# Why do onions taste sweet when cooked?

**URL:** <https://boards.straightdope.com/t/why-do-onions-taste-sweet-when-cooked/190840>\
**Category:** Factual Questions\
**Created:** [July 25, 2003, 11:32am UTC](https://boards.straightdope.com/t/why-do-onions-taste-sweet-when-cooked/190840 "2003-07-25T11:32:39Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![starman](https://avatars.discourse-cdn.com/v4/letter/s/8c91f0/32.png) [@starman](https://boards.straightdope.com/u/starman)\
**Post date:** [July 25, 2003, 11:32am UTC](https://boards.straightdope.com/t/why-do-onions-taste-sweet-when-cooked/190840/1 "2003-07-25T11:32:39Z")

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Why do onions taste sweet when cooked, particularly when cooked for very long periods?  
-Oli

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**Author:** ![curly\_chick](https://avatars.discourse-cdn.com/v4/letter/c/7ba0ec/32.png) [@curly\_chick](https://boards.straightdope.com/u/curly_chick)\
**Post date:** [July 25, 2003, 11:37am UTC](https://boards.straightdope.com/t/why-do-onions-taste-sweet-when-cooked/190840/2 "2003-07-25T11:37:47Z")

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The naturally ocurring sugar gets caramalised by heat and the sweet flavour is magnified by the loss of water.

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**Author:** ![bizzwire](https://avatars.discourse-cdn.com/v4/letter/b/958977/32.png) [@bizzwire](https://boards.straightdope.com/u/bizzwire)\
**Post date:** [July 25, 2003, 11:40am UTC](https://boards.straightdope.com/t/why-do-onions-taste-sweet-when-cooked/190840/3 "2003-07-25T11:40:39Z")

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Chemistry.

Onions contain starch, and starch is basically a long chain of sugar molecules stuck together. Heating causes these chains to break, releasing the individual sugar molecules. The more cooking, the more sugar that’s released.

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**Author:** ![Biig\_Tasty](https://avatars.discourse-cdn.com/v4/letter/b/ecc23a/32.png) [@Biig\_Tasty](https://boards.straightdope.com/u/Biig_Tasty)\
**Post date:** [July 25, 2003, 11:40am UTC](https://boards.straightdope.com/t/why-do-onions-taste-sweet-when-cooked/190840/4 "2003-07-25T11:40:47Z")

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I like them raw

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**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\
**Post date:** [July 25, 2003, 11:41am UTC](https://boards.straightdope.com/t/why-do-onions-taste-sweet-when-cooked/190840/5 "2003-07-25T11:41:55Z")

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Because:  
-The pungent volatile compounds have been broken down or driven off by the heat.  
-The cells have broken open and released their contents.  
-The water content is reduced, concentrating the flavours.  
-The sugars may have partially caramelised, making them more intense in flavour.

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**Author:** ![Amfet](https://avatars.discourse-cdn.com/v4/letter/a/49beb7/32.png) [@Amfet](https://boards.straightdope.com/u/Amfet)\
**Post date:** [July 25, 2003, 12:57pm UTC](https://boards.straightdope.com/t/why-do-onions-taste-sweet-when-cooked/190840/6 "2003-07-25T12:57:03Z")

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Also, the pungent flavor of onion develops after it is cut or chewed due to the action of the enzyme [alliinase](http://www.uga.edu/onion/pdf%20files/Onion%20flavor%20chemistry%20opt.pdf). The heat of cooking probably deactivates this enzyme.

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**Author:** ![Sasssy](https://avatars.discourse-cdn.com/v4/letter/s/73ab20/32.png) [@Sasssy](https://boards.straightdope.com/u/Sasssy)\
**Post date:** [July 25, 2003, 1:15pm UTC](https://boards.straightdope.com/t/why-do-onions-taste-sweet-when-cooked/190840/7 "2003-07-25T13:15:16Z")

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I love sauteed onions. Yum.🙂 I like them raw too (Vidalia are my favorite ones).

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**Author:** ![istara](https://avatars.discourse-cdn.com/v4/letter/i/e79b87/32.png) [@istara](https://boards.straightdope.com/u/istara)\
**Post date:** [July 25, 2003, 10:33pm UTC](https://boards.straightdope.com/t/why-do-onions-taste-sweet-when-cooked/190840/8 "2003-07-25T22:33:41Z")

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They are FULL of sugar compared to many other vegetables. A total nightmare for the Atkins diet, you have to be really careful how much you eat.

Interestingly, after a couple of weeks of strict Atkins Induction (the first stage of the diet) I ate a pretty much raw onion - hard and crunchy. It tasted so sweet to my now sugar-un-desensitised tastebuds it was almost unpleasant.