When an onion is cut, certain lachrymator compounds are released causing the nerves around the eyes lacrimal glands to become irritated. These compounds consist of methionine and cystine that are part of the amino acid family. Protein is made up of several of these amino acids grouped together.
When an onion is sliced or diced, the onion's cells release these compounds into the air. When this occurs, "enzyme" works to alter the amino acids into lachrymator compounds.
This form of sulfuric acid irritates the nerves around the eyes making them tear. How can we prevent this reaction? Use a sharp knife to cut the onion to reduce the amount of damage to the onion cells. Cool the onion in a refrigerator to suppress the scattering of the lachrymator. Soak the onion in water to dissolve the amino acids. Propanethial S-oxide is a lachrymatory agent, meaning that it generates tears when it touches the eye. Propanethial S-oxide turns into sulfuric acid when it touches the water layer that covers and protects your eyeballs.
But just like onions, your eyes are also equipped with a defense mechanism meant to protect them from harm. When the nerves in each eye detect a lachrymatory agent, they generate tears to flush it out.
Some people are more likely to cry when cutting onions than others. The onions that generate the harshest chemical reaction have lots of sulfur-containing compounds. These include yellow, red, and white onions. Sweeter types, such as green onions , have less sulfur, are less pungent, and produce fewer tears in most people.
Through genetic transformation, crop scientists have also created tear-free onion varieties. While not yet mass-produced, you can find tear-free onions called Sunions in some specialty markets. Here are some tips to reduce crying from onion irritation:. First, keep in mind that the length of time you store onions affects their potency and tear-producing abilities.
Fresher onions are less likely to cause crying than those that have been stored for an extended period of time. However you slice them, try to avoid cutting your onion near the root end. This is the part that contains the highest concentration of sulfuric compounds that can make you cry. Using a sharp knife may also help. The sharper the knife, the less damage is done to the onion, and fewer irritations are released into the air as a result.
To reduce or eliminate onion tears, you may have the best luck if you diminish the sulfuric acid compounds in the onion itself. To do this, try chilling your onion in a bowl of ice water for 30 minutes before cutting. Some people also prefer to cut their onions while submerged in cold water. Try running a fan to circulate the air or wearing eye protection, such as goggles, while you prepare onions.
One old tale says to keep a piece of white bread in your mouth while cutting, based on the theory that the bread will absorb onion vapor. The distinctive taste of fresh onion can be hard to replicate. But you may want to substitute onions in your cooking if they frequently cause uncomfortable, disruptive eye symptoms.
One sulfur compound in onions, called propyl sulfoxide, escapes into the air when you slice an onion. When it comes into contact with moisture, such as water vapor in the air or the natural moisture around your eyes, it changes into sulfuric acid. Sulfuric acid has a strong smell and irritates your eyes, so they make tears to wash it away.
This lets most of the noxious sulfuric compounds, which are found in the root, escape. Then you can remove the pointy tip of the onion, peel its skin and slice it with fewer tears. And gardeners love to grow ornamental alliums — members of the onion family that are bred for their looks. Many are very attractive, with blooms that make balls of color on long straight stalks.
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