It's hard to crack open a pastry cookbook without encountering at least one recipe that calls for the use of French meringue. Since the seventeenth century, cooks have been using it as a natural leavening agent (an ingredient that provides rise and structure) for all kinds of desserts, including angel food cake, souffle, pavlova, baked Alaska, Eton mess and baked meringue cookies, just to name a few.
French meringue is one of the most simple, yet mysterious elements in the world of pastry. It consists of only four ingredients; egg whites, sugar, acid, and salt. These ingredients alone may seem unremarkable, but when combined together with the most critical element, forceful whipping, they become a marvel of chemistry and confection.
There are whole chapters of books devoted to the science involved, but for the sake of brevity, here's the quick and dirty version. Egg whites are mostly composed of water and proteins. When they're beaten, the normally tightly wound-up proteins (mostly ovalbumin) begin to unravel and stretch out, allowing them to link up with each other. This network of protein reinforces tiny air bubbles formed in the watery whites, creating a thick foam. As you continue to beat, the protein-strengthened walls of these bubbles are stretched thinner and thinner as more and more air is introduced until a critical ratio of air to water in the foam is reached. Suddenly, the walls begin to fail and the meringue takes on a broken appearance similar to dull, lumpy clouds. The addition of acid (in most cases, cream of tartar) helps strengthen the bonds between proteins, while sugar adds viscosity to the water, both of which make for stronger bubbles and prevent this lumpiness from occurring.
What does all this mean to you, the cook? When making meringue, vigilance is key, which means watching the egg whites carefully as they whip, adding the other ingredients at the proper times, and adding the sugar steadily and in small amounts, to ensure that you are stabilizing the meringue while the sugar to dissolves properly into the mixture. Cooks use all sorts of different approaches when making a French meringue, none of which are wrong, but I've found that the one I demonstrate here yields a reliably stable meringue with just a few steps.
Once you've mastered the French meringue technique, be sure to click over to this recipe for truly amazing, super-chocolate bomb, gluten-free chocolate chip meringue cookies.