Another thing to keep in mind is the freshness of your eggs. It turns out there's truth to the old saying "Fresh eggs are for frying and older eggs are for boiling." As Harold McGee notes in his book Keys to Good Cooking (Penguin, 2010), "Very fresh egg whites tend to stick to the inner shell and tear." To test eggs' freshness, drop them gently into a bowl of cold water. The freshest ones will immediately sink on their sides, while slightly older ones will tilt or even sit upright at the bottom of the bowl. Just be careful to avoid using eggs that float to the surface, a sign that they're past their prime.