Onion
- For the parody newspaper, see The Onion. For the computer networking technique, see Onion Routing.
| Onion | ||||||||||||||
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| Allium cepa L. |
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 through an optical microscope. See how to prepare an onion cell slide for details.
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2 Related species 3 External links 4 References |
As onions are sliced, cells are broken open. Onion cells have two sections, one with enzymes called allinases, the other with sulfides. When the enzymes mix with the sulfides (amino acid sulfoxides), sulfenic acids are formed. Sulfenic acid is unstable and decomposes into a volatile gas called syn-ropanethial-S-oxide. The gas then dissapates through the air and eventually reaches one's eye, where it will react with the water to form a mild sulfuric acid. The sulfuric acid irritates the nerve endings in the eyes, making them sting.
The release of gas can thus best be prevented by cutting the onions under running tap water or completely under water. This is not very practical of course. For more tips and information, please check links in External links section.
Different species of onions will release different amounts of sulfenic acids, thus some will cause more tear formation than others.
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 garlic chives. There are also species such as Allium moly which are grown for ornament.
Several species of wild onion, including A. canadense and A. diabolense, can be collected in the wild and their leaves and bulbs used as food.
Why do onions make you cry?
Related species
allium cepa
External links
References