Enthusiastically but fleetingly. Put your ear to the foam and you’ll hear the bubbles popping. The other deficiency of the egg yolk is that its proteins are too stable. Neither the physical abuse of whipping nor the presence of air bubbles causes the yolk proteins to unfold and bond with each other into a reinforcing matrix. Of course heat will, as we know from hard-boiled yolks and custards. So supplement the yolk with liquid, and the whipping with careful cooking, and the mixture will rise to four or more times its original volume. Exactly this procedure is the principle of zabaglione and sabayon sauces.