By Teresa Marrone
Onions are so ubiquitous as a flavor enhancer that we often fail to see them as a vegetable that’s useful in its own right. But they are just that. A list of the great dishes of the world would be incomplete without French onion soup, which is, basically, a bowl of caramelized onions mixed with some good broth. Oh, and a nice toasty crouton… and a pile of gooey Gruyère cheese, too. But truly, onions are the star: meltingly soft, rich brown, and as sweet as sugar.
How can a vegetable that makes the cook cry while cutting turn into a sweet delight that makes diners smile while eating? This transformation is due to what food scientists call the Maillard reaction, a complex chain of events involving the interaction of amino acids and natural sugars when exposed to heat. The Maillard reaction is responsible for the sweet brown goodness of a cream puff, the mahogany skin on the Thanksgiving turkey—and the rich, deep flavor of caramelized onions.
Onions do have a natural sweetness, if you can get over the sharp, pungent notes (and the crying factor, which is caused when sulfur and enzymes in the onion combine when the cells are broken during cutting, producing an irritating gas—there, now you know!). Well-known “sweet” onions, such as Vidalia, Walla Walla, and Maui, have less sulfur and a higher water content; these are ideal for slicing to top a burger or other dishes that call for raw onions. They are at their peak in summer, although some store fairly well and are available through mid-winter. Note that these particular onions have controlled growing areas; a true Walla Walla onion is from Washington state, Vidalias are grown only in Georgia, and Maui onions hail from Hawaii. So what’s a sweet-toothed, burger-loving locavore to do?
Fortunately, we do have locally grown onions that are naturally sweet; white onions tend to be sweeter than yellow onions, and many—but not all—red onions are less pungent. Sweet varieties tend to be thin-skinned, regardless of color; onions with thick, rind-like layers of skin tend to be more pungent. Yellow Globe is a sweet yellow variety that grows well in Minnesota; other locally grown sweet onions include Sweet Spanish, Superstar, and Candy.
So-called “storage” onions are harvested in fall, and can be kept through winter in cool, dry conditions. These include the humble yellow onion, which is probably the most common find in the onion bin. Yellow onions are great for all-purpose cooking. Once you get past the tears of chopping, their full flavor is appreciated in sauces, stews, sautés, and other cooked dishes. For salsa and other dishes that require uncooked onions, white or red onions are a better choice. You can also sweeten onions a bit by tossing them with a little vinegar and salt, then letting them stand for ten minutes before giving them a quick rinse. Storage onions that grow well in Minnesota include yellow onions such as Big Daddy and Frontier, and red onions like Greek Salad and Red Burgermaster.