Eggs can provide balanced nutrition such as protein, fat, minerals, and vitamins, so they are sometimes called a "treasure trove of human nutrition". However, during storage, transportation, and other processes, eggs are affected by factors like temperature, humidity, and time, which can cause some eggs to spoil and become inedible. Especially the following types of eggs.
Smelly eggs: Due to bacterial invasion and massive reproduction inside the egg, it becomes spoiled. The eggshell turns a dark gray, and may even rupture due to expansion from internal hydrogen sulfide gas. The contents inside the egg will be gray-green or dark yellow with a foul odor. This egg must not be eaten, as it can cause bacterial food poisoning.
Cracked eggs: During transportation, storage, and packaging, eggs can develop cracks or fractures due to vibration, squeezing, and other reasons. This makes them very susceptible to bacterial invasion. If they have been stored for a long time, they should not be eaten.
Dead embryo eggs: These are eggs where the embryo's development has stopped due to contamination by bacteria or parasites, combined with poor temperature and humidity conditions during incubation. The nutritional content of this type of egg has changed. If the death occurred a long time ago, the protein will decompose and produce various toxic substances, so it is not suitable for consumption.
Moldy eggs: If eggs are rained on or become damp, the protective film on the surface of the eggshell can be washed away, allowing bacteria to enter and cause the egg to spoil and become moldy. This results in black spots and mold on the shell. This type of egg should not be purchased or eaten. In addition, eggs like "leaking yolk" eggs and "blood streak" eggs should generally not be purchased or consumed either.
Broken yolk eggs: This can be caused by mechanical breakage of the yolk membrane due to violent shaking during transportation, or by bacteria or mold entering the egg through the shell's pores over a long storage period, which damages the protein structure. The egg liquid will be thin and cloudy. If the yolk is not severely broken and there is no odor, it can still be eaten after high-heat treatment like frying or boiling. However, if bacteria have multiplied inside the egg, the protein has denatured, and there is a foul smell, it must not be eaten.