Separate eggs immediately after taking them out of the refrigerator (cold eggs separate more easily). Separate the egg whites from the yolks and allow them to stand at room temperature for 30 minutes -- this will allow the egg whites to reach their full volume when beat. (Refrigerate the yolks for another use.) Carefully separate each egg white into a small bowl, such as a custard cup. If any yolk gets into the egg white during separation, refrigerate that white for another use -- even the tiniest bit of yolk can inhibit the beating quality of the whites. Transfer each egg white to an extra-large glass bowl . The bowl should be perfectly clean and wide enough to keep the beaters from being buried in the egg whites as they fluff. Do not use a plastic bowl, which may have an oily residue that can minimize the volume of beaten egg whites.
For food safety reasons, do not let the whites stand at room temperature for longer than 30 minutes.
Beat the egg whites, cream of tartar, and vanilla on medium to high speed until soft peaks (tips of the egg whites will curl when beaters are lifted). form. The cream of tartar stabilizes the egg whites and produces a whiter cake.
Gradually add the granulated sugar, about 2 tablespoons at a time, to allow the sugar to dissolve completely in the egg white mixture. Beat at medium to high speed until stiff peaks (tips of the egg whites stand straight up) form.
Do not overbeat or underbeat egg whites -- they should be stiff but not dry or your cake may fall.
Fold the sifted flour mixture, one-fourth at a time, into the egg whites. To fold:
Do not overmix, which can decrease the volume of the batter and result in a tough cake.
For a fine, even cake texture, eliminate large air bubbles by gently cutting through batter (in the pan) with a thin metal spatula.
Bake angel food cake in a preheated oven according to recipe directions. The cake is done when it turns a golden color and springs back when lightly touched. Cool angel food cake upside down (in the pan) to set.