Making a perfect hard-boiled egg might be a little but harder than you think. Either the yolk will be too dry or the eggs will stick to the shell so much that it will be really tricky to peel it.
The thing is that an egg consist of two different substances. Although it may seem strange for
you, the appropriate temperature for the white (to make a perfect hard-boiled egg) is 82 degrees
C and 77 degrees C for the yolk.
This principle was examined by J. Kenji López-Alt, an American cook who trusted science to find a way to make a perfect hard-boiled egg. He put a few eggs into boiling water for 30 seconds, then added a few ice cubes to reduce the temperature. Every 30 seconds he took out one egg and the effect can be seen below.