A while back, I did an in depth posting on beating egg whites, but I have something important to add if not using cream of tartar to ensure stability.If the proper amount of cream of tartar is used it offers 100% insurance against over beating and drying out the egg whites, which would decrease the volume of the baked goods significantly. When using the cream of tartar, the egg whites can be beaten to stiff peaks. But when cream of tartar is not used, the egg whites should be beaten only until what the French refer to as bec d'oiseau which translates to bird's beak. By not beating quite as stiffly, when folded into another mixture the whites do not deflate as much but will not offer quite as much volume. An example, in my orange chiffon cake, is when the whites are beaten to completely stiff peaks only 9 egg whites are needed instead of 10 when beaten to bec d'oiseau (curved peaks) to achieve the same volume when baked.