Onions are so familiar that it seems impossible that there could be anything at all complicated about them. In fact, nothing is simple about this most basic of vegetables. Study them very long, and you may feel you’ve followed Alice down some fragrant rabbit hole. What seems to be one fairly consistent family turns out to be a wide and varied collection of many overlapping clans that parade under a bewildering assortment of names.
Onions can be red, white, yellow or green. They can be as big around as a softball or as tiny as a hazelnut. Some are even buttonshaped. They can be called Spanish, Bermuda or Italian; spring, picklers, creamers, pearls or boilers. They can be sweet (those compose a virtual atlas—they can be from Maui, Walla Walla, Vidalia, Texas or the Imperial Valley, among other places). And then there are all those alliaceous cousins—garlic, shallots and leeks. Making sense of so many choices can be maddening.
Where to start? Probably the most important thing to know is whether they are sold fresh or dried. The vast majority of onions in the marketplace fit the latter category. They are grown to full maturity before harvesting; indeed, picking doesn’t start until the bulbs have developed their full capacity of sugar and their green tops have withered and flopped to the side. A kind of chain dragged behind a tractor “undercuts” the onions, destroying the root systems and finishing the job. Usually, the fields are then mowed, removing the tops, and the bulbs are left to dry for more than a week before being harvested. Finally, the onions are removed to sheds, where fans circulate warm air constantly over the top. This curing process removes moisture, which can encourage fungi. Curing also sets the papery skin, which acts as a barrier against moisture and injury, further reducing the chances of spoilage. During this process anywhere from 3 to 10 percent of an onion’s total weight is lost.
But onions also have a built-in mechanism for extending their shelf life, one with profound benefits for cooks. Most alliums are high in sulfurous compounds that naturally inhibit spoilage. Perhaps more important, however, these compounds give onions and their kin their distinctive character. Depending on the balance of specific components, the flavor can range from the sharp, grassy green of spring onions to the sweet mellowness of leeks to the orotund bass note of garlic. The base elements that form the flavors of most alliums (S-alkenyl derivatives of L-cysteine sulfoxide, if you really want to know) are constant. But the trace elements (1-propenyl-1, 2-propenyl-1, 1-propyl and methyl-L-cysteine sulfoxide) change, and those provide the distinctive differences.
What’s really amazing is that in many cases those distinctive flavors—and even the chemical compounds that create them—are produced only when the flesh of an allium is bruised or cut. That damages the plant’s cell walls, allowing the contents to combine. Enzymes react with existing compounds to create new ones, starting a split-second chain of chemical reactions that results in what we instantly recognize as onions’ taste and smell.
The most common storage onions are the round brown ones (called yellow onions) that we often buy in big bags. They last the longest and tend to have the highest concentration of sulfur. White and red storage onions (both are sometimes called “Bermuda,” which was once an important center of onion agriculture) tend to be slightly more delicate in flavor and don’t store as well because they contain less sulfur. For this reason, they are frequently used raw. These are both round onions, but particularly in Italian neighborhoods, you can also find red onions shaped like torpedoes. These taste pretty much the same as round red and white onions. Small storage onions—called pearls, picklers, creamers, boilers and babies, depending on their size and the whims of marketers—come in all three colors as well. They are grown tightly packed together to limit their size. They all taste pretty much the same as well; their big draw is visual. The primary exception is the small, flattened Italian cipolla (also known by the diminutive “cipolline”), which has a fuller, rounder, sweeter flavor.
Other onions are picked fresh. The most common of these are the familiar pencil-shaped green onions. They are sold under a confusing variety of names—spring onions on the West Coast (though they are available year-round), scallions (on the East Coast) and, peculiarly, shallots (in Louisiana). Green onions are usually harvested well before they reach maturity and have begun to form a swelling bulb. Most important to a cook, they are picked before they have developed either much sulfur or much sugar. Their taste is mildly sharp and green (from the high chlorophyll content). Green onions also can be picked at the bulb stage, when the flavor is a little more developed. These are especially good for cooking whole, as the slightly larger size allows a pleasing range of textures.
To compound the confusion, there is also a branch of the family called “bunching onions.” They look much the same as green onions, although their tops are a little more structured—when you slice them, they come away perfectly round rather than elliptical. The flavor is noticeably fuller and less pointed, as well as a little sweeter, than that of green onions. The king of the green onion is the Japanese variety called negi or nebuka, which is grown buried in the earth, like a slim, sharp leek. And then there are chives, which look like extremely fine green onions but are actually a separate species (Allium schoenoprasum). And garlic chives, which are still another species (Allium tuberosum). And that’s not even addressing leeks (Allium ampeloprasum), which we’ll get to later.
