Many onion varieties seem interchangeable -- considering most recipes call for something less-than-specific, like "one onion, chopped." That universal treatment of onions probably holds true most of the time, but you can make a dish sing that much more by using the right onion for the job. Here is our short, handy guide to onions.
Remember to store dry onions in a dry spot like a countertop or basket. Fresh onions, like leeks and scallions, should go in the fridge. Most people don't know that dry onions freeze nicely. Feel free to chop them up, bag them, and stuff them in the freezer.
Guide to Onions
Yellow onion: Pungent, common, flexible. Not sure that's how any one of us would want to be described, but yellow onions (brown onions in Britain) are the utility player of the onion family. These sauté up nicely and can handle caramelization beautifully. They're also readily available.
White onion: White flesh and a strong taste make them standouts in Mexican recipes. They can also be sautéed to a deep brown color. It might be an old wives' tale, but some sources say these stay a bit crisper, even when cooked.
Maui onion: Amazingly sweet, juicy onions and, yes, grown in Maui, Hawaii. They have a high water content and are shaped like flattened globes. They make amazing onion rings and are great for when you really want to taste onion versus just flavor a dish. Maui onions might look like dry onions, but they should be handled more like a fresh onion (i.e., a leek or scallion).
Red onion Juicier, sweet and red-fleshed with a mild flavor -- sometimes called a Bermuda onion. These onions tend to be medium to large in size, and can stand up to being grilled or lightly cooked with other foods. They tend to become dull if you sweat them or sauté them heavily. They make an excellent marmalade.
Shallots: These grow in clusters and are purple in color. Much milder and more subtle flavoring. If a recipe calls for a shallot -- use it! It's not wise to substitute an onion there, although if you're in a pinch, you could substitute a green onion.
Spring onion: Varieties abound -- yellow, white or red -- but all varieties have a thin, light-colored skin that bruises easily. They are sweet and delicate which means they are best when used lightly, as in salads and gently cooked dishes.
Vidalia, Walla Walla, Spanish... the list keeps going. Remember to heat up onions under moderate flame, as they tend to become bitter at higher temps. Really, though, who among us doesn't?