It's been a few years since I've made one but the last time I made an
angel food cake was the last time I ate an angel food cake. The store
bought ones just can't compare. The trick is not to overbeat the egg
whites. If the whites are over whipped the cake will collapse in the
oven and you'll end up with a angel food pound cake. If you can turn
the bowl upside-down and the whites don't slide out then they're
ready. If you beat the eggs to the point where they start to lump and
look curdled then you've gone too far.