Why Eat It
Nutrition Chart

Why Eat It

Onions are low in calories and, to be truthful, in most vitamins and minerals (although they do supply a little calcium, iron, and potassium). However, the many flavorful members of this plant family-- scallions, leeks, shallots and garlic as well as onions themselves--are rich sources of a number of phytonutrients. They contain allyl sulfides (sulfur compounds that may lower blood pressure and discourage tumor growth), quercetin (a flavonoid with high antioxidant activity), and saponins (substances connected with cholesterol-lowering and tumor inhibition).

Onions originated in prehistoric times and were widely consumed in ancient Egypt, Greece, and Rome. By the 17th century, Europeans were enjoying them as a salad ingredient and as a breakfast "health" food. Today, onions rank sixth among the world's leading vegetable crops.


Onions and their relatives are known botanically as alliums, a plant genus that has been classified at different times as belonging to the lily family, the amaryllis family, or to a family all its own called Alliaceae. There are more than 500 alliums; all of the edible species are bulbing plants with a characteristic pungent smell or taste, which is produced once their layers of skin are cut.

Slicing onions come in an impressive array of sizes, colors, and shapes. Because onions are easily crossbred, growers are continually developing new varieties and hybrids. The ubiquitous medium-sized yellow globe onions, which are available year round, encompass many different varieties, with subtle differences in taste or texture. Whatever names are bestowed upon onions, though, they fall into two general categories: spring/summer onions and storage onions.

Spring/summer onions: Grown primarily from fall to spring in warm-weather states, such as Texas, Georgia, and Arizona, these onions have soft flesh and a mild or sweet taste. Some are designated by names referring to their growing areas, such as California Italian Red, Vidalia (from Georgia), Walla Walla (from Washington), or Maui Sweet (from Hawaii). Granex and Grano are other names denoting sweet onions with flattened or top-shaped bulbs. These varieties generally are not stored, but are shipped almost immediately after harvesting. Many of them are quite juicy and, because of their relatively high sugar content, mild enough to be eaten raw.

Storage onions: These have firm flesh, dry, crackly outer skins, and pungent flavors. Grown in northern areas of the United States, such as Idaho, Colorado, and New York, they are harvested in late summer and early fall. After a brief period of drying out (a process known as "curing"), they are stored for several months; they are available at markets from late fall to early spring. In stores, these onions may simply be labeled by color--yellow, red, or white. "Spanish" onions are a variety of very large storage onion, distinguished by their mild flavor and skin color, which ranges from yellow to purple. There are no nutritional differences among these types.

Pearl onions: Also called white onions, these are actually white pearl-shaped bulbs from different varieties. They are so densely planted that they attain a size of only 1 inch or less in diameter. "Boiling" onions are larger pearl-like onions that grow to 1 to 1 1/2 inches in diameter.


Storage onions can be found year round in ample quantities. The mild spring and summer onions are in greatest (but still limited) supply from March until September. Pearl and boiling onions are in good supply year round.


As a rule, the large, mild spring and summer onions are good for eating raw or for cooked dishes in which you want a subtle flavor. The crisp, assertive character of storage onions makes them better-suited for dishes that require long cooking, since they can hold their flavor. An onion's flavor is determined by its variety, and also by the soil and climatic conditions where it grows. Consequently, onions with the same appearance can taste considerably different, depending on where and when they were grown. So you may have to experiment, particularly when it comes to choosing the mildest onions.

Many shoppers prefer a particular color, though color is not a reliable guide to flavor or texture. (White onions tend to be more pungent than yellows or reds, but this rule of thumb may not be true in your area.) Size is another consideration: For raw onion slices in salads and sandwiches, select large onions. They are also a more efficient choice for peeling and chopping. For cooking whole or in wedges, choose small- to medium-size onions.

