Eggs contain methionine, and when cooked for too long, it will decompose to produce some sulfides, which will react with iron ions in eggs to form dark ferrous sulfide, which is the scientific explanation for the green appearance of egg yolk. In fact, this phenomenon is more common in salted duck eggs, and ferrous sulfide will also be formed in preserved eggs, just because the preserved eggs themselves are dark in color, which we can't notice.

Eating such eggs will not cause cancer. First of all, there is very little sulfide on the egg yolk, which may become hydrogen sulfide and ferrous chloride under the action of gastric acid. If it does not react with gastric acid, it is also a water-insoluble compound and will not participate in the metabolic process. Secondly, the sulfide on egg yolk does not affect protein digestion.

Finally, the process of human intestinal digestion is the process of microbial fermentation, and it is normal to produce metabolic wastes such as hydrogen sulfide and biogenic amines. The amount of hydrogen sulfide in the intestine far exceeds the water-insoluble ferrous sulfide on the egg yolk, so you can eat it safely.

Extended data:

Timing is very important for boiled eggs.

If the eggs are cooked for a long time, not only will they taste old and choke, but vitamin E will also be lost by about 16%. Therefore, boiled eggs must be just right, and it is best to cook them tender, giving consideration to taste and nutrition.

First, put the eggs in cold water, boil them with high fire, then keep them boiling for 3~5 minutes, turn off the fire, and stew the eggs with waste heat for a while, which usually takes about 8 minutes. The eggs cooked in this way are in the healthiest state, the egg white is tender, the yolk has just solidified, and it tastes fresh and not choking.

In addition, it is best not to eat half-cooked eggs. The yolk is in a "heart-warming" state, which indicates that sterilization is not complete, which will increase the risk of infection by pathogenic bacteria such as Salmonella. Therefore, we should control the time of boiling eggs at ordinary times. When the yolk is completely solidified, it will be no problem to eat.

People's Health Network-It is normal for the yolk of boiled eggs to be green, and boiled eggs have "golden 8 minutes"