What Type Of Onions Are Typically Used In French Onion Soup?

Onions are a foundational ingredient that can seem almost magical the way they make a dish with their distinct aromatic flavor — or break it with their absence. Of course, not all onions taste the same. On the contrary, each type has its own distinct properties, which is why certain dishes work best with particular alliums. You”ll find that the bold, zesty flavor of red onions is preferred in certain instances, whereas other recipes call for the sharp, bright, piquancy of white onions.

When it comes to French onion soup, traditionalists reach for the yellow ones, and with good reason. That's not to say that you can't make the deliciously rich cheese-topped soup with other types of onions — or a combination of different types of onions – but if you're looking for straightforward, authentic flavor, yellow is the way to go. The sweet yet pungent variety will yield the best results, whether you're making slow-cooker French onion soup or going all out with an au gratin recipe.

Indeed, French chef Jacques Pépin likes to use yellow onions when whipping up his version of the dish. In a YouTube clip from PBS' "American Masters: At Home with Jacques Pépin," the culinary icon masterfully turns a single large onion into two deep, filling bowls of soup.

Whereas red onions are best for marinating or serving raw on salads and white onions make fantastic salsas and taco toppings, yellow onions are ideal for cooking. Not only do they maintain their shape through long periods of extensive heat exposure, but the subtle sweetness they have when raw intensifies nicely when they're caramelized — making them ideal for French onion soup.

In addition to yellow onions, sweet Vidalias — which are also known as Maui onions — make a great alternative. Sweet Vidalias are also yellow and they caramelize exceptionally well. So, while they don't give French onion soup quite the same balance that regular yellow onions do, they will work in a pinch. Ideally, the two can be combined if you don't have enough standard yellows on hand, or if you would like the soup to turn out slightly sweeter. Overall, however, yellow onions are a requirement for a classic, bistro-worthy French onion soup.

When it comes to making French onion soup, caramelizing the onions correctly is crucial. Not only does caramelization bring out the sweetness, but it creates just the right silky soft texture. This process works best with yellow onions for two reasons. The first is their high sugar content, which helps with browning. But secondly, there's the beautiful golden color that results. Whereas caramelized red onions turn a drab gray, yellow onions will take on varying degrees of gold to deep brown depending on how long they're left to caramelize — resulting in a beautiful soup.

These degrees of coloration are also super helpful for knowing when the onions are ready. While a deep golden color signifies the perfect sweetness, if they're left on the heat to the point where they reach a too-dark brown, that's a sign that they may develop bitterness (not necessarily what you want for French onion soup). By using yellow onions and caramelizing them to a perfectly golden hue, you'll get a perfectly balanced soup with just the right amount of savory sweetness.