of a medium onion

The onion (Allium cepa L.) is a bulbous perennial plant belonging to the Amaryllidaceae family, native to Central Asia. The edible bulb consists of concentric layers of fleshy leaves surrounding a central shoot, covered by a papery outer skin (tunic) that ranges in color from golden-yellow to red or white depending on variety. Medium onions typically weigh 150–250 grams. The flavor profile is pungent and sharp when raw, becoming progressively sweet and mellow with cooking as sulfur compounds break down and sugars caramelize. Common varieties include yellow Vidalia, Spanish, and Texas onions (mild and sweet), red onions (moderately pungent with slight sweetness), and white onions (sharper, more assertive flavor).

The aroma derives from volatile sulfur compounds (primarily S-methyl methane thiosulfate) that irritate the eyes when the onion is cut. These compounds are responsible for both the characteristic smell and much of the flavor. When onions are heated, enzymatic and thermal reactions convert these sulfur compounds into sweeter, more complex compounds.

Onions are a foundational aromatic in countless cuisines worldwide, serving as a base for stocks, soups, sauces, and stews. They are used both raw and cooked; raw in salads, salsas, and crudités where they provide crispness and pungency; and cooked through sautéing, roasting, caramelizing, and grilling, where they develop sweetness and depth. They feature prominently in French mirepoix, Italian soffritto, Spanish sofrito, and Indian masala preparations. Medium onions are versatile for everyday cooking, suitable for slicing into rings for frying, dicing for sauces and fillings, or halving for roasting. Caramelization over low heat for 30–45 minutes develops rich umami flavors essential to French onion soup and other classic dishes.