Eggs can be the source of some superb meals, but they can also be the source of food poisoning if they are eaten when they've gone bad. How do you tell when an egg is fresh or if it has gone bad, without cracking it open to find out -
Place the egg into a bowl of water. The water level should be deeper than the egg's length.
Observe what the egg does.
Fresh eggs will sink to the bottom of the bowl and lie on their sides.
Slightly older eggs (about one week) will lie on the bottom but bob slightly.
If the egg balances on its smallest end, with the large end reaching for the sky, it's probably around three weeks old.
Eggs that float at the surface are bad and should not be consumed.
Crack the egg open and look carefully.
Blood spots (also referred to as "meat" spots) don't signify a bad or fertilized egg. It's caused by a ruptured blood vessel during the formation of the egg. Since blood spots are diluted as the egg ages, their presence actually means you have a fresh egg. You can eat it safely, or remove the blood spot with the tip of a knife, if it makes you feel better.
Stringy, rope-like strands of egg white are chalazae which are present in every egg to keep the yolk centered. They're not a sign that the egg is bad or fertilized, and they can be consumed safely or removed.
An egg white that is cloudy or has a yellow or greenish cast to it is caused by carbon dioxide not having had enough time to escape from the shell and is especially common in fresh eggs.
Smell the egg. With time, bacteria break down the proteins in the whites of the egg and create a gas. This gas is called hydrogen sulfide, better known as "rotten egg gas."