Keep in mind that different oils have different cooking properties. Most plant oils are volatile, changing quickly from fresh to rancid if not stored in a cool, dark place. Cooking at high temperatures can speed the breakdown of some oils and make them less healthy, or less pleasant-tasting. Oils such as grapeseed and avocado, which have particularly high smoke points—the temperature at which they begin to burn—are the best choices for frying. Most olive oil, meanwhile, is fine for low- and medium-heat techniques like sautéing and baking (olive oil cake is becoming a delicious staple of Italian dessert menus). Damian Sansonetti, the executive chef at Bar Boulud in New York City, poaches certain fish in oils. "Cod, for example, is a relatively lean fish," he says, "and it can be dry if it's pan-roasted. But poached in olive oil, it gets that nice, silky texture." He heats the oil just until "it's warm when you stick your finger in it," then lets the fish cook slowly, until it turns snow-white. Sansonetti also loves to sprinkle pine nut oil on lightly sautéed vegetables and fold hazelnut oil into pureed potatoes, and he adores pastry made with pistachio oil. "Oils add richness and a little flavor to food without altering the texture," he says.
It's not surprising that Sansonetti is such an oil aficionado. When he was growing up in Pittsburgh, his Italian grandmother sought out the finest olive oil available—then rubbed it on her skin. She didn't need a dermatologist, a nutritionist, or a physician to tell her what her ancestors already knew: that the human body is a machine that functions best when well oiled.