Harold McGee's first book, On Food and Cooking: The Science and Lore of the Kitchen, is a virtual bible of gastronomy, filled with scientific and technical information (e.g. "The Composition of a U.S. Large Egg" and "Some Prominent Edible Seaweeds") as well as practical advice based on the science (e.g. how to store various fruits and "Making Green, Oolong, and Black Teas"). The book's comprehensiveness, which makes it an essential reference tool, also limits it to that use.
McGee has written a new book, with the rigor of the first but more oriented to home cooks and the types of things they do. This mission of this book, Keys to Good Cooking: A Guide to Making the Best of Foods and Recipes, is in the title, and it succeeds admirably in fulfilling it. It does not contain recipes, but discusses how various things are cooked in a way that invites the reader to return, recipe in hand, for extra insight into the hows and whys (and sometime errors) thereof. For example, the chapter "Sauces, Soups and Stocks" contains useful information related to the production and storage of flavored oils, mayonnaise, vinaigrettes, salsas, meat and vegetable stocks, cream sauces, butter sauces, gravies and much more. I plan to review the section on gravies in preparation for next Thanksgiving, and am certain that my selection or execution of a recipe, or both, will benefit.
The way to make optimal use of this valuable work is to read it quickly from cover to cover, although there will be sections that you may wish to omit - there is no law requiring you to read about making candies if that's something you are sure you'll never do - and then to go back to it when you are actually planning to prepare or store something and want to maximize the knowledge that you bring to the task. Believe it or not, the full-read is enjoyable; McGee is a New York Times columnist and knows how to write.
Like McGee's first book, Keys to Good Cooking is a valuable addition to any cook's shelves.