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What makes an onion work?

What makes an onion work?

Like a bomb, an onion holds power, heat,surprise. Cut it, and it explodes with strong smells, hot flavors, and irritating vapors. But detonate the firepower, and it can be meek and mild--even sweet.

The key is understanding an onion's structure.With this knowledge, any cook can manipulate this versatile bulb to achieve pleasingly specific results. With help from Dr. Ruth Tanner, chemistry professor at the University of Lowell, Massachusetts, and a professional chef, we explain how this works and give cooking techniques for dry onions; for more recipes, see page 210.

The variety of possible tastes and texturesis impressive. Onions have been cultivated as a food since at least 3000 B.C. Mexicans like the hot bite of raw onions as a condiment, the Chinese stir-fry them, the Danes deep-fry them, and Indians use them as a mellow base for curries.

Onion structure and onion chemistry

Onions come in many different colors andsizes, but all are the same species. The dry bulbs, the vegetable we're exploring here, are 89 percent water and 8 to 9 percent soluble sugars; the rest is minerals, fats, proteins, and sulfur compounds.

The sulfur compounds produce distinctiveflavor and an aroma that can be difficult to disguise once you've eaten or touched onions. These oil-soluble compounds easily remain in the oils on your skin. They're also blood-soluble and so can be detected in breath and perspiration.

Some onion compounds do not form untilyou break cell membranes. As soon as a cell is broken, as by peeling, bruising, or cutting, a definite sequence of reactions follows. A key component is the enzyme alliinase (see drawing at left). The degree to which this enzyme is activated affects the intensity of the response.

First, sulfur-containing compounds areproduced; these are responsible for irritating vapors, one of which stimulates a tear response, and for a biting astringency. These compounds quickly break down into others, which ultimately yield the onion flavor and aroma. In raw or partially cooked onions, these compounds mask sugars and dominate taste.

How to control onion behavior

Cutting or breaking the cell membranesdevelops compounds associated with flavor, aroma, and bitterness. With more disruption, more of these compounds-- including lachrymator (tear producer)-- will be formed. To minimize this effect, peel onions under running water so you rinse away vapors and lachrymator as they are created. Chilling onions before you cut also slows the release of tear producer.

When you chop onions in a food processor,more cells are bruised than when you mince onions by hand--so the flavor is stronger and more bitter.

Cooking time and heat intensity both affectflavor. A short period of high heat brings out strong onion characteristics more quickly. But long cooking over low heat diminishes the strong taste, enhancing the onion's natural sweetness. Using too high a temperature for too long a time develops bitterness, which is somewhat different from a burnt flavor.

An onion's natural acidity affects color. Ifyou soak it in water or cook it in butter, acidity outside may be less than inside, causing its own acid to leach out and its color to change. This is a problem only with red onion: if you pour an acid like vinegar over it, it turns bright pink; in an alkaline solution (such as one containing baking soda), it turns yellow-green. To preserve the red color, outside acidity should match the onion's own natural acidity of about 0.3 percent; use a solution of 1 tablespoon vinegar to 2 cups water. Use more vinegar if the onion is to be cooked for a long time (heat accelerates loss of color) or soaked in a large quantity of water for a long time, or if you prefer a brighter pink color.

Saute: most flavor (not hot)

Sauteing or stir-frying cut onion overmedium-high heat brings out the most flavor. The high temperature volatilizes the first set of compounds, then speeds production of other compounds associated with onion flavor and aroma. Sugars in the onion caramelize, which lends color and flavor to sauces and stocks.

Heat also drives out the air between thecells, making onion pieces translucent. When vinegar or spices are cooked with them, as for bearnaise sauce, a curry base, or the onion-wine topping for steak (recipe on page 210), the collapsed onion cells soak up the added seasonings like a sponge.

Serve these mild but richly aromatic onionsover meats, as a seasoning starter for sauces, and to flavor vegetables.

Sauteed Onions

1 tablespoon butter, margarine, orsalad oil

1 large onion (3 to 3 1/2 in. wide),chopped

In a 10- to 12-inch frying pan, melt butterover medium-high heat. Add onion and cook, stirring often, until onion is translucent and edges are lightly browned, 5 to 7 minutes. Serve hot. Makes about 3/4 cup.

