Knowing why eggs float can make a difference between enjoying a tasty meal and feeling ill. When boiling eggs, an egg that floats to the top of the pot can mean that the egg is old.
An egg becomes buoyant when its air cell enlarges significantly. According to the Benton Franklin Health District, once a hen has laid an egg, an air cell forms. As the egg ages, the cell grows larger. A large air cell will cause an egg to float to the top of a pot of boiling water.
Even if an egg floats, it may still be safe to eat.To ensure that it's not spoiled, crack the egg into a clean bowl and examine the contents for discoloration. If the egg is discolored or has a bad odor, you should not eat it.
Time and temperature affect the quality of an egg and whether it will float. As time passes, the quality of the yolk and egg white diminishes. To reduce the chances of having eggs that float when boiling them, refrigerate them; never leave eggs at room temperature for more than two hours.