How to Caramelize Onions

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Learn how to caramelize onions so you can elevate your favorite meals. The variety, cutting technique, and cooking method all impact taste.

How to caramelize onions for a sweet and savory flavor that will elevate any dish.

Onions are an essential kitchen staple. We chop or slice them to add earthy, allium flavor to sauces, stir-fries, soups, and stews, or eat them raw in salsas and burgers. But to take their taste to the next level, combine them with a few simple ingredients to experience the caramelization transformation.

With minimal ingredients in the recipe, this makes onion selection, cutting, and how it’s cooked critical to the final color, taste, and texture. You’ll also need a little attention and time to maximize their flavor potential. Luckily, the process for how to make caramelized onions is easy to do. It’s an excellent skill to master to enjoy gourmet meals at home.

The best onions to caramelize

Ingredients and sliced onions in bowls.

There are many different types of onions to choose from. The good news is you can use any kind. When cooked, aromatic varieties like yellow and red onions or shallots give a more complex flavor and profound sweetness. Generally, I recommend grabbing yellow onions to caramelize. They have less water and more sulfur compounds, creating dimension.

Mild and sweet onions like Vidalia, walla walla, Maui, Spanish, or white are higher in moisture and sugar but lower in sulfur compounds. There will be a pronounced sweetness when cooked, but they won’t be as balanced with savory flavor. If experimenting, try combining onions for the best of both worlds.

Caramelization vs. browning

Onions are from the allium family, known for their sulfurous, pungent taste. About 4% of their mass are natural sugars, and if cooked long enough, the glucose, fructose, and sucrose create sweetness. Onions also contain about 1% protein, which, when heated, causes two reactions to occur; caramelization and Maillard browning.

Caramelization occurs when the sugars are exposed to temperatures of 300ºF (149ºC) and above, breaking down into hundreds of flavor molecules and sweet-smelling aromas.

Maillard browning occurs when amino acids break down and react with the sugars in the onion. When the surface reaches 300ºF (149ºC), a deep brown color and meaty, roasted, nutty smell emerge.

Prepare the onions

How wide you slice can help balance the impact on texture to prevent mushy onions. Cut between ⅛ to ¼-inch thick pieces. Any thinner, and they’ll burn or get mushy. For dishes like French onion soup, I prefer to slice onions horizontally so that they melt in your mouth.

Finely cut, onions will be more complex in flavor as more enzymes are released. This is great for toppings or adding to dips.

How cutting impacts taste

Depending on their use, carmelized onions are typically sliced, diced, or minced. Did you know that how you cut an onion significantly impacts the flavor and texture? When onions are cut lengthwise, from the root to the stem end, minor damage is done to the cell walls, creating a milder taste with a sturdier structure.

When sliced horizontally against the grain, more sulfurous flavor compounds produce, intensifying the taste. It also makes for softer pieces when cooked.

Pan selection

Use a wide, heavy-bottomed pan that evenly retains heat, like stainless steel, cast iron, or a Dutch oven. You want a wide surface area, giving the onions plenty of contact with the bottom of the pan. Saute pans and skillets with higher, vertical sides work well too. The more onions, the wider the pan for efficient cooking.

Fat selection

I use two types; butter and vegetable oil. Butter contains milk solids that turn brown and nutty in flavor, sticking to the surface of the onions and jump-starting color change. But the smoke point is lower, causing some concern for burning if not watched, especially with longer cooking times.

For insurance, add equal parts of a higher smoke point fat like olive oil, avocado oil, or other neutral-tasting oil. Ghee is an excellent solution for milky flavors without solids or clarified butter. If you like, you can use one cooking oil.

Heat the fats and season

Adding salt into a dutch oven with butter and oil.

Add some fat to the pan to kickstart the dry-heat cooking process. You want just enough to coat the sliced onions but not so much that they fry to a crisp. Once the butter melts, add in the onions. You don’t want the milk solids to burn. Just brown over time for a butterscotch taste.

