When the wind blows at the beach you're sure to see a lot of foam on the water's surface, called spume. Nothing more than bubbles reinforced with a lot of protein. Why do we mention that here, you ask? Because it is basically the same thing that rises to the surface of your simmering stock (called scum in the stock world). It has got to go. Use a ladle or fine wire mesh strainer to skim it off; you'll have a clearer stock. Make sure to rinse your skimmer between scoops.