When I think of raw onion, I think of a punch of concentrated, peppery flavor. I think of watering eyes and harsh sulfur compounds. I think cold, crisp, crunchy and pungent. Caramelized onions are a whole other ballgame.
Caramelized onions are sweet and buttery, soft and kind of slippery. They are mellow and full of deep, rich, sweet flavor—slightly nutty and the perfect accompaniment to a steak or a goat cheese pizza. What kitchen alchemy is it that can turn a pungent raw onion into a sweet and melting treat?
Obviously, caramelized onions are brown. In cooking, browning takes place in several ways. One way is through caramelization, the process by which sugars react with sugars in the presence of high heat.
Another way is through the Maillard reactions. Named for the chemist who first studied these reactions in 1912, the Maillard reactions, of which there are many, are a series of browning reactions that occur when certain sugars react with the amino acids found in proteins. These reactions are accelerated by heat and also the pH of the food being cooked.
Needless to say, a scientific explanation of these reactions is pretty exhaustive and exhausting. As cooks, what we need to understand is that a brown color and a more complex flavor are generally the end result of these reactions. We can use caramelization and the Maillard reactions to produce beautifully browned, deeply flavored foods, even if we do not understand the precise chemistry by which it all occurs.
While onions are made up mostly of carbohydrates in the form of fiber and sugar, they do contain a small amount of protein. Knowing this tells us that browning will occur through both caramelization (sugars reacting with sugars) and Maillard reactions (sugars reacting with amino acids).
How to Caramelize Onions
Caramelized onions are quite easy to make. Other than time and an onion, there is not much needed to produce wonderful, deeply caramelized onions. Because of the way onion cells are lined up, how you slice up the onion will have an effect on the final product.
If you want caramelized onions that almost melt in the mouth, you will want to cut thin slices longitudinally, or from the root end to the stem end. If you’d like your caramelized onion to have a little more structure and not break down so much, slice them into thin rings across the equator. If you would like smaller caramelized pieces, you can also chop or dice the onions.
1 large onion, sliced per your preference 2 tablespoons olive oil, butter, or a mixture of the two Heavy pinch of salt Optional additions for extra flavor Freshly ground black pepper Fresh minced herbs, or dried herbs A teaspoon of honey, agave nectar or corn syrup
How to Caramelize Onions at Home
Heat a large sauté pan over medium-low heat. Add the oil/butter.
Once the butter has melted and is hot, add as many onions to the pan as will fit in a 1/2” layer in the pan. Sprinkle the salt over the onions. The salt helps to draw water and dissolved sugars out of the onion’s cells. When you salt the onions at the beginning, it will take longer to achieve browning because of the extra water it draws out, but ultimately, your onions will have a much better flavor and will brown more evenly if you add the salt at the beginning of the cooking process.
Cook the onions over medium low heat. Cooking the onions at a relatively low temperature, called sweating, allows all the water to release into the pan and then evaporate slowly. Sweating also ensures that your onions will be soft and caramelized all the way through, and not just on the outside.
Stir the onions every couple of minutes, and adjust the heat so you here just the merest sizzle. If your pan would not hold all of the onions, add more as the ones in the pan cook down and free up more room in the pan.
Add in your optional ingredients, if you choose to use them, and continue cooking on medium-low to low heat, stirring frequently, until the onions are soft and anywhere from honey-colored to deep brown, depending on how caramelized you want them to be.
The process can take anywhere from ten to fifteen minutes to upwards of half an hour, depending on how many onions you are cooking and your preferred level of caramelization. Don’t worry; as long as you cook them slowly and stir them frequently, you will not end up with burned onions.
Other vegetables related to onions (the Allium family) also respond beautifully to caramelization. Try caramelizing leeks, shallots or even garlic.