Sunday, October 14, 2012

How Long to Boil an Egg

Water boils at 212°F. You probably already knew that. But, that's only true at sea level. The boiling point of water changes with pressure, and there is less pressure at higher altitudes. So, at the lowest point in Colorado (3,317 feet) water boils at about 205°F.

The other interesting thing about boiling water is that it never gets hotter than its boiling point. As heat is pumped into the water, the hot water turns to steam and boils off. The remaining water sits happily at the boiling point.

Remember, though, that the boiling point of water changes with the pressure. So, if you put a lid on the pot, the steam fills the space in the pot, the pressure goes up and so does the water temperature. It doesn't go up by much because the pressure releases as soon as it is high enough to push past the weight of the lid.

All that is by way of introducing an experiment Gail and I did on how long you need to boil an egg to reach different degrees of firmness. You might be familiar with the 3 minute, or soft boiled egg. They are cooked just enough to whack open with a knife and eat with a spoon. It's the sunny-side-up of the boiled egg world.

On the light side of the boiled egg world is the coddled egg. A coddled egg is boiled for 1 minute to both slightly firm up the whites and to disinfect the outer shell. Coddled eggs get used in Caesar salad dressing or to prep an egg for better poaching.

On the other side of the boiled egg world is the hard boiled egg. There are two ways to hard boil eggs. One is to boil the heck out of them for 15 to 20 minutes. The other is to put the eggs in cold water, then bring the water to a boil. When the water is boiling, cover the pot and turn off the heat. In two hours, the eggs will be perfectly boiled and cool enough to handle.

We were looking for the perfect egg for the center of a Scotch egg. We want them firm enough to peel, but runny enough to add some moisture to the dish. So we test boiled eggs for various lengths of time. Here are the results:

3 minutes
    1/4" of soft cooked whites with some remaining runny
    completely runny yolk
    not possible to peel

4 minutes
    fully firm whites
    yolk starting to firm, but still runny
    hard to cut open like a soft boiled egg
    might be possible to peel with patience and luck

5 minutes
    fully firm whites
    1/4" firm yolk, with runny center
    can be peeled with care

6 minutes
    fully firm whites
    1/4"+ firm yolk, with runny center
    easy to peel

7 minutes
    fully firm whites
    1/8" firm yolk, with runny center
    can be peeled with care

8 minutes
    fully firm white
    mostly cooked yolk, with 1/4" soft yolk center
    easy to peel

9 minutes
    fully firm white
    mostly cooked yolk, with 1/8" soft yolk center
    easy to peel

Note that the 7 minute egg seems much like the 5 minute egg. We switched to a new batch of eggs at 7 minutes. The new eggs were slightly larger and a bit fresher. This happy accident points out that you can't perfectly time how done an egg will be. If you need a specific level of cooking, you might do a test egg at 6 minutes and use the table above to predict the result you are looking for.

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