Making the perfect hard boiled egg is a bit of an art form. If you don't cook the egg long enough, the yolk will be too runny. However, if you cook the egg too long, the egg white will be tough. Even directions from cookbooks vary greatly. One you know the right directions to hard boil eggs, you'll be able to cook a great egg every time.
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When to Put the Egg in the Water
One of the biggest debates in making hard boiled eggs is when to put the egg in the water--before you boil the water or after the water has started boiling.
The big problem is that the ideal temperature for cooking an egg white is is 180 degrees and the ideal temperature for egg yolks is 158 degrees. The outside of the egg will heat up faster in the water, but if it gets too hot and you cook it for too long, it will become inedible.
Dropping the egg in the water as it boils heats up the egg unevenly. The outside becomes hot much too fast. Because of this, it's best to put the egg in your pan before you start cooking it.
How Long to Cook
Heat the egg up in the pan of water, then remove the pan from its heat source, allowing the egg to cook in the warm water. This lets you cook the egg without the overheating it. Once you've brought the water to a simmer, cover the pan and remove it from the heat source and allow the egg to sit for 10 minutes.
Amount of Water
If your pan is large enough to hold a lot of water, the water will still be quite hot after 10 minutes, causing the eggs to be overcooked. You should choose a pan that's the correct size for hard boiling an egg.
If you're just cooking one egg, choose a pan that allows you to have about 1.5 quarts of water in the pan. If you are cooking several eggs, you can judge the correct amount of water by covering the eggs with about two to three inches of water.