Onions

The onion is believed to have originated in Asia, though it is likely that onions may have been growing wild on every continent. Dating back to 3500 BC, onions were one of the few foods that did not spoil during the winter months. Our ancestors must have recognized the vegetable's durability and began growing onions for food.

The onion became more than just food after arriving in Egypt. The ancient Egyptians worshiped the onion, believing that its spherical shape and concentric rings symbolized eternity. Of all the vegetables that had their images created from precious metals by Egyptian artists, only the onion was made out of gold.

Today, onions are used in a variety of dishes and rank sixth among the world's leading vegetable crops. Onions not only provide flavor; they also provide health-promoting phytochemicals as well as nutrients.

Selection

Most onions are sold loose by the pound, although some types are sold in bags or small boxes. Look for onions that feel dry and solid all over, with no soft spots or sprouts. The neck should be tightly closed and the outer skin should have a crackly feel and a shiny appearance. Onions should smell mild, even if their flavor is not. Avoid selecting onions with green areas or dark patches.

Storage

Onions should be kept in a cool, dry open space away from bright light. Onions do best in an area that allows for air circulation. Because onions absorb moisture, do not store onions below the sink. Also, do not place onions near potatoes because potatoes give off moisture and produce a gas that causes onions to spoil more quickly. Spring/summer onions usually store for about two weeks and storage onions for about three to four weeks.

Varieties

Onions came in a variety of sizes, colors and shapes. They are often broken down into three categories: spring/summer, storage, and pearl onions. Spring/summer onions are grown primarily from fall to spring in warm weather areas and have a soft flesh and a mild or sweet taste. These varieties are generally shipped right after harvesting. Storage onions have a firm flesh, dry, crackly outer skins and have a pungent flavor. After a brief period of drying, these onions are stored for several months before shipping. Pearl onions are often called white onions and are densely planted to make the onions smaller. There are no nutritional differences among these onion types.

Onions also come in three colors - yellow, red, and white. Approximately 88% of the onion crop is devoted to yellow onion production, with about 7% red onions and 5% white onions.

Yellow onions are full-flavored and are a reliable standby for cooking almost anything. Yellow onions turn a rich, dark brown when cooked and give French Onion Soup its tangy sweet flavor. The red onion, with its wonderful color, is a good choice for fresh uses or in grilling and char-broiling. White onions are the traditional onion used in classic Mexican cuisine. They have a golden color and sweet flavor when sauteed.

Preparation

Onions may be eaten raw or cooked. Onions should be peeled before preparing, except when baking. Onions may be boiled, braised, baked, microwaved, or sauteed.

Onions and crying

As onions are sliced, cells are broken, allowing enzymes called alliinases to break down sulfides and generate sulfenic acids (amino acid sulfoxides). Sulphenic acids are unstable and decompose into a volatile gas called syn-propanethial-S-oxide. The gas dissipates through the air and eventually reaches the eye, where it reacts with the water to form a dilute solution of sulfuric acid. This acid irritates the nerve endings in the eye, making them sting. Tear glands produce tears to dilute and flush out the irritant.

Supplying ample water to the reaction prevents the gas from reaching the eyes. Eye irritation can, therefore, be avoided by cutting onions under running water or submerged in a basin of water. Rinsing the onion and leaving it wet while chopping may also be effective. Chilling or freezing onions prevents the enzymes from activating, limiting the amount of gas generated. Using a sharp blade to chop onions will limit the cell damage and the release of enzymes that drive the irritation response.

The volume of sulphenic acids released, and the irritation effect, differs among Allium species.

Consumption of onions may cause some people to worry about "onion breath." Although this problem normally comes from eating raw onions, a mild raw onion may cause no odor. Cooked onions help alleviate this problem and leave virtually no odor on the breath. Here are a few helpful ways to freshen your breath:

Rinse your mouth with equal parts of lemon juice and water.
Chew a citrus peel to sweeten the breath.
Eat a sprig or two of parsley, nature's natural breath sweetener.

Source:
National Fruit & Vegetable Program
National Onion Association
Scientific American
Wikipedia