- Caramelizing onions longer builds deeper, more complex soup flavors.
- Yellow onions are best for balanced flavor, but shallots and sweet varieties also work well.
- Try this slow-cooking method with mushroom, lentil or minestrone soups.
We’re well into the chilly season, so if you’re like our EatingWell editors, you’ve probably already eaten your way through a few pots of your favorite soups. Before you whip up the next batch, though, there’s a tip our editors turn to for building big flavor that you should know.
The tip—giving onions more time to caramelize—appeared on a recent Reddit post that quickly went viral. While it’s a classic cooking technique used in a variety of dishes, you may not have thought to apply it to your go-to soups, other than French onion.
The Soup Tip, Explained
The original poster revealed that they had finally discovered why their mother’s soups always taste “deeper and more comforting” than their own: she allows the “onions [to] cook way longer in the oil before adding anything else.” They further explained, “She doesn’t just soften them, she lets them get golden and slightly caramelized. It’s like the onions become this sweet, savory base that transforms the whole flavor.” They said it is a technique they now use when making all kinds of soups.
No specifics on cooking time or temperature were given, but based on their description and what we know about making caramelized onions, it likely takes 30 to 45 minutes over low heat. That’s typically what’s needed, along with a bit of oil or butter, for onions to release some of their moisture and sugar and develop a deeply sweet and savory flavor profile and buttery texture. “That caramelization infuses the whole soup, making the flavor more complex,” says Senior Editor Megan Ginsberg, noting that she has used this method when making Thomas Keller’s Onion Soup from Bouchon.
What Soups Does This Tip Work With?
This technique can be used in a variety of soup recipes, including umami-forward mushroom soup and comforting classics like lentil soup. For recipes that call for a mirepoix base, like a traditional minestrone soup, Editorial Director Carolyn Malcoun’s approach proves useful: “I usually [cook] the onions until they have some color, then add the celery and carrot, so the celery and carrot don’t overcook yet I still get perfect onion magic.”
For soups that require a longer caramelization process, like the Bouchon soup that Ginsberg enjoys, you’ll need to set aside an entire afternoon, but the results will be well worth it. “The recipe calls for cooking and caramelizing yellow onions with a little butter and salt for 5 hours! (You keep the heat very low, and you have to stir them every 15 minutes.) The onions go from spilling out of the pot to shrinking down to just cover the bottom of the pot, and they become a deep, dark brown and get supersoft. The end result is an onion soup with a richer, meatier flavor than other onion soups,” says Ginsberg.
What Types of Onions Work Best?
Malcoun says she has caramelized a variety of onion colors, but she typically opts for yellow or white when making soup. Yellow onions are widely available and the top choice for caramelizing thanks to their high sugar content, which allows for deep browning and their slight bitterness that helps create balanced flavors when reduced. When shopping, look for conventional yellow onions with a globe shape or Spanish varieties.
Sweet onions, including Vidalia and Walla Walla, are inherently good for caramelizing. They have the highest sugar content, so you can expect even sweeter results after they are cooked down. Red onions will work in a pinch, but they won’t get as brown, and white onions are lower in sugar and have a crunchier texture, so they typically require added sugar and an even lower and slower cook. And while shallots grow in clusters with papery skin and involve a bit more prep, their high sugar content and nuanced flavors make them a great choice for this technique.
The Bottom Line
Making more flavorful soups can be as simple as caramelizing the onions before adding additional ingredients to the pot. The low-and-slow method draws out moisture and sugars, reducing the onions to a silky texture and bringing out complex, jammy flavors. You can try this technique with your favorite soup recipes and a variety of onion types, including shallots for even sweeter results.
