If you use fire when cooking eggs, it is easy to cause the air in the eggshell to expand rapidly, which will lead to the eggshell bursting. If you use a small fire, it will prolong the cooking time of eggs, and it is not easy to grasp the tenderness of eggs. Therefore, medium fire is most suitable for boiling eggs. If the egg is boiled in boiling water for too long, a series of chemical changes will occur inside the egg, thus reducing the nutritional value of the egg.