Learn how to caramelize onions to elevate your favorite meals. The variety, cutting technique, and cooking method all impact taste.
Recipe Science
- To prevent mushy onions, slice them from root to stem between ⅛ to ¼-inch thick. Thinner slices may burn or soften too much.
- Onions contain about 1% protein, contributing to caramelization and Maillard browning when heated, enhancing flavor complexity.
- Caramelization starts as onions lose moisture, forming a brown fond at the pan’s bottom. Deglazing is key to preventing burning.
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Featured Comment 4
“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 perfectly sweet, though not overly sweet. Much better and worth the time.”—Maria
Why It Works
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, onion selection, cutting, and cooking are 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 of making caramelized onions is easy. It’s an excellent skill to master to enjoy gourmet meals at home.
Ingredients You’ll Need
Onions: 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.
Fat: I use two types; butter and olive oil. Butter contains milk solids that turn brown and nutty in flavor, sticking to the surface of the onions and jump-starting color change. 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 fruity olive oil.
Salt: Salt promotes the moisture in the onions to move from the interior to the surface. Once the water from the cell walls evaporates, the vegetables will soften so it can begin to caramelize properly. A bonus is the onions get seasoned throughout to balance and enhance the sweetness.
Water: During deglazing, added moisture dissolves and lifts sugars and juices from the pan’s bottom. Scraping the pan incorporates the fond (browned bits) with the onions, enhancing their flavor with deeper, richer notes.
See the recipe card below for all ingredients and measurements (US and metric).
Ingredient Substitutions
- Onion Options: Mild and sweet onions like Vidalia, walla walla, Maui, Spanish, or white are higher in moisture and sugar but lower in sulfur compounds. They will be pronouncedly sweet when cooked, but their savory flavor will be less balanced. If you’re experimenting, try combining sweet onions and savory yellow onions for the best of both worlds.
- Fat Swaps:Ghee is an excellent solution for milky flavors without solids or clarified butter. Use a neutral-tasting oil like olive oil or avocado oil. If you like, you can use one cooking oil.
- Salt Substitutes: Use sea salt or half the amount of table salt since the granules are much finer.
- Liquid: Add a dry white wine for a fermented note. Add vegetable or chicken stock or broth for a more savory taste. Add a splash of apple cider vinegar or balsamic vinegar for tanginess.
- Sugar: A small amount of granulated sugar or brown sugar will accelerate caramelization. However, deglaze earlier and reduce the heat as needed to prevent burning. Add ½ to 1 teaspoon of sugar per pound of onions.
How to Make Caramelized Onions
Step 1: Prepare the Onions
Cut them from root to stem 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.
Pro Tip: Check out my tutorial on how to cut an onion. How wide you slice them can affect the texture. Finely cut onions will be more complex in flavor as more enzymes are released. This is great for toppings or using for French onion dip.
Step 2: Melt the Butter
Add the butter, olive oil, and salt 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. You don’t want the milk solids to burn. Just brown over time for a butterscotch taste.
Pro Tip: 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.
Step 3: Soften the Onions
Once the butter melts, add the onions. Cook them briefly for 5 minutes, stirring occasionally, over moderate heat to reduce the volume and soften the fibers. The surface will just begin to brown.
Reduce the heat to medium-low; do not use high heat, or the onions will burn or cook too fast on the surface and not fully soften the centers. 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 reduce to the bottom of the pan and dry, 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.
Step 4: Deglaze and Caramelize
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 continue to cook the onions until you achieve the desired taste. The process takes about 35 to 55 minutes. See below for stopping points.
The Level of Caramelization Will Determine the Stopping Point:
- Blonde Color: It should have a strong sweetness and a balanced savory taste. There should be no strong sulfurous note or crispness. It should take about 30 to 35 minutes to cook.
- Golden Brown Color: Balanced sweet and savory taste, more robust meaty flavor. Soft in texture. About 40 to 45 minutes of cooking.
- Deep Brown: It has a robust savory taste and lingering sweetness. It has a very soft texture. It takes about 50 to 55 minutes to cook.
Ingredient Chemistry: 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.
Frequently Asked Questions
Depending on their use, caramelized 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.
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, which could burn.
Covering the pan is not required. 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.
In caramelized onion recipes, the alliums are cooked for an extended period to develop a sweet and savory taste and soft texture. Sauteed onions are cooked briefly to retain a crisp-tender texture and lightly browned surface.
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.
To caramelize onions, cook them for about 15 minutes to reduce volume and soften texture, starting caramelization as moisture leaves the cells. Deglazing is crucial to prevent burning and enhance flavor. The entire process takes 35 to 55 minutes, depending on the desired taste indicated by color: blonde for strong sweetness and balanced savory notes, golden brown for a robust, meaty flavor with balanced sweetness, and deep brown for an intense savory and meaty taste with a lingering sweetness.
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.
Serve This With
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Caramelized Onions
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
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, they will have a softer texture and a 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
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.
Dave says
Aside from adding water, this is how I do these. Yes, it is time consuming but so worth the wait. Start with about 3X as many onions as you think you’ll need. They really cook down.
However, I was really fascinated by the flavor changes depending on how it’s sliced and that they can be frozen. Interesting.
Further, I love your food science tips. Thanks for those.
Jessica Gavin says
You’re welcome, Dave!
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.