Chemical Warfare

• Garlic, onions and their relatives -- a branch of the lily family -- are no-nonsense practitioners of chemical warfare. They extract trace quantities of sulfur from the soil, and transform it into a series of defensive chemicals. When they're bitten, cut or crushed, enzymes in their cells react with those sulfur compounds to produce a range of burning, intense, volatile substances. Insects and most animal pests are either deterred or incapacitated by this assault on their senses. Humans are more adaptable, and have come to enjoy the strong flavors of onions, garlic and their kin. Ironically, humans select and eat these plants precisely because of the chemicals intended to protect them.

The Stinky Rose

• Garlic's great culinary virtue is its ability to make other foods taste better. It brings out and complements the rich and savory flavors in meats, poultry, fish, vegetables, herbs and spices with equal deftness. This makes it an indispensable ingredient in most of the world's cuisines. Garlic aficionados sometimes refer to it as "the stinky rose," because it's as vital to a kitchen garden as the rose is to an ornamental garden. Used raw it adds a sharp and pungent flavor to salads, dressings and condiments. When cooked, garlic becomes noticeably mellower and more versatile.

The Science of Mellow

• The sulfur compounds that give garlic its flavor are highly volatile. They form quickly in response to crushing or cutting, and rapidly disperse into the air. This volatility, or ability to react with the air and other chemicals, is what causes them to change and mellow when they're cooked. At a chemical level the sulfur molecules rapidly break up, recombine and change under stress from the heat of cooking. As they do, they form more complex flavor molecules that give the cooked garlic its distinctively rich, nutty and mild taste. As the sharpness dissipates, the naturally occurring sugars in the garlic come to the forefront and make it taste sweeter.

Temperature and Technique

• How you cook the garlic affects the chemical reactions that take place, and the flavor that results. Garlic cooked whole is mildest, because there are fewer chemical reactions. Roasting a whole bulb of garlic in its skin gently steams it in its own moisture and caramelizes some of its sugars. This gives it a creamy texture and rich, nutty flavor. Butter's saturated fats don't react readily with garlic's sulfur compounds; sliced or minced garlic cooked slowly in butter retains much of the same gentle character. Oil interacts more with the garlic, creating a more pungent flavor than garlic cooked in butter. High heat creates very strong, harsh flavors in garlic. Burnt garlic is not salvageable and can ruin your dish, so dispose of it and start over.