Knowing how to caramelize onions is a great skill to have in your home cooking arsenal. It takes some time (and patience) but it will reward you with sweet, rich, savory, flavorful onions that will improve the taste of any dish! Use them to make French onion soup or you can add them to sauces, chicken dishes, or burgers.
What are caramelized onions?
Caramelized onions are onions that are sliced/diced and cooked long enough to caramelize the sugars that naturally occur in onions. They are light brown in color, very sweet, and have a deep savory flavor.
What does caramelized mean? Caramelization is a chemical process of breaking down sugar and transforming it into caramel that gives it a delicious sweet nutty flavor and golden color. The caramelization of onions is the same process as caramelizing sugar (making caramel) where the natural sugars in onions are being caramelized.
You only need 3 ingredients to make caramelized onions:
- Onions – you can caramelize any type of onions. I usually use yellow onions which are most versatile.
- Salt – is optional but it helps to soften onions more quickly.
- Fat – to cook the onions. I like to use clarified butter if I have it on hand. If not, I will use half regular butter and half olive oil or just olive oil. I don’t like to use just butter – it burns quickly so you need to pay attention more to not burn the onions. Clarified butter is a type of butter that is suitable for frying and still has this amazing buttery flavor. It’s very easy to make at home.
How to caramelize onions
Peel the onions, cut them in half, and then into 1/4-inch (7mm) slices. The slices should be uniformly thick – they will cook evenly. Don’t make the slices too thin – they will burn too quickly, I also don’t like to cut very thick slices – I think the 1/4-inch thick slices are most pleasant to eat. You can also dice the onions.
Heat the clarified butter or butter/olive oil in a large, heavy-bottomed pot over medium/medium-high heat.
You can caramelize onions in every pan or pot but a heavy-bottomed pot ensures that the onions don’t burn too quickly.
When the butter/olive oil is hot, add the onions and 1 teaspoon of salt.
Cook the onions stirring them occasionally. They will now begin to soften and will look like sauteed onions (the photo above shows onions that have been cooked for 15 minutes).
At the beginning you can stir the onions from time to time but as they darken you will need to stir them more often. While stirring make sure to scrape all the brown bits on the bottom of the pot (this is called fond). Be careful not to burn the onions – they will be bitter. Anytime the onions look like they are starting to burn on the bottom of the pot – stir them with a spatula or deglaze the pot with a small amount of water.
The heat will depend on the stovetop and from my experience it can vary greatly, so you need to use your judgment here. Start cooking the onions on medium or medium-high (to evaporate excess liquid from the onions), then reduce to medium/medium-low, then cook the onions on low at the end of the cooking time. Adjust the heat to lower if you see that the onions are browning too fast, and increase the heat if you see that the onions are cooking/browning too slow.
The onions on the photo above have been cooked for 30 minutes.
Caramelizing onions can not be speeded up (without sacrificing their flavor or texture) – they are not onions that have been cooked over high heat and browned. They really need time for natural sugars to caramelize and develop an amazing, deep flavor. On the other hand, you can not caramelize onions for too long – they will be bitter.
You need to cook the onions for 45-60 minutes – they will be soft and light brown in color.
The onions are done and ready to use in any recipe that calls for caramelized onions! (photo above).
Deglazing the onions
Now you can deglaze onions, which means you can add some liquid to the onions to make them more saucy and add additional flavor.
Preferably it should be something slightly sour to balance the sweetness of onions – I usually use dry white wine (for French onion soup) or balsamic vinegar when using caramelized onions as a topping for steak or burgers.
What can you use to deglaze caramelized onions:
- dry white wine
- dry red wine
- sherry vinegar
- balsamic vinegar
- port wine or Marsala wine
- dry vermouth
- chicken or beef broth
You can keep caramelized onions for up to 3-4 days in the fridge. They also freeze very well – it’s good to make a big batch and freeze some since caramelizing onions is quite time-consuming. You can freeze the onions for about 3 months (for up to 6 months).
