1, soak.
Before cooking eggs, it is best to put the eggs into cold water to soak for a while, the water must be no more than the eggs, otherwise soak the water where the protein is not easy to coagulate, affecting the digestion; and then put the eggs into cold water for a while, in order to reduce the air pressure inside the egg; and then put into the cold water pot boiling, so that the eggshell is not easy to rupture. Of course, this is only one of the ways to keep the shape of the egg intact.
2, fire.
Boiled eggs if the fire, easy to cause rapid expansion of air in the eggshell and lead to eggshell cracking; if the use of small fire, and prolonged the time to cook the eggs, and it is not easy to grasp the degree of good eggs old and tender. Practice has proved that boiled eggs to medium heat is most suitable.
3, time.
After determining the size of the fire, as long as accurately mastered the time to cook eggs, you can control the degree of tenderness of the egg at will. For example, soft boiled eggs, boiling water can be cooked for 3 minutes. At this time, the egg white solidified, the yolk is still fluid; cook loose eggs, boil the water and cook for 5 minutes. At this time the egg white solidified, the yolk was thick liquid, soft and smooth; hard-boiled eggs, boil the water and cook for 7 minutes. At this time the egg white solidified, yolk dry. It should be noted that, hard-boiled eggs, do not arbitrarily extend the time. Because the eggs in boiling water cooking time is too long, more than 10 minutes, the eggs will occur within a series of chemical changes, thus reducing the nutritional value of eggs.
4, in the process of cooking, in order to make the egg yolk solidified in the middle of the egg white, should be in the egg in the pot with a hand spoon constantly stirring in one direction, so that the water in the pot was swirling, until cooked. As for what principle this is, I think it must have something to do with centrifugal force and centripetal force in physics