Many recipes call for egg yolks only, so you fill your refrigerator with a container of egg whites but, by the time you figure out what to do with them, they've gone bad. This is an easy technique for freezing egg whites.
When separating eggs, have an ice cube tray handy. Either separate the egg over the tray, letting the white fall into one compartment only of the tray. Or you can separate the egg over a small bowl and pour the egg white into the tray. Pour only one egg white into each compartment. This will work for small to large eggs. Jumbo egg whites might be too large for the compartments, but most recipes call for large eggs anyway.
Place the ice cube tray in the freezer and freeze the egg whites until firm. Pop the egg whites out and transfer them to a zip-top freezer bag and return to the freezer. Now, whenever you need one, two or three egg whites for an egg-white only recipe, you have them, premeasured, at your disposal. Just thaw as many cubes, representing one egg white each, as needed in the refrigerator and use.
Egg whites will deliver full volume if they are at room temperature. So, once the egg white is completely thawed in the fridge, let it come to room temperature before whipping. Recipes That Use Leftover Egg Whites.
Also take a look at how to freeze leftover egg yolks.