Why Are Onions Sweet When Cooked ? Here’s What We Know

If you’ve ever sauteed an onion in your life, you know that the longer you cook it, the sweeter it gets. And when you’re cooking something that calls for a lot of onions, like the Hungarian goulash, it turns the entire dish definitely sweet. The more onions you ad, the sweeter they get.

But why is that ? Why do onions get so sweet when they’re cooked ? After all, if you’re not looking for sweetness this can completely ruin your dish. No worries, we’ll take a look at why onions sweeten when cooked, and how to take out the sweetness.

onion sweet

Why are onions sweet when cooked ?

Onions contain a good amount of sugar, 4.2 grams for 100 grams of raw onion. When cooking we usually use more than 100 grams of onion, and this in turn releases more sugar into our dish.

What happens as the chopped onion cooks, is that the sugar slowly melt and get caramelized. Especially if the moisture level in the pan gets low, and the onions start to get golden-brown.

If you’re thinking the onion doesn’t have that much sugar, know that 100 grams of tomatoes have 2.6 grams of sugar, while sweet potatoes have 4.2 gr of sugar, just like onions.

Those sugars only come out once the onions are cooked for a long time, on low. Or you cook a large amount of onions in one pan. There’s a reason onion jam exists !

Do onions turn to sugar when cooked ?

No, the onions themselves don’t turn to sugar but their sugar does get caramelized. If you’ve ever made caramelized onions you know they turn a wonderful shade of brown and get sticky.

That’s just the sugars developing and turning into caramel, but the rest of the onion is still there. The taste and smell will be much different from just sauteed onions, that’s for sure.

Read also: Are Onions And Garlic Related ? 

What onions are the sweetest ?

Yellow onions, white onions, and sweet onions are the sweetest of the bunch. Of those three, sweet onions are the absolute sweetest and you can easily get them by mistake when reaching for yellow onion.

The only differences between yellow and sweet onions is that the yellow are slightly more golden, with the flesh and off-white. The sweet onions are completely white inside, and have a thinner, more papery outer skin.

That being said, all onions will sweeten and caramelize very well, you can use any you like. As long as you cook then low and slow, they will get there,

Caramelized vs sauteed onions

There’s a bit difference between sauteed and caramelized onions, with the caramelized being obviously sweeter. But you cook them differently too.

Sauteed onions are done on medium heat, with a relatively short cooking time (approx. 10 minutes). They’re the ones that are glassy-looking, just starting to soften, and you stop cooking those once you see some edges start to turn a hint of brown. That’s when you add the rest of the ingredients or the water or continue the cooking process.

Caramelized onions are made using low heat, and have a long cook time, sometimes up to an hour. It depends on how many onions you have in the pan, and how crowded the pan is. More onions in a thick layer mean longer cook time.

When caramelizing onions you have to be very, very patient and get those onions soft and brown. Do not add any sugar to this mixture. Despite the name, there is no added sugar so don’t go adding sugar to these onions. We know the name is caramelized onions, but we need to draw out the sugar in the onion, not add extra.

Should you cover the pan when caramelizing onions ?

Yes, when you’re just starting out and the onions are still raw, cover the pan and let them sweat on low. The point here is to let the onions cook both in the steam and the oil or fat. This will draw the sugar out even better, leading to a very well made caramelized onion.

Of course, you can leave the lid on for the rest of the cooking time and just stir occasionally. If the onions are sticking to the pot, add a tablespoon of water to release the fond on the bottom of the pan. That’s called deglazing and it’s very useful.

How do you take the sweetness out of onions ?

The best way to counter the sweetness of an onion is to add some acidity. This means a bit of vinegar or lemon juice, and maybe an extra pinch of salt if your recipe can allow for it. Extra herbs or mild spices can help too.

Don’t go overboard with the vinegar or lemon juice, it can’t cancel all of the sweetness. But is can cover up a part of it. If you’ve got any other food curiosities be sure to check the related articles below, we’re always adding more food facts to make your life that much easier.