Sweet Onions vs. Yellow Onions: What's the Difference?

No savory dish is really complete without an onion. The culinary staple provides texture, aroma, and a deep flavor that complements myriad ingredients. But not all onions are equal—and you might find yourself choosing between sweet and yellow varieties at the supermarket. At first glance, they look similar, but the alliums boast varying features that can affect your final dish. We spoke to culinary professionals to learn the difference between sweet onions vs. yellow onions, plus whether they're interchangeable in cooking.

What Is a Sweet Onion?

As the name suggests, sweet onions have a sweet taste. According to Nadia Minniti, chef-instructor of online culinary arts and food operations at the Institute of Culinary Education, common varieties of sweet onions in the U.S. include:

• Vidalia
• Walla Walla
• Texas Spring Sweet
• Maui

What Is a Yellow Onion?

Yellow onions have a pale yellow flesh. Common varieties in the U.S. include the following, according to Minniti:

• Bridger
• Copra
• Cortland
• Patterson
• Pontiac
• Talon
• Yellow Globe
• Spanish

The Differences Between Sweet Onions vs. Yellow Onions

There are five basic ways these two types of onions differ.

Flavor

The main difference between sweet onions and yellow onions is flavor. This is due to varying levels of sugar and sulfur-containing compounds, which are responsible for the pungent flavor of onions.

Overall, sweet onions have slightly less sugar than yellow onions. However, they contain more fructose, which is the sweetest tasting type of sugar, says Rosemary Trout, DHSc, program director and assistant clinical professor of culinary arts and food science at Drexel University. Sweet onions also have less sulfur-containing compounds, resulting in a more prominent sweetness, says Trout.

In contrast, "yellow onions have more sulfur-containing compounds, which mask the sweetness," adds Trout. The result is a more intense and spicier flavor.

Appearance

"Sweet onions are slightly flatter and not as round as yellow onions," says Minniti. They're also a bit larger. Meanwhile, yellow onions have a rounder shape. They can also be as small as a medium lemon or as big as a softball, she says.

Color

"The color of sweet onions varies from white to yellow, except for the Tropea sweet onions from Calabria, Italy, which are red," explains Minniti. But take note: "Just because a sweet onion is yellow in color doesn't make it a yellow onion. The sweet flavor and difference in shape make a sweet onion as such," she adds.

As for yellow onions? They have orange papery skin with a pale yellow flesh, notes Minniti.

Shelf Life

Sweet onions have a slightly higher water content than yellow onions, resulting in a shorter shelf life, says Trout. Thus, they should be stored in the refrigerator for several weeks, while yellow onions can be stored at ambient or slightly cooler for several months, she says.

The varying levels of sulfur-containing compounds play a role, too. In addition to providing a pungent flavor, these compounds act as a defense mechanism against pests and molds, says Bryan Quoc Le, Ph.D., food scientist, food consultant, and author of 150 Food Science Questions Answered. Yellow onions contain more of these compounds, which protect against spoilage-causing microorganisms and prolonging shelf-life. Sweet onions have lower levels, so they have a weaker defense mechanism, according to Le. The result is a shorter shelf-life.

Best Cooking Applications

Sweet onions are best for roasting, caramelizing, and grilling, according to Minniti. "They're also great for onion rings due to their larger size," she adds. On the other hand, "yellow onions are better suited for dishes that require long cooking times over low heat, such as soups, stocks, stews, and in sauces, [and] they're perfect for risotto and sautéing," says Minniti.

Can You Substitute One for the Other?

Good news: If you need a sweet onion but only have yellow (or vice versa), you'll be glad to know that they're interchangeable, according to Minniti. Still, there are a few things to keep in mind when making the swap:

• Cooking time: Since sweet onions contain more moisture than yellow onions, they need to be cooked longer to ensure the water sufficiently evaporates, says Minniti.
• Sweetness: When used in place of yellow onion, the extra sweetness from sweet onions might interfere with your recipe's flavor profile Minniti says. On the other hand, if you're using yellow onions in place of sweet ones, you can cook them for a long time over very low heat to help them develop some sweetness, she says.

Which Is the Best All-Purpose Onion?

If you're cooking your own recipe and choosing between sweet onion vs. yellow onion, reach for the latter. Yellow onions are often touted as an "all-purpose" onion due to their versatility. Compared to other varieties, "they're more intense, pungent, spicy, and savory overall, but still brown and mellow nicely because they're higher in concentrated sugars," says Trout. Plus, yellow onions are more convenient to have on hand thanks to their longer shelf life.