Shirley Corriher knew nothing about cooking until she and her husband opened a boys' boarding school and Corriher - a former chemist at Vanderbilt Medical School - found herself catering for 140. With the measured irony that only those blessed with a southern accent can achieve, Corriher describes the experience as a "trial by fire." Teenage boys are, she said at a lecture opening The New York Academy of Sciences' "Science of Food" series on October 26, "the ultimate restaurant critics."
Flummoxed by why her scrambled eggs stuck to the pan, Corriher was saved by her German mother-in-law, who taught her to pour eggs onto a hot, not a cold surface. This simple lesson was the first in a lifelong course of study. "Science is an indispensable part of our everyday lives, and nowhere is that more clear than in cooking," says Corriher, today a well-known culinary consultant who has now worked with luminaries such as Julia Child and Roland Mesnier, the White House pastry chef.
"You can't be a great cook without understanding the chemical properties of food and how it interacts with other variables, such as temperature, time, and the type of cookware used." Becoming a cook has also taught her about the relation of theory to practice: "From chemistry I know what is supposed to happen, and I also know from my pots and pans what really happens. I take what really happens and work backwards."
Corriher is author of Cookwise: The Hows and Whys of Successful Cooking (Morrow, 1997), which won a James Beard Award. For her, food is full of pedagogical possibility. "When you heat an egg white, it starts off translucent; you can see right through it until the protein bonds pop open. One protein runs into another with their bonds sticking out, they join together, and bam! The egg white turns white. This is chemistry you can see." It is also chemistry that you can taste. Everyone knows what happens when you overcook an egg; it turns rubbery. The explanation? When those protein bonds first join, they trap water, but if you keep heating, the water is squeezed out entirely.
This basic science also underpins the sophistication of sous-vide cooking. A fashionable and hotly debated technique, sous vide (literally "under vacuum") seals ingredients in plastic and slowly cooks them in a water bath at low temperatures. Some topnotch chefs dismiss the technique, including Alice Waters of Chez Panisse in Berkeley, Calif., who prefers a hands-on intimacy with ingredients. But other premier chefs favor it, including Thomas Keller of The French Laundry in Yountville, Calif. Cooking protein extremely gently avoids muscle-length shrinkage and substantial moisture loss, so the sous-vide method can lead to sublime textures. Done incorrectly, it can also lead to botulism. Placing food in anaerobic environments preserves cell structure and amplifies flavor, but it requires a kitchen run with the precision of a laboratory.
Cooks need scientists to understand the thousands of elements affecting food, including color. It is a culinary truism that blue food is not appetizing. But cherries in muffins sometimes have a blue halo, red cabbage can turn blue in the sauté pan, and Corriher recalls being asked to explain why walnuts stained a chef's fish with a nasty "blue drool." The culprit was anthocyanins. Three groups of compounds give red fruits and vegetables their color. Carotenoids are relatively stable (think pumpkin), and so are betalains (think beets). But anthocyanins are what Corriher calls "the problem children." Water soluble, they also lose their red hues when made too alkaline. If red cabbage turns blue while cooking, it is because its acids have evaporated. A teaspoon of vinegar will restore its scarlet. The blue cherries have reacted with the baking powder or baking soda in the batter. Substituting acidic sour cream for milk will solve the problem.
Acids will, however, be the death of green vegetables. Corriher set the scene: "There's your green bean, a happy little fellow, breathing in oxygen, breathing out carbon dioxide, just like us. He hits the hot water and he starts leaking acids like crazy. The pectic substances that hold his cell walls together begin dissolving, and before you know it, your bright green bean is army drab."