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.