As stated, meringue is a whipped mixture of egg whites and sugar but it’s a little more complicated than that. Beating egg whites imbibes them with air molecules, thus inflating them and producing a foam. But the air can escape and deflate the meringue. Ergo, the goal is not only producing a foam, but a stable one. Here’s a point by point guide:
In an electric mixer with the whisk attachment, or with a hand-held whisk, make the meringue as described next.
Room temperature eggs will whip faster and produce greater volume than cold ones.
Ensure that there is not a trace of egg yolk in the whites when you separate the eggs. The slightest bit of fat can interfere with the whipping of the whites.
Copper bowls produce greater volume than any other material because of the chemical reactions between the copper and the egg whites.
Adding a pinch of cream of tartar (tartaric acid) enhances the stability. Use a 16th of a teaspoon per white. If not using a copper bowl, definitely use cream of tartar. Get the whites started and then promptly add the cream of tartar.
Use superfine sugar which incorporates better. You must wait for the whites to reach the “soft peak stage” which is a limp foam, before adding the sugar. Moreover it must be added a tablespoon at a time. Adding it too soon or too quickly compromises the final volume.
A pinch of salt is sometimes added for flavor. Again, wait for the soft peak stage as salt actually decreases the foam’s stability.
Continue beating the whites once all the sugar and salt is added but do not over beat them or they can curdle. Scoop out some of the meringue with the whisk and hold it up. If the peaks hold their shape, you’re done. This is the stiff peak stage.
Mix the vanilla extract in toward the end.