When you’re in the grocery aisle looking at the piles of onions there to choose from, you probably have no idea which variety is best for you. They all appear similar… White and yellow bulbs, some sweet versus others called “red” that seem to have a bolder flavor. Here’s what makes them different, and how their varying chemical makeup means some are better cooked, while others is better raw. It will help you make smarter shopping choices and savor every meal.
When it comes to onions, should they be raw or cooked? That’s really the main rule of all onion-land. More important than what brand you buy. Onions contain sulfur compounds that is released upon cutting; these compounds are responsible for the sharpness of a raw yellow onion (the most popular variety in kitchens). In the cooking process, however, those sulfur compounds breaks down into deliciously sweet sugars. This is why yellow onions are so frequently used; you can caramelize them and soften them until they’re a deep brown to serve as base for soups. A raw yellow onion would of be overpowering in a salad.
How to Pick the Right Onion
There’s another onion type: the white. Unlike yellow, it’s sharper and crisper, and has a clean flavor that holds up well raw (think pico de gallo, guacamole). That is why it is popular in Mexican cuisine. Heat really affects the flavor of this onion, so it’s not the best choice for longer caramelizing periods when you want something deeply sweet.
Raw red onions has that same spicy kick but also add some color. They are great for pickles because they become pink and mellow a bit, too. But when cooked, they lose their color and turn an unappealing brown… Not a pretty sight on your plate.
Sweet onions are another matter; they’re mild enough that eating them raw won’t make you wince. Varieties of sweet onions (including Walla Walla or Vidalia) come from relatively low-sulfur soils, resulting in natural sweetness and lots of water. They are good for onion rings. Sweet onions do not store well. Refrigerate and use them promptly, within a few weeks; this is unlike their drier white- or yellow-bulb varieties which will store for months in a pantry. Prevent yourself from finding a slimy mess at the back of your fridge by knowing this.
Don’t ignore other alliums. Shallots combine more garlic-like with oniony flavors in an ethereal way. Used in sauces and vinaigrettes, they provides depth without a lot of kick. Leeks is buttery-tasting and mild, too, but be sure to wash them thoroughly (between each layer) before using, as grit can get trapped between those layers. Green onions and chives are even milder than leeks. Save these for garnishing or adding near the end of cooking; their fresh aroma will be lost if boiled too soon.
To do this, match the onion to the cooking technique. A special, sweet onion isn’t going to add much flavor to some thick broth… It’d be a shame to spend so much on it only to have its sweetness get lost. Likewise, why put a powerful yellow onion out raw when a milder green onion would suffice? It’s all about honoring the vegetable.
Once you know which onions are best eaten raw and which are better when heated, you’ll make smart choices instead of wild guesses. No more wondering what to do with that heap of bulbs, instead, you’ll use each one’s strengths. Next time you buy an onion, you’ll know why just that bulb is right for the job.