How can you cut an onion without crying?
In order to prevent crying, it helps to understand why it happens. There is a chemical reaction that occurs when you cut an onion; you damage the onion's cells and the enzyme (Syn-ropanethial-S-oxide) that escapes acts as a lachrymatory agent. When that agent hits your eyes, it mixes with your tears to make sulfuric acid, and your tear ducts activate in an attempt to wash out the contamination.
The sharper your knife, the less likely you are to cry when you chop an onion. A dull knife will actually smash the onion rather than slice it cleanly, so the onion lets out more of the compound that irritates the eyes. Use a good chef's knife and break out your knife sharpener regularly to sharpen it up.
Take your pick — you can let your onions chill in the fridge, pop them in the freezer for 15 minutes, or just dunk them in an ice water bath for a little while. Getting an onion nice and cold helps prevent eye irritation by reducing the number of chemicals released through cutting.
Chill or freeze onions to minimize the amount of gas released into the air. Light a match before you peel or slice the onion. The sulfur disables the compounds in onions that make your eyes water.
So, that being said:
- Wearing goggles is the most obvious answer. It may look a little silly, but it's the easiest way to prevent the onion's enzyme from reaching the eyes.
- Sharpening your knife beforehand limits the damage to the onion cells, thus releasing fewer gases.
- Spraying your cutting board with vinegar slows down the chemical reaction. It does, however, make your onions smell/taste like vinegar.
- Always placing the cut side down will minimize the chemicals released into the open air.
- Cutting onions under the kitchen vent will remove some of the chemicals from the air.
- And finally, try not to form an emotional bond with your onion.
When you cut an onion, it releases a gas called, Propanethiol S-oxide. When it is mixed with certain enzymes in the onion, it creates a sulfur gas also.
Both gases then get to your eyes and create a mild acid that irritates the eyes. That why we cry during cutting the onion.
Syn-propanethial-S-oxide gets into the air and comes in contact with our eyes. The lachrymal glands become irritated and produces the tears!
It can be an irritating and even painful process to slice and dice onions, so here are some ideas you can try without getting weepy:
Use a sharp knife to cut the onion—you'll release less of the enzymes into the air.
Cut onions in cold water.
Cut the root last—it has a higher concentration of enzymes.
Chill or freeze onions to minimize the amount of gas released into the air.
Light a match before you peel or slice the onion. The sulfur disables the compounds in onions that make your eyes water.
Use a small manual or electric food chopper or food processor.
Wear kitchen goggles to protect your eyes.
Remember not to touch your eyes when you chop onions. And make sure to wash your hands thoroughly after you're finished. If your eyes are especially irritated, flush them with cool water or a soothing eye rinse. If your symptoms don't disappear within a few hours…..
Onions produce the chemical irritant known as syn-propanediol-S-oxide. It stimulates the eyes' lachrymal glands so they release tears. Scientists used to blame the enzyme alliinase for the instability of substances in a cut onion. Recent studies from Japan, however, proved that lachrymatory-factor synthase, (a previously undiscovered enzyme) is the culprit (Imani et al, 2002).
The process goes as follows:
Lachrymatory-factor synthase is released into the air when we cut an onion.
The synthase enzyme converts the amino acids sulfoxides of the onion into sulfenic acid.
The unstable sulfenic acid rearranges itself into syn-ropanethial-S-oxide
Onions absorb sulfur from the soil. When onions are chopped, certain enzymes are released from its cells that react with sulfur to form amino acid sulfoxides.
These, in turn, create the highly unstable syn-propanethial-S-oxide (a combination of sulfuric acid, sulfur dioxide, and hydrogen sulfide) which is in a gaseous state and is an irritant.
So when this comes in contact with your eyes, it triggers a burning sensation ( through the ciliary nerve).
Tears in the eyes are regulated by the lachrymal gland ( situated just above your eyelids). When the brain gets the message that there is some irritant in your eyes, it kick-starts the lachrymal gland which starts producing tears in order to flush out the irritant.
Why does this not occur in cooked onions? Because in cooked onions, the enzyme required for the formation of irritant (propanethial-S-oxide) is inactivated (enzymes work at optimal temperature and high temperature causes their denaturation).