A third group of onions falls somewhere between storage and fresh onions. They are large and somewhat flattened and look like brown storage onions, but their shelf life is almost as short as that of the tenderest scallion. Indeed, these are the only onions that can truly be considered to have a season. So-called sweet onions are harvested and consumed in the spring, whether you’re in Maui, Hawaii, or Vidalia, Georgia, or anywhere in between. These onions aren’t so much sweet as they are low in sulfurous compounds (which is why they must be eaten right away and need to be refrigerated, whereas storage onions don’t). They might more properly be called mild, not sweet, onions, and they are sometimes perilously close to being bland. In fact, whereas normal brown storage onions typically have a sugar concentration of about 12 percent, sweet onions average closer to 8 percent.
Perhaps because of their even lower concentration of harsh sulfurous compounds, well-grown sweet onions have an appeal that is almost fruity. They can be eaten raw, out of hand, just like an apple. In fact, they should be—cook them, and you only emphasize their lack of character. They are crisp, with just a little of the background burr that lets you know that you are, after all, eating an onion. And they cry out to be sliced for sandwiches or cut up for salads.
Sweet onions are a triumph of vegetable marketing. The first to achieve notoriety was grown in the early 1930s near Vidalia, Georgia, by a farmer named Moses Coleman. Vidalia was the local market center and was also the distribution center for a couple of major supermarket chains. Liking the local product, the supermarket managers began shipping it out to other member markets as early as the 1940s. By the 1970s more than 600 acres of sweet onions were being harvested in the area, and the farmers banded together to form a marketing cooperative. Because the Vidalia farmers were so successful, their neighbors in the nearby town of Glennville began promoting their own sweet onion. After a little intrastate sparring about who produced the sweetest onions (and facing even more competition from sweet onion growers from outside the state), the groups decided to unite and battle the world as one. Today more than 14,000 acres of so-called Vidalia onions are planted in a wide swath across the state of Georgia.
So popular are they that at least half a dozen other places market sweet onions of their own. In reality, not much differentiates those grown in Georgia from those grown in Maui, South Texas or almost anywhere else for that matter. They are almost all the same variety, usually called Grano or Granex, depending on the specific strain. This variety was developed in Texas from seed originally imported from the island of Tenerife off the coast of Spain. Scientists at a state-sponsored agricultural experimental station crossed this onion with another to come up with a whole string of sweet onions that they eventually exported to growing areas around the country. The sole exception is the sweet onion from Walla Walla, Washington, which has a somewhat tangled lineage. Walla Walla Sweets (it is a copyrighted trademark) descend from Italian seed acquired on the island of Corsica by a French soldier. He brought it to the United States when he immigrated in the early 1900s and introduced it to Walla Walla’s Italian farmers.
Just because sweet onions are grown in so many places doesn’t mean they can be grown anywhere. An onion’s character is the result of a combination of genetics and environment. Some onion varieties tend to be more pungent than others. But a normally mild onion grown in the wrong place can pack something of a wallop or, alternatively, have no more flavor than water. Three environmental factors affect onion flavor. First is the chemical composition of the soil. Just as that distinctive onion flavor comes from sulfurous compounds, the strongest onions are grown in soil that is rich in sulfates. Second is watering. The strongest flavor belongs to onions that get the least water. Finally, temperature during the growing season can affect the pungency of an onion: the hotter the temperature, the hotter the onion. Most onions are planted in the spring and harvested in the fall, but sweet onions are planted in the fall in places where they can overwinter, to take advantage of the cooler temperatures.
As tangled as the whole onion family might be, that is just the beginning of the allium confusion. You also have to think about all those fragrant cousins—shallots, garlic and leeks.
Shallots look like brown pearl onions, except they are a bunching variety. This means that if you plant one shallot, you’ll grow a whole clump of shallots, which will be joined at the base, with one side noticeably flattened where it grew next to its neighbor. This point is important to remember. There are onions that look quite a bit like shallots and are often sold as shallots. But they are not shallots, and the first clue will be that they lack that bottom junction scar and one flat side. Don’t be fooled; they will also lack shallots’ depth and complexity of flavor.
Garlic is so varied that it probably deserves its own family tree. Walk a farmers’ market, and you might spot as many as half a dozen different varieties. Although each garlic has its own slightly different characteristics, there are two major families that you need to know about. The first type grows with a strong central stem, which remains after drying. This is called “hardneck” or rocambole garlic. It has the most varied and interesting flavors.
