Onion
The humble onion is the aromatic backbone of countless dishes, adding sweetness, depth, and savory complexity to almost any meal.
In a nutshell
Onions are one of the most widely used vegetables in American cooking, prized for the way they transform from sharp and pungent when raw to mellow and sweet when cooked. They form the flavor foundation of everything from weeknight stir-fries to slow-simmered stews. With almost no fat and a modest calorie count, they add enormous flavor for very little nutritional cost.
Nutrition
≈ 5 Calories and 0g fat per tablespoon.
Onions are a decent source of vitamin C and B vitamins, particularly folate and B6, which support immune function and energy metabolism. They’re rich in quercetin, a potent antioxidant flavonoid linked to reduced inflammation and heart-health benefits. The fructooligosaccharides in onions act as prebiotics, feeding beneficial gut bacteria. Their organosulfur compounds — the same chemicals that make your eyes water — are associated with potential anti-cancer and cholesterol-lowering properties. At only 40 calories per 100 grams with virtually no fat, onions are a nutrient-dense, low-calorie way to build bold flavor. Nutrition per 100 g.
Culinary uses & pairings
Raw onions add a sharp, assertive bite to salads, salsas, sandwiches, and slaws. Soaking sliced raw onion in cold water for 10 minutes mellows the pungency considerably without sacrificing crunch. Yellow onions are the workhorse for most cooked applications — dice them as the aromatic base for soups, braises, and sauces, or slice them thinly for caramelized onions, which take at least 45 minutes of patient, low-to-medium-low heat cooking to develop their rich, jammy sweetness.
Onions are essential to stocks and broths, often halved and charred directly on the stovetop to add color and depth. They pickle beautifully in a quick brine of vinegar, sugar, and salt, becoming a vibrant topping for tacos, burgers, and grain bowls. Whole roasted onions — simply wrapped in foil and cooked at 400°F (205°C) until tender — make a surprisingly satisfying side dish on their own.
Pairs well with
Substitutions
Buying & storage
Look for onions that feel firm and heavy for their size, with dry, papery outer skins and no soft spots, sprouting, or visible mold. The neck (top) should be tight and completely dry — any moisture there is a sign of age or improper storage. Avoid onions with a strong smell through the skin, which suggests the flesh has begun to break down. Larger onions are easier to dice efficiently, making them a practical choice for everyday cooking.
Varieties
- Yellow Onion: The American kitchen workhorse. Pungent when raw, it turns deeply sweet and golden when cooked, making it ideal for caramelizing, soups, and stews.
- White Onion: Sharper and more intensely flavored than yellow; common in Mexican and Southwestern cooking, and preferred raw in salsas and guacamole.
- Red Onion: Milder and slightly sweet with a striking purple-red color; best enjoyed raw in salads and sandwiches or quick-pickled, as the color fades and the flavor softens considerably with heat.
- Sweet Onion (Vidalia, Walla Walla, Maui): Grown in specific low-sulfur soils, these have a noticeably high sugar content and gentle flavor that makes them exceptional eaten raw or lightly cooked.
- Pearl Onion: Marble-sized and mild; traditionally used whole in braises, pot roasts, and creamed onion dishes. They’re tedious to peel fresh, so frozen peeled ones are a perfectly good shortcut.
- Cipollini Onion: Small, flat, and very sweet Italian-style onions that caramelize beautifully when roasted or braised whole; a favorite for elegant side dishes.
Recipes using onion
3549 recipes across our recipe sites use onion. A few favorites:
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History & origin
Onions have been cultivated for at least 5,000 years, making them one of humanity’s oldest crops. Ancient Egyptians considered them sacred, placing them in burial tombs and depicting them in temple art; according to ancient accounts, workers who built the pyramids were reportedly provisioned with onions, garlic, and radishes. They spread throughout the ancient world via trade routes, becoming a staple in Greek, Roman, and Chinese cuisines. European explorers introduced cultivated onions to the Americas, though Indigenous peoples of North America were already using native wild onions long before contact. By the 19th century, onions were a foundational vegetable in American farm cooking, and today the United States grows billions of pounds of them annually across states like California, Idaho, Oregon, and Washington.
How it’s made
Onions are cool-weather crops started from seeds, transplants, or small dormant bulbs called sets. They are sensitive to day length — short-day varieties thrive in southern states and are harvested in late spring, while long-day varieties are grown in northern states and harvested in late summer. As the plant grows, its leafy tops photosynthesize and send energy down to form the fleshy layered bulb. When the tops naturally fall over and begin to dry, farmers know the bulbs are mature. After harvest, onions are cured — left in a warm, dry, well-ventilated environment for several weeks — so their outer skins dry into the papery layers that protect the bulb during long storage and transport.
Good to know
- Onions make you cry because cutting them ruptures cell walls and releases enzymes that react with sulfur compounds, producing a gas called syn-propanethial-S-oxide that irritates your eyes; chilling the onion before cutting significantly slows the reaction.
- The word ‘onion’ traces back to the Latin unio, meaning ‘unity’ or ‘oneness,’ a term Romans used for a single large onion as distinct from the clustered cloves of garlic.
- Onions are among the most consumed vegetables in the United States by volume, with Americans eating roughly 20 pounds per person per year.
- Caramelizing onions properly takes far longer than most recipes admit — a true deep-brown, jammy caramelized onion requires at least 40 to 60 minutes over medium-low heat, not the 10 minutes many recipes suggest.
- Onion skins, typically discarded, are rich in quercetin and are used by many cooks to add golden color and flavor to homemade stocks and broths.