Slow-cook: sweet, mild, limp

Slow-cook sliced onions in fat over moderateheat until they become very limp and golden. Slicing brings forth flavor components; long gentle cooking dissipates them, unmasking natural sweetness. Some of the soluble onion sugars caramelize during cooking, deepening and enriching flavor.

Use the sweet onions as a base for soup, asa condiment for plain roasted or sauteed meats or poultry, or in sandwiches (see page 210).

Slow-cooked Onions

4 large onions (3 to 3 1/2 in. wide)

4 tablespoons butter or margarine

Thinly slice onions crosswise and separateinto rings. In a 12- to 14-inch frying pan, melt butter over medium-high heat. Add onions. Cook, stirring occasionally, until they are very limp, taste sweet, and turn golden, 20 to 30 minutes. If onions begin to brown, reduce heat to medium-low and stir more often. Serve hot.

If made ahead, cool, cover, and chill up to2 days. To reheat, stir onions in an 8- to 10-inch frying pan over low heat until hot. Makes 3 to 4 cups.

Whole: mellow and mild

If onion is cooked uncut, hot flavor fromits enzyme, alliinase, never develops; you get only mild onion flavor with slight sweetness.

A whole onion can be roasted or grilled. Ifit is peeled or cut in half, the sugars caramelize slightly on the outer surfaces, and a richer flavor develops. With roasted onion halves, you can add a little vinegar to the pan; its tartness counterbalances the onion's sweetness.

Eat whole onions in their skins with roastedor grilled meats; they can cook alongside for a simple vegetable accompaniment. Slice in halves to serve; allow one or two halves for each portion.

Whole Roasted Onions

Place 6 large onions (3 to 3 1/2 in. wide) ina shallow 3-quart baking pan or 9- by 13-inch pan. Bake in a 350| oven until they feel soft when pressed, 50 to 60 minutes. Cut in half and serve with butter or margarine and salt and pepper to taste. Makes 6 to 12 servings.

Roasted Onion Halves

Cut 3 large onions (3 to 3 1/2 in. wide) inhalf lengthwise. If desired, pour 1/4 cup balsamic or red wine vinegar into a 9- by 13-inch pan. Place onions, cut sides down, in pan.

Bake in a 350| oven until soft whenpressed, 30 to 45 minutes. Serve with butter or margarine and salt and pepper to taste. Makes 3 to 6 servings.

Grilled Onions

Place 6 large onions (3 to 3 1/2 in. wide) ona grill 4 to 6 inches above a solid bed of medium-hot coals (you should be able to hold your hand at grill level only 3 to 4 seconds).

Cook, turning often, until onions feel verysoft when pressed, 1 to 1 1/4 hours. Cut in half to serve with butter or margarine and salt and pepper to taste. Makes 6 to 12 servings.

Boil whole: sweet, mild

When small, whole, peeled onions areboiled in water, the onion produces a compound much sweeter than sugar. As with baked whole onions, alliinase's hot flavor doesn't develop.

Serve small boiled onions with butter or ina cream sauce or buttery broth glaze (recipe on page 212).

Boiled Whole Onions


16 to 18 small peeled onions (1 1/2 in.wide)

Butter or margarine

Salt and pepper

In a 3- to 4-quart pan, bring 1 1/2 to 2quarts water to boiling. Add onions and simmer, covered, until tender when pierced, about 20 minutes. Drain. Add butter, salt, and pepper to taste. Makes 4 to 6 servings.

Deep-fry: crisp, sweet, golden

Cut onion into thin shreds, lightly dustwith flour, and fry in a generous amount of oil. The large surface area exposes sulfur compounds. The hot oil drives off many of them and much of the onion's moisture, leaving crisp sweet shreds.

Serve fried onions for a snack, on grilledmeat patties or chops, or on open-faced sandwiches (see page 212). They can be cooked ahead and reheated.

Crisp-fried Onions

2 large onions (3 to 3 1/2 in. wide)

1/2 cup all-purpose flour

Salad oil


Peel and thinly slice onions. Separate intorings. Pour flour into a bag. Add onions and shake to coat evenly with flour.

