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Onion: the story on HearLore | HearLore
Onion
The onion is the only vegetable that can make a grown adult weep without any emotional cause, a biological defense mechanism that has shaped human history for seven millennia. This pungent bulb, scientifically known as Allium cepa, has been cultivated since at least 2000 BC, with ancient cuneiform tablets from Mesopotamia recording recipes that describe a cuisine of striking richness and sophistication. The plant's journey from the wild grasses of Central Asia to the dinner plates of the modern world is a story of human ingenuity and biological adaptation. Ancient Egyptians revered the onion's concentric rings as a symbol of eternal life, placing them in the eye sockets of pharaohs like Ramesses IV to ensure their vision in the afterlife. Pliny the Elder, writing in the first century AD, documented Roman beliefs that onions could cure everything from dog bites to dysentery, a testament to the vegetable's perceived medicinal power in antiquity. The very act of chopping an onion releases syn-propanethial-S-oxide, a volatile gas that triggers the lacrimal glands to produce tears, a chemical reaction that has likely been the source of countless kitchen frustrations since the first human sliced into a bulb.
A Botanical Mystery
Despite being the most widely cultivated species of the genus Allium, the onion's ancestral wild form remains a mystery to botanists, existing exclusively in cultivation today. The plant is a biennial that is almost always treated as an annual, harvested in its first growing season before the foliage dies down and the outer layers become dry and brittle. The bulb itself is a compressed underground stem surrounded by fleshy modified scales that envelop a central bud, a structure that swells only when a specific day-length is reached. This photoperiod sensitivity divides the crop into long-day, intermediate-day, and short-day varieties, each requiring precise hours of sunlight to trigger bulb formation. Modern varieties can grow to heights of several inches, with leaves that are yellowish to bluish green, hollow, and cylindrical, tapering to blunt tips. The average pH of an onion is around 5.5, and the plant contains low amounts of essential nutrients, providing only 40 kilocalories per 100 grams while contributing significant savory flavor to dishes.
The Chemical Defense
The stinging sensation that causes uncontrollable tears when cutting an onion is the result of a complex chain of chemical reactions designed to protect the plant from predators. When cells are damaged by a knife, enzymes called alliinases break down amino acid sulfoxides to generate sulfenic acids, which are then rapidly acted upon by a second enzyme known as the lacrimatory factor synthase. This process produces syn-propanethial-S-oxide, a gas that diffuses through the air to activate sensory neurons in the eye, forcing the lacrimal glands to produce tears to dilute and flush out the irritant. In 2008, the New Zealand Institute for Crop and Food Research created no tears onions by genetically modifying the plant to prevent the synthesis of this specific enzyme, though some consumers found the flavor inferior due to the impediment of sulfur ingestion. By early 2018, Bayer released the first commercially available LFS-silenced onions under the name Sunions, the product of 30 years of cross-breeding without genetic modification, offering a solution to the weeping cook.
When was the onion first cultivated and what evidence exists for its early use?
The onion has been cultivated since at least 2000 BC, with ancient cuneiform tablets from Mesopotamia recording recipes that describe a cuisine of striking richness and sophistication. This pungent bulb, scientifically known as Allium cepa, has been cultivated since at least 2000 BC, with ancient cuneiform tablets from Mesopotamia recording recipes that describe a cuisine of striking richness and sophistication.
What chemical reaction causes onions to make people cry?
The stinging sensation that causes uncontrollable tears when cutting an onion is the result of a complex chain of chemical reactions designed to protect the plant from predators. When cells are damaged by a knife, enzymes called alliinases break down amino acid sulfoxides to generate sulfenic acids, which are then rapidly acted upon by a second enzyme known as the lacrimatory factor synthase to produce syn-propanethial-S-oxide.
Who created the first no tears onions and when were they released commercially?
In 2008, the New Zealand Institute for Crop and Food Research created no tears onions by genetically modifying the plant to prevent the synthesis of this specific enzyme. By early 2018, Bayer released the first commercially available LFS-silenced onions under the name Sunions, the product of 30 years of cross-breeding without genetic modification.
Which country produces the most onions globally and what was the total production in 2022?
