Eggs are easier to separate when they are cold. Carefully crack each egg and, holding it over a bowl, pass the yolk back and forth between the shell halves, letting the whites fall into the bowl. Drop the yolk into a separate bowl, and transfer the whites to a third bowl. Separate each additional egg over the empty bowl, for if any speck of yolk gets into the whites, the whites will not whip up properly. If a yolk breaks, start fresh with a new egg. Egg whites will keep for up to 5 days in the refrigerator or several months in the freezer.