Have you ever wondered why recipes for so many dishes begin with cooking an onion? It’s because there’s no ingredient quite like an onion for adding subtle sweetness and bolstering other flavors at the same time. In fact, the type of onion that’s used, the way it’s cut, and the way it’s cooked all affect the flavor and texture of a finished dish in dramatically different ways. So if you ever set out to create a new dish or if you just want to tinker with an old favorite, pay special attention to the onion.
All onions are not equal
While leeks and scallions can play a delicious role in cooking, globe onions of all kinds—yellow, white, red, sweet—and shallots are more assertive and versatile in cooking.
Yellow onions are all-purpose onions. Since they are inexpensive and readily available, I use them more than any other type. They have the strongest flavor of all the globe onions, so they’re best when cooked. They’re usually my first choice for stocks and broths. Spanish onions are similar to yellow onions, but they’re larger.
White onions retain their firm texture. They’re a bit milder than yellow onions, so they can be eaten raw (in a salsa or on a hamburger), but they’re also strong enough to hold up under heat. I especially love how white onions hold their shape and texture when they’re sautéed.
Think raw when you think of red onions. Though red onions (a.k.a. Bermuda or Italian onions) are also good when they’re simmered into a jam-like relish for meats, their crisp texture and sweet flavor are really at their best when eaten raw. Marinating them briefly in a vinaigrette (or other acidic bath) accentuates their bright purple color.
Sweet onions are regional specialties. Vidalias from Georgia, Mauis from Hawaii, Texas Sweets, and Washington Walla Wallas are all coveted for their sweet flavor. Eat them raw in salads or grill them briefly to highlight their fantastic flavor.
Shallots are at home in sauces. On the assertiveness scale, these mild-mannered relatives of garlic are similar to white onions, but their flavor is more refined and complex. Shallots are most often minced and added raw to a vinaigrette or cooked until sweet and used as the foundation of many classical and modern sauces.
The cut makes a difference
After you decide which onion to use, you need to consider how to cut it, as this has a dramatic effect on the final texture. If you want the onion to blend seamlessly into the dish, mince it. For a little more presence, dice it. If you want it to be unmistakable, slice it.
When slicing, I use the distinction of cutting the onion “with the grain,” from root to blossom end, or “across the grain,” which creates rings or half moons. When you cut with the grain, the onion slices hold together during cooking and retain their shape better. Onions sliced across the grain release more moisture and lose their crispness faster. I exploit this characteristic when I make onion soup by cutting half the onions across the grain (these partially dissolve and thicken the soup) and half with the grain (these give the identifiable onion texture to the finished soup).
Avoid bruising the onion, whichever cut you choose. A food processor or dull knife used to slice or chop through an onion will rupture more of the onion’s delicate cell structure, causing the release of more of its sulfur-containing amino acids. These come in contact with other enzymes in the onion, creating the sulfuric acid that makes you cry and makes the onion taste strong.
Two ways to slice an onion
Cooking tailors flavor
There are three basic ways to cook onions: sweating, sautéing, and caramelizing.
To sweat an onion is to cook it until it’s soft and translucent but hasn’t begun to brown. The purpose of sweating onions is threefold: It reduces the sulfur compounds (which softens flavor), it heightens the sweetness, and it softens the texture. Sweated onions lay the groundwork for dishes like braised meats, rice pilafs or risottos, and white sauces. They lend a natural sweetness that can’t be created by simply adding sugar.
Sweat onions over low heat and use only enough fat to coat the bottom of the pan. If you use significantly more fat, you’ll be “smothering” the onions, a related process usually reserved for béchamel (white sauce) and other sauces that are ultimately thickened with flour-and-fat roux.
Sautéed onions are cooked until they’re golden brown. They’re tender, but not as soft as sweated onions. Because they have a more resilient texture and a richer, sweeter flavor due to the browning, they’re great in dishes like vegetable sautés, pastas, and soups.
To sauté onions, use high heat and a minimum of fat. Heat your pan before adding enough oil or clarified butter to film the bottom of the pan and then add the onions. Don’t cover the onions while you’re sautéing. Covering the pan would trap steam, and the steam would keep the onions from browning.
Caramelizing onions creates a new depth of flavor. When the onions’ sugars caramelize, a complex chemical process produces more than a hundred new flavor compounds. Each has a color, aroma, and taste that combine to create a unique, soulful flavor that permeates a dish unlike anything else. Caramelized onions add color and depth of flavor to brown stocks, and they make a flavorful topping for pizzas, bruschetta, steaks, and chops.
If caramelization had a mantra, it would be “take your time.” This is a process that doesn’t happen quickly. Depending on the amount of onions, it can take upwards of an hour. But developing the flavor slowly is worth it; rushing may get you the color but much of the flavor will still be undeveloped, and some of the onions will be simply burnt.
To caramelize onions, combine the techniques of sweating and sautéing. The thicker the cut of the onions, the lower the heat should be in the final stage of caramelizing. If the onions ever start to look dry and appear to be browning to fast, stir in a little water to moisten them and to dissolve the sugars that are burning.