing enzymes called alliinases breaking down amino acid sulfoxides generating sulfenic acids. Specific sulfenic acid rapidly acted on by lacrimatory factor synthase producing irritating gas diffusing through air activating sensory neurons. Lacrimal glands produce tears to dilute irritant. Eye irritation minimized by cutting under running water or submerged basin leaving root end intact reduces irritation due to higher sulfur concentration at base. In 2008 New Zealand Institute for Crop and Food Research created no tears onions preventing lachrymatory factor synthesis. Bayer released first commercially available LFS-silenced Sunions crop yield in early 2018 after 30 years cross-breeding without genetic modification.
Onions best cultivated in fertile well-drained soils with sandy loams low in sulfur preferred over clay-rich high sulfur varieties. Bulbing onions day-length sensitive beginning growth only after daylight hours surpass minimal quantity. Traditional European onions called long-day requiring 14 hours or more daylight produce bulbs. Southern European North African intermediate-day types require 12-13 hours daylight. Short-day onions developed recently planted mild-winter areas autumn forming bulbs early spring requiring 11-12 hours daylight. Onions cool-weather crops grown USDA zones 3 to 9 bolt meaning flower stem grows under hot temperatures. Grown from seeds or partially grown bulbs sets starter bulbs. Onion seeds short-lived fresh germinate effectively sown shallow rows drills 12 to 18 inches apart. Routine care keeps rows free competing weeds especially when plants young. Shallow-rooted plants need little water established. Bulbing takes place after 12 to 18 weeks harvested leaves died back naturally stored cool ventilated place. Most serious pests include onion fly stem bulb eelworm white rot neck rot diseases affecting foliage rust smut downy mildew white tip disease. Onion fly Delia antiqua lays eggs leaves stems ground close plants attracted crop smell damaged tissue liable occur after thinning.
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Common questions
When did Carl Linnaeus first describe the onion plant?
Carl Linnaeus first described the onion plant in his 1753 work Species Plantarum. The scientific name Allium cepa comes from Latin, where cepa means onion and Allium refers to garlic.
Where is the geographic origin of the onion plant located?
Domestication likely occurred in West or Central Asia though ancient records span both eastern and western Asia. Related wild species occur in Central Asia and Iran including A. vavilovii from Turkmenistan and A. asarense from Iran.
How many years have humans grown and selectively bred onions for food?
Humans have grown and selectively bred onions for at least 7,000 years. Recipes using onions appeared on cuneiform tablets in ancient Mesopotamia around 2000 BC held in Yale University's Babylonian collection.
What causes freshly cut onions to make people cry?
Freshly cut onions produce stinging sensation causing uncontrollable tears through syn-propanethial-S-oxide release. Chopping damages cells releasing enzymes called alliinases breaking down amino acid sulfoxides generating sulfenic acids that rapidly act on by lacrimatory factor synthase producing irritating gas.
When did Bayer release the first commercially available no tears onion crop?
Bayer released first commercially available LFS-silenced Sunions crop yield in early 2018 after 30 years cross-breeding without genetic modification. In 2008 New Zealand Institute for Crop and Food Research created no tears onions preventing lachrymatory factor synthesis.