A Guide to Making Caramelized Onions, Plus Easy Caramelized Onions Recipe

Caramelized onions are produced when the naturally astringent vegetable is slowly cooked in fat over low heat, triggering the caramelization process and resulting in a delectably soft and sweet end product with a vastly different in texture and flavor from its raw form.

Caramelization is a non-enzymatic browning reaction that takes place during the cooking process as steam is released and the sugars begin to break down in a process called pyrolysis. The result is the development of a deep brown color and rich, nutty flavor with pronounced notes of sweetness.

Thanks to the natural sugars contained in onions, caramelization occurs when this versatile vegetable is exposed to heat. Onions take a particularly long time to caramelize due to their high water content—about 89 percent—which requires a longer sweat time before the sugars begin to break down.

The key to the onion caramelization process is time. Most caramelized onions will take 45 minutes to one hour to cook to golden brown perfection, although there are a few methods for rushing the process.

Note that while these methods will produce softened, browned onions more quickly, they will lack the rich depth of flavor that can only be achieved by a slow and steady caramelization process.

1. High heat. To speed up the low and slow caramelization process, crank up the heat to medium-high or high and cook the onions in butter or olive oil, stirring the vegetables frequently to prevent burning. After about 5 minutes, when the bottom of the onions begin to brown, add a couple of tablespoons of water to deglaze the pan. Scrape the browned bits from the bottom into the onions, repeating this process every couple of minutes for 15 minutes.
2. More sugar. Another option for speeding up the process is to brown the onions in a dry pan, with no salt or fat, for 5 minutes before adding oil and a tablespoon of brown sugar or balsamic vinegar and cooking until fully soft. This will help to quickly develop the sweetness and slight bitterness expected when you caramelize onions.

The best type of pan for caramelizing onions is a wide, thick-bottomed cast iron or stainless steel pan. Although onions can also be caramelized with alternative cooking methods and containers, like a crock pot or slow cooker, nothing beats a sturdy sauté pan. The size of the pan will depend on the quantity of onions being caramelized. To avoid overcrowding, a 12-inch pan should contain no more than 2 large onions at a time. To increase the quantity of onions cooked at once, use a larger skillet.

1. Choose the right onion. When caramelizing, use sweeter varieties of onions with higher quantities of natural sugar, like yellow onions, white onions, and Vidalia. Red onions are not an ideal choice for caramelization because they're less sweet and more astringent.
2. Don’t slice onions too thin. Although caramelized onions should be cut into relatively thin, uniform pieces, slicing them too narrow can result in the onions drying out and burning easily. Shoot for an ⅛-inch thickness across the board.
3. Avoid overcrowding. Onions that are packed too tightly in the pan will produce tons of excess water, which will make the caramelization process move along extremely slowly. To avoid this, cook no more than 2 large onions per 12-inch pan.
4. Customize the fat content. The more fat in the pan during the caramelization process, the more frying that will take place. A thin layer of olive oil or butter will result in onions that fall on the softer side, while a larger quantity of fat will result in a slightly charred final product.
5. Don’t jump the gun. While the sautéed onions might appear decently soft and golden half way through the caramelization process, the development of the rich caramelized flavors takes time and patience. Wait until the onions have turned a deep brown color and are fully soft before removing them from the heat.

Deglazing is an essential part of the caramelized onion process, as lifting the rich browned flavors from the bottom of the pan and mixing them back in with the onions will make them even more flavorful and delicious.

1. To deglaze a pan once the onions have finished cooking, pour a couple of tablespoons of water, red wine, white wine, broth, or balsamic vinegar into the pan.
2. Once the liquid begins to boil, use a wooden spoon or spatula to scrape up the browned bits on the surface of the pan and mix it into the onions.
3. This process can be repeated multiple times during the caramelization process, each time the pan develops a layer of browning.

Although caramelized onions are arguably delicious enough to eat on their own, these flavor-packed vegetables are typically used as a topping for other savory side dishes and main courses. Some great options for pairing with caramelized onions are tarts, dips, omelettes, crostini, pizza, quesadillas, steak, chicken, and the ultimate classic, French onion soup.