When a skillet of onions is sautéing, everyone who walks into the house asks, “What smells so good?” Whether the onions are browning quickly to garnish a steak sandwich, caramelizing slowly for a tart filling, or simply softening as the base for a soup, stew, or sauce, their olfactory appeal is universal. Not even garlic, another member of the onion family, whets the appetite as satisfyingly.
Onions (Allium cepa) are essential to all of the world’s cuisines. Their bulbs come in a variety of shapes—round, flattened, torpedo—and colors—red, white, and yellow. Mature onions range in size from tiny pearl onions and the small flat onions (cipolline) that Italians pickle to giant bulbs the size of soccer balls. In addition, some do not form bulbs at all or are harvested when immature as scallions (these are also called green, spring, or bunching onions). Most of these have a white stalk and green top, but at least one cultivar, Red Beard, has a red stalk. All tend to be mild in flavor.
Each form of onion has named cultivars that are prized for their particular flavor, which may be mild, sweet, or hot. Regional and seasonal specialties include Bermuda, Maui, Sweet Spanish, Texas 1015, Vidalia, and Walla Walla. The Bermuda onion can be hot, while the rest are known for their surprising sweetness and are good eaten raw. As one can tell from some of the names, these onions are grown in particular areas where the soil and climate affect their sweetness. Add leeks (A. porrum), with their thick, white, mild-flavored stalks, and shallots (A. ascalonicum), whose bulbs separate into cloves with a mild garlic flavor—close relatives to garlic that are used similarly in cooking—and it is clear that the art of cooking would be unrecognizable without the versatility that these plants allow us in the kitchen.
To cook without onions is like playing a symphony without strings: it can be done, but the results do not resonate so harmoniously, for cooked onions provide a sweet and broad flavor foundation for thousands of dishes.
Raw onions are another kind of music altogether, offering sharp accent notes and piquancy. Many people who love cooked onions cannot abide them raw. It is the sulfur compounds in onions that cause their pungency as well as tears while chopping them. The strength of these compounds varies according to variety, time of year, and growing conditions of soil and climate. When the onion is cut, the sulfur compounds are changed into volatile sulfides (see “Eat Your Onions” on page 38), which make our eyes water and our noses burn. Cooking the onions makes them sweet. We’ve tried many of the folk methods to prevent crying—keeping the mouth firmly closed and holding a burned match between the teeth, for example—but have found nothing as effective as rinsing the onions under cold water immediately after cutting them. Some cooks advocate cutting onions under running water, but that can be awkward. If you are planning to use the onions raw and they still taste hot after rinsing, soak them in a bowl of cold water with a pinch of salt for fifteen to twenty minutes, then rinse again. This treatment appears to wash away most of the sulfur compounds. It can also be used for leeks and shallots if these cause you tears.
Onions, leeks, and shallots go well with any of the culinary herbs; particularly in simple dishes, herbs are a great enhancement. Thyme with roast onions, dill in cucumber and onion salad, marjoram in onion stuffing, leek and potato soup with chervil, sage and onion focaccia: these are just a few examples in the realm of herb and onion combinations.
Many markets offer a limited selection of onions: white, yellow, and red bulbs, and scallions. During the winter, most of the bulb onions for sale are hot; their concentrated sulfur compounds make them good keepers. Keep storage onions in a cool, dry place. The sweet varieties have a higher water content and thus are milder but don’t keep as well. To prevent these sweet varieties from sprouting, store them in a dry crisper drawer in the refrigerator for up to six weeks. Scallions keep about one week in the refrigerator.
As home gardeners, we’ve experimented with the wide range of onions, leeks, and shallots that can be grown from seed or sets. Enriching the soil with organic matter encourages the formation of good-sized bulbs, while banking soil up against the leeks produces long white tender stalks.
Onion bulbs enlarge in response to day length, with different cultivars having different requirements. Long-day onions require 14 hours or more of daylight, intermediate-day onions 12 to 14 hours, and short-day onions 11 to 12 hours.
Bulbing onions are usually offered in seed catalogs by day length, which corresponds to latitude. If you live at about 40° north latitude or above, choose long-day varieties. Short-day varieties grown in your latitude will begin forming bulbs too early, and mature bulbs will be small. In the South (32° north latitude and below), you’ll need to grow short-day onions. During cool weather (when onions grow best), the days are too short for long-day onions to form bulbs, and when the days are long enough, the temperature is too high for bulb formation. In these latitudes of mild winters, onions go into the ground in fall, grow through the winter, and begin forming bulbs when the days lengthen in spring. In the middle regions (between 40° and 32° north latitude), intermediate varieties do best. If you live near the border between two regions, you may be able to grow onions from two categories. Scallions, leeks, and shallots can be grown in all regions.
After you have determined the category appropriate for your region, choose the types of onions that appeal to you most: sweet, hot, large bulbs or small storage onions and/or scallions. White Sweet Spanish, Southport White Globe, and Ebenezer are three bulbing onions that are commonly harvested when immature (about 60 days from sowing) as scallions. Don’t neglect to order some shallots and leeks, too. Onions, leeks, and shallots take from 85 to 180 days from sowing to harvest. Check the catalogs to see which kinds are suitable for your region and whether they should be planted in spring or fall.
You may sow any onion outside in well-drained soil in full sun as early as possible in spring, or sow seed in flats six weeks before you want to set the onions out, or purchase onion sets or plants. Sets and plants have the advantage of yielding a harvest a month to six weeks before seed-sown onions, though there is not a large selection of varieties available in these forms. Whatever kinds of onions you grow, keep them well watered and weed-free. Onions are heavy feeders. For optimum growth, they need light fertilizer at sowing or transplanting time and monthly fertilization with a 10-10-10 fertilizer.
Withhold water when the onion or shallot tops start to fall over. When about half of the tops are down, push over or break the rest; some people do this by walking on them. Harvest about a week later. Shake off the dirt and spread them on screens or racks in partial sun (full sun may produce sun scald) with good air circulation. Let them cure for one to two weeks, bringing them inside or covering them at night if there is dew or rain. After this curing period, trim the necks to within 1 inch of the bulb and trim any long roots. Store 1 to 2 months in a cool, dry place with good air circulation. Ideal storage temperature is 35 to 50°F, though up to 65°F is acceptable. Storage onions can be kept for up to four months under these conditions. Look for signs of deterioration or rotting. If new roots appear on alliums that are in storage, the environment is too moist; if the tops sprout, the temperature is too high.
Are your taste buds ringing and your nose tingling for onions? Before sitting down with your seed catalogs, try one of our simple, winter-warming recipes. While you prepare it, your house will be filled with good smells, and you can daydream of bumper crops of onions, leeks, and shallots from the garden.