China leads global onion production which accounted for 17% of the total, with global production reaching 5.0 million tonnes in 2022. The top global producers include India, the United States, and Turkey, with Mali, Angola, and Japan serving as secondary producers.
Why were onions placed in the eye sockets of pharaohs like Ramesses IV?
Ancient Egyptians revered the onion's concentric rings as a symbol of eternal life, placing them in the eye sockets of pharaohs like Ramesses IV to ensure their vision in the afterlife. The plant's journey from the wild grasses of Central Asia to the dinner plates of the modern world is a story of human ingenuity and biological adaptation.
Are onions toxic to animals and what specific damage do they cause?
While onions are a staple food for humans, they are toxic to animals including dogs, cats, and guinea pigs, causing damage to their red blood cells and leading to anemia. The plant can also accumulate heavy metals such as cadmium and lead, particularly when cultivated in contaminated soils, leading to regulatory limits set by the European Union.
Onions are produced in the second largest quantity of any vegetable crop after tomatoes, with global production reaching 5.0 million tonnes in 2022, led by China which accounted for 17% of the total. The top global producers include India, the United States, and Turkey, with Mali, Angola, and Japan serving as secondary producers. The plant's versatility allows it to be eaten raw, cooked, pickled, or dried, with different varieties offering distinct flavor profiles ranging from the sweet Vidalia and Walla Walla to the sharp red and purple types. Yellow onions turn a rich, dark brown when caramelized and are used to add sweetness to dishes like French onion soup, while white onions are mild and turn golden when cooked. The crop is prone to attack by pests such as the onion fly and the onion eelworm, as well as diseases like white rot and neck rot, requiring careful management of soil conditions and storage environments to prevent loss.
Cultures and Myths
The onion has permeated human culture in ways both profound and absurd, appearing in the Odyssey where Homer compared a tunic to the skin of a dried onion, a comparison that Theopompus found ridiculous yet may have hinted at Penelope's sorrow. In the 10th century, the Exeter Book contained a riddle about an onion with sexual overtones, describing a wondrous creature that stands in a bed and makes the eye wet. The name Big Onion was formerly used for New York City before it became the Big Apple, and Chicago adopted the moniker due to the native American name for the city meaning a type of wild onion. Onion Johnnies were Breton farmers who traveled from Roscoff to Britain selling strings of distinctive pink onions door to door, a tradition that persists in the collective memory of the region. In India, when onion prices soared in 2015, the public responded with puns and jokes, highlighting the vegetable's central role in the national diet and economy.
Varieties and Hybrids
The diversity within the common onion group is vast, encompassing plants that form large single bulbs, salad onions, and pickling onions, with variations in photoperiod, storage life, and skin color. The Aggregatum group contains shallots and potato onions, which form aggregate clusters of several bulbs from a master plant, with shallots being the most important subgroup cultivated commercially. The I'itoi onion is a prolific multiplier onion cultivated in the Baboquivari Peak Wilderness in Arizona, known for its shallot-like flavor and ability to grow in hot, dry climates. Hybrids such as the tree onion or Egyptian onion are the result of crossing Allium cepa with Allium fistulosum, producing bulblets in the umbel instead of flowers. The triploid onion, a hybrid species with three sets of chromosomes, includes clones like Ljutika in Croatia and Pran in the India-Kashmir region, which are grown locally due to their unique genetic characteristics.
Toxicity and Science
While onions are a staple food for humans, they are toxic to animals including dogs, cats, and guinea pigs, causing damage to their red blood cells and leading to anemia. The plant can also accumulate heavy metals such as cadmium and lead, particularly when cultivated in contaminated soils, leading to regulatory limits set by the European Union. In science education, onion epidermis cells are commonly used to teach the use of a microscope because they form a single layer that is easy to separate and observe under low magnification. Onion skins can be boiled to make an orange-brown dye, and onion oil is authorized for use in the European Union as a pesticide against carrot fly in umbelliferous crops. The chemical compounds within the onion, particularly polyphenols and anthocyanins, are under basic research to determine their possible biological properties in humans, with red onions containing at least 25 different compounds representing 10% of total flavonoid content.