I love the taste of lightly fried sliced onion. I've heard this referred to as 'caramelizing' the onion.
Is there sugar in the layers of an onion that is changed to caramel, or is this just a phrase?
My question is: If you 'caramelize' an onion, do they contain sugar?
Yes, onions contain sugar, just like most fruit and vegetables. It is not simply a common phrase, it is true caramelization.
They have 4.24 g of sugar per 100 g in total (wet weight). For dry weight 40% is sugar. See the USDA nutrient database for more details.
Onion does contain sugars when raw, but they are pretty much indigestible and tasteless. Cellulose (vegetable fiber), for example, is a complex carbohydrate which only ruminants can digest with the aid of bacteria in their stomach.
With caramelization, complex sugars in onion split into simpler ones, which are the ones we can taste, by the action of heat. Therefore, fried onion tastes sweeter, and so does tomato, etc.
When sugar cane crops are ready to be harvested, dry leaves are burnt in situ in order to increase the yield of sucrose by the same effect: a fraction of the existing complex sugars are turned into sucrose (saccharose).
The answer is: An onion contains sugar whether you "caramelize" it or not. "Caramelizing" an onion (or anything else) helps to emphasize the natural sweetness of the onion. You're basically cooking off the water in the onion and concentrating the sugars.
Onions are very sugary. People eat so much sugar these days however, that they don't notice. When someone does something like the atkin's diet or similar, they begin to taste how sweet all those veg really are.
