Why do onions make you cry? 16 comments

20 Nov 2005 @ 11:29, by Silvia Martínez Who has never cried while cutting an onion? (well, apart from those who have never cut one hehehe). This is a little explanation in easy terms. Inside the onion cells there are some chemical compounds which contain sulfur. When you cut an onion its cells are broken and those chemical compounds then undergo a reaction that transforms them into a more volatile sulfured products, which are released into the air. These sulfured compounds react with the moisture in your eyes forming sulfuric acid, which produces a burning sensation. The nerve endings in your eyes are very sensitive and so they pick up on this irritation. The brain reacts by telling your tear ducts to produce more water, to dilute the irritating acid. So you cry to keep your eyes protected from the acid. There are some tricks to make onion-dicing less problematic: - Chop the onion under cold water. The volatile sulfured compounds will be released but then they react with the water, instead of reaching your eyes. - You can freeze the onion for 10 minutes before cutting it. The cold temperature of the onion will slow down the chemical reaction which forms the volatile sulfured compunds. Versión en español aquí.

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Category: Science for everybody 

21 Nov 2005 @ 19:38 by jstarrs : You should publish
a scientific book of easy explantions of weirds things like red tomatoes and onions that make you cry, for kids.
And adults.
My mother used to put a spoon or fork between her lips when she cut onions.
Onions skin is also good for putting on a small wound.
It was also used to color material a bright red.
Or was it yellow?
What's good for the memory?
;0)
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:-)
You're right about the dyes. Yellow onion skins can be used to make golden dyes because they have a pigment named quercitin, which is an antioxidant responsible for the onion colour. Red onions give a cranberry red dye, coming from another chemical component called anthocyanin (present also in the beets).

You can play Chemistry in the kitchen and try to make the dye :-):
- Peel the yellow onions and lay out the skins on a cookie tray to dry in a place with good air circulation.
- Put the skins in a nylon stocking and tie the top shut.
- Boil them in a stockpot with 2 quarts of water for 15 to 20 minutes.
- Remove the stocking and voila!!  

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