EGG WHITE FOAM
The ability of the egg white to form voluminous foams when whisked is nothing new to most people. However, sometimes the foam will not form and we might wonder why. Are eggs bad or is it something else? Often, the reason for the debacle is that some amount of egg yolk has sneaked into the egg white. Egg yolk contains quite a lot of fat molecules that simply interfere with egg white foam formation, and we end up with a less voluminous foam. So - make sure you separate the whites and the yolks carefully!
Egg white foam or even whipped cream are both very fluffy and contain lots of tiny but fragile air pockets. For this reason, they have to be ADDED to other ingredients, not the other way round. If you pour a heavy batter ON beaten egg white foam, it will be smashed under the weight of the batter. Always add foams TO the other ingredients! And when mixing, use gentle folding not vigorous mixing, so you don't lose too much air.