Today, my guest is Harold McGee, a food scientist who writes about the chemistry and history of food, science and cooking.  A distinguished Caltech alum, he earned his Ph.D. from Yale University before becoming a food science writer.  After writing his first book On Food and Cooking in 1984, it was extensively revised in 2004.  Today, he writes a regular column for the New York Times which examines, and often debunks, conventional kitchen wisdom; and also teaches at The French Culinary Institute in New York City and Harvard University.