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First, find out how fresh the eggs really are. The freshest ones are the eggs that sink and lie flat on their sides when submerged in cool water. These eggs can be used for any dish. By the time the egg is a week old, the air pocket inside, near the broad end, has expanded so that the broad end tilts up as the egg is submerged in cool water. The yolk and the white inside have begun to separate; these eggs are easier to peel when hard-cooked. A week or two later, the egg's air pocket has expanded enough to cause the broad end of the egg to point straight up when you put the egg in water. By now the egg is runny and should be used in sauces where it doesn't matter if it isn't picture-perfect. After four weeks, the egg will float. Throw it away.
Eggs are easily contaminated with Salmonella microorganisms that can slip through an intact shell. NEVER EAT OR SERVE A DISH OR BEVERAGE MADE WITH RAW FRESH EGGS. SALMONELLA IS DESTROYED BY COOKING EGGS TO AN INTERNAL TEMPERATURE OF 145°F; EGG-MILK DISHES SUCH AS CUSTARDS MUST BE COOKED TO AN INTERNAL TEMPERATURE OF 160°F.
If you separate fresh eggs by hand, wash your hands thoroughly before touching other food, dishes, or cooking tools. When you have finished preparing raw eggs, wash your hands and all utensils thoroughly with soap and hot water. NEVER STIR COOKED EGGS WITH A UTENSIL USED ON RAW EGGS.
When you whip an egg white, you change the structure of its protein molecules which unfold, breaking bonds between atoms on the same molecule and forming new bonds to atoms on adjacent molecules. The result is a network of protein molecules that hardens around air trapped in bubbles in the net. If you beat the whites too long, the foam will turn stiff enough to hold its shape even if you don't cook it, but it will be too stiff to expand naturally if you heat it, as in a souffle. When you do cook properly whipped egg white foam, the hot air inside the bubbles will expand. Ovalbumin, an elastic protein in the white, allows the bubble walls to bulge outward until they are cooked firm and the network is stabilized as a puffy souffle.
The bowl in which you whip the whites should be absolutely free of fat or grease, since the fat molecules will surround the protein molecules in the egg white and keep them from linking up together to form a puffy white foam. Eggs whites will react with metal ions from the surface of an aluminum bowl to form dark particles that discolor the egg-white foam. You can whip eggs successfully in an enamel or glass bowl, but they will do best in a copper bowl because copper ions bind to the egg and stabilize the foam.