Beating egg whites over a double boiler for increased leavening?
actually for egg yolks it does the heat help on that, for egg whites they should be at room temperature not cold because at room temperature reaches maximum volume faster than
cold egg whites, and the utensils used like the electric or hand mixer and bowl must not have any trace of grease because fat inhibits the raise process. with taking care of this you will get a good volume of the egg whites, also take into account that if the eggs whites contains sugar it will stabilize the egg foam,with this the meringe (yes now it has become a meringue is you gonna do that) wont go down after a long time, also depending in the manner that you made it either swiss,french, or italian way,if your recipe calls for that then do it, if not, dont.