As their name implies, poached eggs are cooked in water that is barely simmering. When cooked, the white should be just firm enough to enclose a yolk that is still soft. At the start of cooking, the water should be at a rolling boil, trapping the egg in the turbulence and shaping it to an oval; up to six eggs may be added at a time. Then the heat is lowered and the egg is poached until firm. The fresher the egg, the closer the white clings and the neater it will be after poaching; stale eggs are instantly detectable as the white detaches almost completely from the yolk, swirling out into the poaching water. A little vinegar in the water will help the whites cling, producing a neater egg. Special molded pans to immerse in the water are also available for poaching eggs, but these are spurned by serious cooks, as the egg itself is not surrounded by water.