Salt promotes the moisture in the onions to move from the interior to the surface. Once the water from the cell walls evaporates, the vegetable will soften so it can begin to caramelize properly. A bonus is the onions get seasoned throughout to balance and enhance the sweetness.

Adjust the cooking temperature

Stirring sliced onions in a pan with a wooden spoon.

Raw onions are crisp and contain a lot of moisture. To reduce the volume and soften the fibers, cook them briefly for 5 minutes over moderate heat. You’ll notice that the surface will just begin to brown.

Now reduce the heat to medium-low to gently caramelize. Do not use high heat; the onions will burn or cook too fast on the surface and not fully soften the centers.

Stir and scrape

Slices of onions in a pan turning light brown.

Once the onions have lost some moisture, the caramelization process can begin. Cook, stirring the pan, then flatten everything into an even layer every few minutes. The natural sugars and juices will start to dry onto the bottom, creating a brown glaze called fond

This process adds color and flavor to the onions. To incorporate it, make sure to scrape continuously, preventing burning. It’s easiest to use a wooden spoon to lift off the fond. Deglazing is an integral part of the process, explained more below. It will take about 35 to 55 minutes, depending on desired taste.

Deglaze the pan

To avoid a burnt flavor on the onions, you must deglaze the pan when you can’t scrape the fond from the bottom. Reduce the heat to medium-low after the first 10 minutes. Make a well in the center of the onions and add the water. Quickly scrape the brown bits of fond. 

The extra moisture will dissolve the browned layer, making it easier to coat. Add 2 tablespoons add a time, about every 5 minutes. Repeat this process and cook the onions until you achieve the desired taste.

The level of caramelization will determine the stopping point

  • Blonde Color: Strong sweetness with a balanced savory taste. There should be no strong sulfurous note or crispness. About 30 to 35 minutes of cooking. 
  • Golden Brown Color: Balanced sweet and savory taste, more robust meaty flavor. Soft in texture. About 40 to 45 minutes of cooking. 
  • Deep Brown: Robust savory, meaty taste, lingering sweetness. Very soft texture. About 50 to 55 minutes of cooking.

Ways to use caramelized onions

  • In an appetizer like French onion dip or hummus
  • On top of a juicy burger, patty melt, or cheesesteak
  • In a meatloaf for a sweeter taste
  • On top of a pizza or stirred into pasta
  • With sliced prime rib to make a sandwich
  • In a quiche or frittata, with or without the crust
  • Stir into an omelet

Frequently asked questions

Do you cover the pan when caramelizing onions?

It’s not required to cover the pan. However, it can be used during the initial stages of cooking. The moisture in the onions steams, softening them slightly faster. Make sure to check and stir every few minutes. You will need to uncover the pan to evaporate the moisture and allow the onions to brown and caramelize.

What’s the difference between caramelized onions and sauteed onions?

Caramelized onion recipes cook the alliums for an extended period to develop a sweet and savory taste and soft texture. Sauteed onions cook briefly to retain a crisp-tender texture and lightly browned surface.

Do you use water to caramelize onions?

Yes! Water or another type of flavorful liquid like stock or broth is added. As the onions release moisture, the sugars move to the surface and caramelize. Water is needed to deglaze the fond inside the pan that could burn.

Close up of wooden spoon scooping up caramelized onions.

Recipe Science

Using baking soda to caramelize onions

Baking soda adds an instant sweetness boost without using sugar. It breaks down the soluble prebiotic fiber called inulin, a polysaccharide, into sweeter-tasting fructose. Use ⅛ teaspoon of baking soda mixed with 1 tablespoon of cold water per 2 to 3 pounds of onions. Stir it in at the end of cooking for about 1 minute. Adding it too early will break down the onion fibers, turning them into mush.

