There are a few essential things to know about egg whites in baking that will make all the difference to success.
When stiffly beaten egg whites are called for in a recipe, over-beating will break them down and deflate them once they are added to the mixture, at which point it will appear curdled. The problem is that it can be extremely hard to tell when eggs have crossed the fine line between stiffly beaten and over-beaten. In recipes where it’s critical for the whites to reach very stiff peaks—when making ladyfingers, for example, the batter will not keep its shape when piped if the meringue is not stiff enough—it can be easy to over-beat.
Luckily, there is a reliable safeguard, which I discovered many years ago, that has made a huge difference to my baking life: cream of tartar. Cream of tartar (potassium acid tartrate) is a byproduct of wine production (and an essential ingredient in snickerdoodles). Adding the proper amount of cream of tartar will prevent overbeating of egg whites 100% of the time.
It is essential to weigh or measure the egg white (see above!) because too little or too much cream of tartar will not protect the whites effectively. The ideal amount is...
Measure the cream of tartar by dipping the measuring spoon into the container and leveling it off with a metal spatula or knife. Be sure to wipe the outside bottom of the spoon with your finger before adding the cream of tartar to the whites, as some may have stuck to it.
When using an electric mixer, add the cream of tartar before beginning to beat. Start on low speed (or medium-low if using a small amount of egg white) and gradually bring the speed up to medium-high. If whisking by hand, wait until the egg white begins to foam before adding the cream of tartar.
If not using cream of tartar, it is advisable to beat the whites only to almost stiff peaks to avoid the risk of over-beating: They should curve slightly when the whisk is lifted out of the meringue. The French refer to this stage as bec d’oiseau, which means bird’s beak.
Some people prefer beating cold egg whites because, though it decreases the volume slightly, the meringue will be somewhat more stable. This isn't an issue if using the cream of tartar, so I prefer to allow the egg whites to come to room temperature to take advantage of the increased volume.
Pasteurized egg white that is sold in refrigerated containers in supermarkets has added acid to enable it to beat well.
Egg white from eggs pasteurized in the shell (such as from Safest Choice Pasteurized Eggs makes an exceptionally stable meringue (the process of pasteurization involves heating the eggs in the shell, and heat creates a more stable meringue, as in Italian or Swiss meringue) but requires double the cream of tartar and extra beating time on high speed.
Most bakers end up with lots of extra egg whites, so it’s useful to know that they can be frozen for months and, in my experience, without any loss of quality. I freeze egg whites in plastic containers—absolutely free of grease—with airtight lids.
To defrost, allow the frozen whites to sit overnight in the refrigerator, or set the container in a bowl of hot water. When thawed, lightly whisk for uniform consistency.
What's your biggest challenge in baking with egg whites? Tell us in the comments below (and maybe we can help!).