1. Smell the egg. If it smells bad, it's probably rotten. Fresh eggs should have a mild, pleasant smell.
2. Look at the egg. If it has any cracks or holes in the shell, it's probably rotten. Bacteria can enter the egg through these cracks and spoil it.
3. Shake the egg. If you hear a sloshing sound, the egg is probably rotten. The yolk and white of a fresh egg should be thick and firm.
4. Candle the egg. Candling is a method of检查 eggs to see if they're rotten. To candle an egg, hold it in front of a bright light in a dark room. If the egg is rotten, you'll see a dark spot inside the shell.
5. Water test. Place the egg in a bowl of water. If the egg sinks to the bottom, it is fresh. If it floats, it has gone bad.
If you're not sure whether an egg is rotten, it's best to err on the side of caution and throw it out. Eating rotten eggs can cause food poisoning.