How to use caramelized onions
- French onion soup
- Mushroom quesadilla with caramelized onions
- Puff pastry onion tart with pear and onions (this recipe uses partially-caramelized onions that are finished in the oven)
- French onion dip
- Add them to sauces (for example creamy sauce or mushroom sauce), you chop the onions and freeze it in ice cubes and add a small amount of caramelized onions to gravy or meat sauces.
- French onion meatballs (the recipe is coming soon)
- As a topping for steak, sandwiches (like grilled cheese sandwich), or burgers.
- Make brie/goat cheese and caramelized onions toasted baguette slices.
It takes 45-60 minutes for onions to caramelize. The cooking time will depend on how thinly you sliced the onions, the amount of onions, the size of the pot, the type of the pot, and the heat of your stove.
It’s better to use both butter and oil or use just clarified butter.
No, you don’t need sugar to caramelize onions although it speeds up the process a bit. Onions naturally contain sugar that caramelizes during the caramelization process.
Salting the onions makes them soften more quickly so you should add some salt at the beginning of the cooking time. If you have not added any salt at the beginning, lightly salt caramelized onions at the end.
Sporadically at the beginning and very often at the end of the cooking time. It will also depend on the heat under the pot.
They are light brown/golden in color, very sweet, and soft/jammy. It will take at least 45 minutes.
Sauteing the onions takes a shorter amount of cooking time, about 5-10 minutes. The onions are just slightly soft and sweet. Caramelized onions are onions that are cooked for a longer period of time, at least 45 minutes which allows the natural sugar in onions to brown and caramelize. These onions are very soft/jammy, very sweet, and have a deep complex flavor.
The best pot/pan for caramelizing onions is cast iron or stainless steel. It should be a heavy-bottomed pot/pan. Non-stick pans and enameled cast iron are known for slowing down the caramelization process (the onions don’t stick to the surface and don’t brown easily). Dutch oven (enameled cast iron) cooks the onions a little bit slower but thanks to a thick bottom the pot is evenly heated and onions don’t burn so quickly so you can just increase the heat and cook the onions in the same amount of time as in not-coated cast iron/stainless steel.
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How To Caramelize Onions
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- 2 tablespoons butter
- 2 tablespoons olive oil
- 3 lbs (1.4kg) yellow onions
- 1 teaspoon salt
- Peel the onions, cut them in half, then into 1/4-inch (7mm) slices (you can also dice the onions).
- Heat butter and olive oil in a large, heavy-bottomed pot. When hot, add the onions and 1 teaspoon of salt.
- Cook the onions for about 45-50 minutes until caramelized – they will be soft and light brown/golden in color.
- At the beginning you can stir the onions only from time to time but as they darken you will need to stir more often. While stirring make sure to scrape all the brown bits on the bottom of the pot. Be careful not to burn the onions – they will be bitter. Anytime the onions look like they are starting to burn on the bottom of the pot – stir them with a spatula or deglaze the pot with a small amount of water.
- The heat will depend on the stovetop and it can vary. Start cooking the onions on medium or medium-high heat (to evaporate excess liquid from the onions), then reduce to medium/medium-low, then cook the onions on low at the end of the cooking time. Adjust the heat to lower if you see that the onions are browning too fast, and increase the heat if you see that the onions are cooking/browning too slow.
- You can caramelize any type of onion.
- You can use clarified butter or just olive oil to cook the onions. I don’t recommend using just butter because it burns too quickly.
- Caramelizing onions can not be speeded up (without sacrificing their flavor or texture) – they are not onions that have been cooked over high heat and browned. They really need time for natural sugars to caramelize and develop an amazing, deep flavor. On the other hand, you can not caramelize onions for too long – they will be bitter. The caramelization process takes at least 45 minutes for up to 60-70 minutes.
- Calories = whole recipe. This is only an estimate!