Most onions are sold loose by the pound, though globe and pearl onions also come in mesh bags. (Pearls are frequently packaged in small boxes.) Whatever type you choose, look for ones that feel dry and solid all over, with no soft spots (a sign of rot) or sprouts. The skin around the neck should be tightly closed, and the outer skin should have a crackly feel and a shiny appearance. Whole onions should smell mild--even those that are pungent when you cut into them; a strong odor is a sign of decay. Also avoid onions with green areas, which can taste unpleasant, or with dark patches, which may indicate mold.


Whole onions should be kept in a cool, dry, open space, away from bright light (which can turn their flavor bitter.) They do best in an area that allows plenty of air to circulate around them, so either spread them out in a single layer or hang them in a basket. Onions will absorb moisture, causing them to spoil more quickly, so don't store them under a sink (which can be damp) or place them near potatoes, which give off moisture and produce a gas that causes onions to spoil more quickly. Storage onions can last three to four weeks under these conditions, spring and summer onions about half as long. High humidity, though, will considerably reduce storage time. If an onion begins to sprout, use it quickly, since it has probably started to turn mushy.

You can extend the life of spring and summer varieties by storing them unwrapped in the refrigerator crisper; dry storage onions should not be refrigerated for more than a few days, and only if there's no other place for them. Leftover cut portions of fresh onion, wrapped tightly in plastic, will keep for two to three days if refrigerated. Cooked onions, tightly covered, can be kept for up to five days; store them in glass or plastic containers (metal can discolor the onions).


Chopping or slicing an onion brings its sulfur-containing amino acids into contact with enzymes to form volatile compounds, one of which strikes the tongue, while another irritates the eye, apparently by turning into sulfuric acid. The older an allium is, the stronger these compounds become. Fortunately for our taste buds, cooking produces further chemical changes that render them much milder. (Some of the odor compounds appear to be converted into a substance that is 50 to 70 times sweeter than table sugar.)

Onions can be sliced, chopped, diced, or grated, but first they must be peeled. To make this task easier (if you need to prepare a large quantity of onions), trim off the tops and bottoms and place the onions in boiling water for about a minute. Drain them and pull off the outer skin, which should be loose, then peel off the slippery membrane underneath. With small white boiling onions, cut a cross in the root end of each one, which keeps the onion intact once you slip off the skin.

Although some recipes call for raw onions to be cooked with other ingredients, others require them to be cooked beforehand. Virtually every cooking method has been used with onions; since they are low in nutrients, the length of cooking time is not a problem.

Baking: Use whole, unpeeled onions. Cut off the root ends, so the onions will stand upright in the baking pan, prick them with a fork, and place in a baking pan lightly coated with nonstick spray. Or, peel the onions, pierce them, and wrap in foil. Cook in a 350°F to 375°F oven; test for doneness by pressing the onions, which should give easily without feeling mushy. Cooking times: for medium-sized onions, 45 to 60 minutes. Storage onions generally take longer than the more loosely layered spring and summer onions.

Boiling: This method is best for whole and half onions, but also works for sliced onions. Cooking time: 10 to 35 minutes, depending on size and density of the onions.

Braising: This method works well for small white pearl or boiling onions. Place the onions in a pan and cover with 1/2" of water or broth. Simmer, covered, over low heat until the liquid is absorbed and the onions are tender. (Add more liquid if necessary.) Cooking time: 25 minutes.

Microwaving: Peel and quarter a pound of small- to medium-sized onions. Arrange them in a microwaveable casserole dish, adding 2 tablespoons of water or stock. Rotate once during cooking. Cooking time: seven to eight minutes.

Sauteing: Sauteing can be done in oil, or you can use stock or wine. The key is to keep the heat low and stir constantly. If the onions begin to brown too quickly, reduce the heat further and add 1 to 2 tablespoons of water. Cooking time: five to 10 minutes, depending on how finely chopped the onions are.

Nutrition Chart

Onions/1 medium

Total fat (g)
Saturated fat (g)
Monounsaturated fat (g)
Polyunsaturated fat (g)
Dietary fiber (g)
Carbohydrate (g)
Cholesterol (mg)
Sodium (mg)

Date Published: 04/20/2005
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