Caramelized Onions

Learn how to caramelize onions so you can elevate your favorite meals. The variety, cutting technique, and cooking method all impact taste.
5 from 3 votes
Prep Time10 minutes
Cook Time30 minutes
Total Time40 minutes
Servings 8 servings
Course Condiment
Cuisine American

Ingredients 
 

  • 2 pounds yellow onions
  • 1 tablespoon unsalted butter
  • 1 tablespoon olive oil
  • ½ teaspoon kosher salt
  • ¾ cup water, plus more as needed

Instructions 

  • Prepare the Onions – Use a sharp knife to trim ½-inch from the stem end and ¼-inch off the root end. Cut in half lengthwise with the stem-side down, then peel. Slice each half from root to stem into ¼-inch thick pieces.
  • Melt the Butter – Set a large, wide pan with high sides or a Dutch oven over medium-low heat. Add the butter, olive oil, and salt, and quickly stir to combine. Do not let the butter brown.
  • Soften the Onions – Immediately add in the onions and stir to coat. Increase the heat to medium. Using a wooden spoon, frequently stir until they begin to soften, 5 minutes. Reduce the heat to medium-low.
    Spread the onions into an even layer. After a few minutes, stir and scrape any browned areas on the bottom of the pan. Repeat this process every few minutes, for 10 minutes. Adjust the heat down if needed to prevent burning.
  • Deglaze and Caramelize – Make a well in the center of the pan. Add 2 tablespoons of water and scrape to dissolve any browned bits (fond) on the bottom. Spread the onions in an even layer. Stir and scrape every few minutes. As more brown fond forms, add 2 tablespoons of water every 5 minutes.
    Repeat the deglazing, stirring, and spreading process until soft and caramelized. Add as much water as needed to deglaze and cook. About 35 minutes for blonde, 45 minutes for golden brown, and 55 minutes for deep brown onions.

Recipe Video

YouTube video

Notes

  • Recipe Yield: About 1 cup
  • Serving Size: About 2 tablespoons
  • Onion Selection: Yellow, sweet onions, red onions, or shallots can be caramelized. Use a mixture for more depth of flavor.
  • Cutting: Onions sliced lengthwise will hold their shape better and have a milder taste. Sliced crosswise, it will be a softer texture and more pungent taste (often used for French onion soup). 
  • Water Substitute: Unsalted vegetable or chicken stock or broth can be added for a savory flavor. Wines like white or red can be used for a fermented taste with light acidity.
  • Storing: Cool completely and store in an airtight container for up to 7 days. Freeze in a resealable plastic bag for up to 6 months. Defrost before using.

Nutrition Facts

Serves: 8 servings
Calories 73kcal (4%)Carbohydrates 11g (4%)Protein 1g (2%)Fat 3g (5%)Saturated Fat 1g (5%)Polyunsaturated Fat 1gMonounsaturated Fat 2gTrans Fat 1gCholesterol 4mg (1%)Sodium 151mg (6%)Potassium 166mg (5%)Fiber 2g (8%)Sugar 5g (6%)Vitamin A 46IU (1%)Vitamin C 8mg (10%)Calcium 27mg (3%)Iron 1mg (6%)

Percent Daily Values are based on a 2000-calorie diet. All nutritional information is based on estimated third-party calculations. Each recipe and nutritional value will vary depending on the brands you use, measuring methods, and portion sizes per household.

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Jessica Gavin

I'm a culinary school graduate, cookbook author, and a mom who loves croissants! My passion is creating recipes and sharing the science behind cooking to help you gain confidence in the kitchen.

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  1. Maria T. says

    This is not the first time I’ve carmelized onions. This is the first time I tried this technique. Up until today I’ve always used, olive oil and a wee bit of sugar cooking low and slow with several larger additions of water. Now I know I don’t need the sugar. The onions were tender and pefectly sweet, though not overly sweet. They tasted like carmelized onions, not onions carmelized with sugar. Much better and worth the time.

    • Jessica Gavin says

      I’m so happy that you gave the caramelization method a try! I have used sugar to help speed up the process, but you don’t have to use it so it’s a nice option.