Successful Meringue
Fat and water inhibit egg whites from being beaten to a stiff foam, so the bowl and whisk should be clean and dry.
The temperature of the ingredients is not vital to the success of the meringue, but if the egg whites are at room temperature rather than at refrigerator temperature they will be easier to whisk to a foam.
The proportion of sugar that is added determines the final texture of the meringue - 2 tablespoons of sugar per egg white produces a soft meringue, 4 tablespoons per egg white a hard one. Sugar helps to protect the meringue from drainage and collapse, but it also reduces the foaming of the egg whites, so it should not be added until the final stages of the whisking.
For more than two centuries, the use of a copper bowl has been recommended for whisking egg whites because it produces a good creamy foam that is more difficult to overheat, but just why this should he so remains a mystery. Theories that the copper gives acidity to the whites or that it establishes an electric field have not been substantiated.
The addition of a small amount of an acid, such as a pinch of cream of tartar or a few drops of lemon juice or a mild vinegar, help to guard against overheating and the overcoagulation of the egg whites, which results in lumpiness, collapse of the meringue and seeping of liquid.
Although salt, enhances the flavour of foods, it should not be added to meringues; it increases the time required to whisk the eggs to a loam and it decreases the stability.
