Hard-boiled madness

To make a good soft-boiled egg takes, what, between three and three-and-a-half minutes of boiling. Leave it for 30 seconds longer and the yolk is hard.

So why, pray tell, was I always told that to make a hard-boiled egg takes ten minutes of boiling? Grandparents and parents alike told me the same story: 10 minutes to hard boil. Where did this law come from? Surely five’s enough at an absolute maximum?

In fact, I’ve heard that all you actually need to do is bring the eggs to a full rolling boil for about a minute, cover with a tight fitting lid and turn the heat off. If left in this state for around ten minutes, the heat in the pan is enough to cook the eggs thoroughly without using precious energy.