Eggs lose moisture through their porous shells so become less viscous and more watery with age. The older the egg the flatter the egg yolk and the thinner the egg white.To test the freshness of an egg in it’s shell, float it in water. If it floats on it’s side it is very fresh, if it floats rounded end up it is a couple of weeks old, but an egg that floats right on the surface of the water could be several weeks old and so should not be used. Very fresh eggs are ideal for poaching. Eggs a few days old are ideal for whisking egg whites to make mousses and meringue mixtures.