In a deep 2 1/2- to 3-quart pan, bring 1 1/2inches oil to 300| on a thermometer. Add onions, shaking off excess flour, about 1/4 at a time, and cook, stirring often, until golden, about 5 minutes. Regulate heat to maintain it at 300|.

With a slotted spoon, lift out onions anddrain on paper towels (discard any scorched bits). Sprinkle lightly with salt. Serve warm or cool. If made ahead, package airtight and chill up to 3 days. To reheat, spread in a single layer in a 10- by 15-inch pan and bake in a 350| oven until warm and crisp, 2 to 3 minutes. Makes 5 to 6 cups.

Raw: crisp and hot, or crisp and not so hot

Many people like the mild bite of crisp,raw onion in salads or with hamburgers. To minimize harshness, it helps to use a variety generally recognized to be sweet, such as Maui, Vidalia, or Walla Walla. Many of these are as much as 12 percent sugar--as sweet as an orange.

Because sweet varieties develop little orno lachrymator, they cause no tears and develop relatively weak onion flavor. They are best raw; cooked, they taste so mild as to seem neutral. In most onions, the lachrymator produces antibacterial and antifungal qualitites that account for the long storage life. But the kinds without lachrymator potential spoil quickly when bruised. To minimize bruising, wrap onions individually in paper. Keep them in a cold place, at just above freezing.

High-sugar onions have a short season, soit's helpful to know how to use other varieties raw. But how do you select an onion to eat raw? Shape, color, size: none of these is a consistent indicator of mildness. Even within a single onion, flavor can vary. Growing conditions appear to affect taste more: generally, onions grown with little water tend to taste hotter. Appearance is no clue.

We've found two ways to tone down harshflavor in any onion, and also preserve crisp texture. Immerse thin slices in ice water until crisp, 20 to 30 minutes, to rinse away some of the hot flavor and tear-producing compounds. The result will be pretty, crisp slices. But when you bite into them, you will again break cell walls, initiating a new set of reactions. A hot onion will still have some heat.

Or squeeze the slices in water to break upcells and wash away more of the stronger-tasting compounds. Drain, then chill in ice water; water plumps crushed cells and gives crisp texture. These somewhat battered-looking slices will have milder, more consistent flavor, because more of the cells have been broken, releasing and washing away harsh flavor.

Prepared either way, the slices have definiteonion flavor with a degree of bite, if not harshness, that depends on the individual onion. Use in salads, sandwiches, and relishes (see page 210).

Crisp Raw Onion Shreds

1 large onion (3 to 3 1/2 in. wide)


2 cups ice cubes

1/4 cup vinegar

Peel and thinly slice onion. Place slices ina bowl and add tepid water to cover. For milder flavor, squeeze with your hands until onions are almost limp. Drain, rinse, and return to bowl. Add ice, vinegar, and about 2 cups water. Let stand until crisp, 20 to 30 minutes. Drain well. Lift out onion. Makes 3 to 4 cups.

Photo: Regardless of color or size,dry onions have similar structure and chemical composition and behave the same way when you use them for cooking

Photo: Elements of an onion's taste are withineach cell. When you cut into cell, enzyme alliinase starts chain of chemical responses; sulfur gives distinctive flavor and aroma

Photo: Onion bulb consists of concentricshells of leaf bases swollen with stored water and sugars. Cells also hold small amounts of minerals, fats, protein, sulfur compounds

Photo: 1. Chop, saute for definite onion flavor

Saute onions over medium-high heat until limp, thenadd wine to make topping for steak (recipe on page 210)

Photo: 2. Slice, then cook slowly for sweet mellowness

Cook sliced onions over moderate heat until limp, golden, and sweet. Pile atop ham and cheese on toasted rye for sandwich (page 212)

Photo: 3. Bake whole for mildness

Bake onions in their skins for mild flavor; slice inhalf to serve plain or with butter. Recipe below

Photo: 4. Boil whole for sweetness

Boiling gives onions mild sweetness. Trythem cooked in broth (see page 212)

Photo: 5. Deep-fry for crisp rings

Fry rings until crisp. Use onsandwiches (see page 212)

Photo: Rinse, then chill--to eat raw

Squeeze, wash, and crisp slices to eatraw, as in relish (recipe on page 210)
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