Separating the myths from the realities of cooking information can be as tricky as separating the yolks and whites of eggs. Does it really help to add salt to egg whites before beating them? Will searing meat seal in juices during the roasting? In fact, performing these rituals may reassure the cook but will accomplish little else. Salt actually increases the whipping time required to turn egg whites into snow, and it decreases the stability of the final result. Searing meat does nothing to retain juices, although it does improve the flavor.
That is the sort of invaluable, fundamental information provided by Harold McGee in his 684-page volume On Food and Cooking: The Science and Lore of the Kitchen (Scribners; $29.95). Gathering data from experiments of others and performing many of his own, McGee has put together an exhaustive account of foods of all sorts with facts on their chemistry and physical properties, translated into correct cooking methods.
The best sections are those dealing with dairy products, eggs, meats and fish. In his introduction on the lore of the egg, McGee writes that at one point in history, eggs existed before chickens. He hastens to explain that by egg he refers to the specialized container of the ovum of early organisms that predated all birds by millions of years. Pleasant rambling through history makes good reading, but the author's practical information is more illuminating. For instance, beaten egg whites are important to cakes and soufflés because they hold air that expands as it heats. Yolks, which hold only small amounts of air when beaten, are primarily binders and, because of their fat, enriching moisturizers. McGee also explains that, in cooking eggs, it is important to avoid extensive coagulation, which produces a rubbery texture or curdling. He therefore advises a moderate, gradual heating that will not cause the proteins to contract and squeeze out the liquid they are supposed to retain. In other words, when making hollandaise sauce, use a gentle heat so the sauce will thicken smoothly.
McGee's description of the differences between the muscle fibers of fish and those of meat makes it clear why seafood is naturally tender whereas meat needs cooking to become easily chewable. Detailed diagrams of molecular structures and cross sections of tissues are always related to cooking and eating properties. A reader with a less scientific turn of mind can skip the theory and get almost as much from the applied information. Never mind the cell structure of beef: anyone attempting to broil a very thick cut will find that the surface is burned long before the interior can be cooked. And whatever the molecular construction of a given cheese may be, a hard, well-ripened one like Cheddar can tolerate higher cooking temperatures without becoming tough and stringy than can a soft cheese like Brie.