Do you ever wonder if the eggs in your refrigerator, or out in the chicken house, are still edible? Well, here is a simple test to determine the age of an egg. Fill a large drinking glass or tumbler with water and gently drop the egg in question, into the water. A fresh egg will drop to the bottom of the water and lie horizontally. As an egg ages the air cell in it grows causing it to float. Over time a fresh egg will no longer rest horizontally but it will begin to sit more vertical. If the egg is just slightly beginning to lift from one end, but is still staying at the bottom of the water, it is about one week old. An egg that is two to three weeks old will become obviously vertical but still remain at the bottom of the glass. When the egg has become too old to eat, it will float.
Notice the eggs in the photo. The egg that is floating is no longer edible. It has exceeded its shelf life. The egg on the bottom of the glass is very fresh and has a few more weeks to sit around the refrigerator.