Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: neilep on 02/09/2007 21:29:02

Title: Why does cooking onions make them sweet ?
Post by: neilep on 02/09/2007 21:29:02

Here's a recipe for you, but it takes some time to do it properly !

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Take a few onions and chop em up.....fry them  in butter until they become translucent and then turn the heat down......now comes the long part...if you leave them but stir them occasionally they will eventually  (can take a good couple of hours on a low heat) become the most sweetest of oniony chutneys.

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They will be dramatically reduced to something like a fifth of their original volume. There is a short cut where you keep the heat relatively high....stir often and add some sugar/honey or even apricot jam.....but don't burn them !

Great served with cold meat or in a cheese sandwich..it really is quite intense..
........take a chomp out of a raw onion and it's eye watering  joy !!...........but cook em...and they become sweet !!...

.......the question is .....where does the sweetness come from ?....

Title: Why does cooking onions make them sweet ?
Post by: Negin -(Universe) on 04/09/2007 21:29:25

my first guess would be the heat denaturing the enzyme that causes the hot taste and its eye watering property. but I would appreciate it if someone could explain the science behind it properly???

Title: Why does cooking onions make them sweet ?
Post by: _Stefan_ on 05/09/2007 03:52:02

Well plants are full of carbohydrates and perhaps cooking the onion changes those carbohydrates into  molecules that we can taste as being sweet.

Title: Why does cooking onions make them sweet ?
Post by: neilep on 05/09/2007 14:53:37

Quote from: Negin -(Universe) on 04/09/2007 21:29:25

my first guess would be the heat denaturing the enzyme that causes the hot taste and its eye watering property. but I would appreciate it if someone could explain the science behind it properly???

THANK YOU Negin -(Universe),

I appreciates your comment...I too would like to know the sciencetoo.... which leads me to my next post.........

Title: Why does cooking onions make them sweet ?
Post by: neilep on 05/09/2007 14:56:00

Quote from: _Stefan_ on 05/09/2007 03:52:02

Well plants are full of carbohydrates and perhaps cooking the onion changes those carbohydrates into  molecules that we can taste as being sweet.

THANK YOU _Stefan_............this is interesting.

Perhaps the cooking as you say changes the carbohydrates into a palatable form or I wonder if it's the destruction of the sourness that allows the sweetness to become dominant ?

Title: Why does cooking onions make them sweet ?
Post by: Karen W. on 05/09/2007 14:57:03

Thanks for the recipe although I do not know the answer to your question!

Title: Why does cooking onions make them sweet ?
Post by: rosalind dna on 20/12/2007 12:28:43

Neil,
I bought some French pink onions recently and they are sweet also the
juices that in other onions make me "cry". Well these onions don't do that
but they cook faster and get more translucent, when I cook them in butter or oil.

Good recipe which I may use some day. Thanks

Title: Why does cooking onions make them sweet ?
Post by: Karen W. on 20/12/2007 13:39:34

Yeah I have had onions similar to that. Nice eh.. We have some called Walla Walla Sweet Onions, nice red/pink skin with red bleeding into the meat of the onion... They are my favorite sliced on a big burger with cheese and a Tomato! Yummmmmmmm! They are also my favorite in stuffings .. almost anytime.. and they add good color!

Title: Why does cooking onions make them sweet ?
Post by: opus on 20/12/2007 18:17:38

I think it's cos in onions the carbs are stored as starch (complex unsweet carbs) which are broken down into more simple carbs -sweet sugars during the chemical change of cooking. Heston Blumental could give you a more precise answer!

Title: Why does cooking onions make them sweet ?
Post by: TXCraig1 on 06/03/2010 08:10:21

Onions contain a lot of fructans (fructans are fructose polymers - as opposed to starch which is a glucose polymer). Cooking them hydrolizes the polymers, breaking them down into fructose and fructooligosaccharides. It takes a long time for complete conversion resulting in about 80% fructose which is 70% "sweeter" than sucrose. It is the same process that turns the agave heads into fermentable sugars - that takes 24 hours+