How to Caramelize Onions (2024)

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

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

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

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

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

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