Through domestication, another family has been developed that lacks the strong central stem. It is called “softneck” garlic and is the dominant commercial type. Softneck garlic is easier to plant and grow, and it’s certainly easier to pack and store. The trade-off is that the flavor isn’t as good and clove size can vary tremendously within the same head. Elephant garlic is an entirely different species, close kin to the leek. Although it is large, its flavor is so mild that it’s called “garlic for people who don’t like garlic.”
Leeks look like giant green onions. Unlike their smaller relatives, however, they are grown to full maturity. They retain their white bases by careful maintenance during the growing season. As soon as a little white becomes visible on the stem, dirt is piled around the leek. This shields it from sunlight, which in turn prevents the formation of chlorophyll (which would add a vegetal note to the flavor). This continuous piling on of dirt tends to make leeks extremely gritty; they must be washed thoroughly before you do anything with them. But any effort required is more than repaid by the results. Once leeks have been cooked, the flavor is deep and round, with a lingering sweetness. The texture is pure silk. This is one regal allium.
WHERE THEY’RE GROWN: California is the predominant state for onion farming, whether you’re talking about storage onions (more than 25 percent of the U.S. crop), green onions (almost 50 percent) or garlic (more than 80 percent). Leeks and shallots are not tracked. Imports are also an important part of the picture. More than 10 percent of the storage onions consumed in the United States come from outside the country—mostly Mexico, Canada and Peru. Americans also import more than 20 percent of all the garlic used, with China accounting for more than half of that.
HOW TO CHOOSE: Storage onions should be well filled, with the peel adhering to the bulb. There should be little shrinkage and no visible fungus (black dusty stuff). Avoid onions with green sprouts. Green onions should be fresh, with no decay at the tops and little shedding of the white peel. When green onions begin to get old, they are often trimmed, so check that the base is as wide as the root. When buying leeks, look for the same thing you do with green onions. Remember that the white part is what you eat, so the higher it goes on the stalk, the better off you are. Garlic should be well filled and solid. If the paper covers the cloves loosely, that’s a sign of the shrinkage that comes with drying out. There should be no sprouting. Shallots should be well filled with a tight-fitting peel. Remember to check the base for the root scar and make sure one side is flattened to ensure that you’re getting true shallots.
HOW TO STORE: Storage onions, shallots and garlic should be stored in a cool, dry place away from light. Sweet onions should be refrigerated, as should green onions and leeks.
HOW TO PREPARE: The easiest way to peel storage onions and shallots is to cut off the root and the top, leaving a strip of skin attached at each end. Pull down on that strip, and you’ll create an opening in the paper from which you can easily peel the rest of the onion. Garlic can be broken out of the head by placing the head root end up on a cutting board. Press down firmly with the heel of your hand, and the cloves will pop free. To peel a clove, lay it on the cutting board and whack it just hard enough to bruise it with the flat of a chef’s knife. That tight-fitting peel will come off easily. Because leeks are grown in mounds of dirt, they require special care in cleaning. Cut off the roots, leaving the base intact. Cut off the tough green leaves (these can be frozen to use in stock). Leaving about 2 inches of the base intact, cut the leek lengthwise into quarters and rinse it well under running water. Inspect it carefully for any hidden grit.
ONE SIMPLE DISH: Caramelized onions are a preparation that belongs in every cook’s repertoire. They are easy to make and endlessly versatile: add a little cooked bacon or slivered prosciutto, and you have a pasta sauce; top a pizza with caramelized onions and goat cheese, and you have a feast. Caramelizing onions is basically a matter of long, slow cooking, but there are a couple of tricks that make it easier. Slice the onions into rings that are ¼ to ½ inch thick, depending on how long you want to cook them and how much texture you want at the end (thicker equals longer with slightly more bite). Put them in a cold, heavy skillet with just enough olive oil to lightly cover the bottom of the pan. Start them cooking over medium heat. When the onions have softened a little, salt them, cover the pan and reduce the heat to low. The salting will draw moisture from the onions; the lid will concentrate the heat. Cook them, stirring every 10 to 15 minutes, until limp and beginning to color, about 45 minutes. Raise the heat slightly and remove the lid. They will finish coloring in another 5 minutes. If you want to add garlic (something I heartily recommend), do it only at the last stage. Garlic contains much less moisture and will scorch a lot earlier.