How Do You Make a Perfect Boiled Egg?

Last Updated (Tuesday, 15 February 2011 15:49) Written by Raymond Nakamura

My Dad was telling me about the challenges of boiling and peeling an egg for my mother every morning. Never mind the concerns about cholesterol, or the Lilliputian feud over which end you should eat from, the more profound question that came up was why the shell SOMETIMES sticks when you try to peel it. I decided to eggs-amine this sticky question further.

Don't Be Fresh

The most common explanation I came across for reluctant eggshells was that the egg was too fresh. An egg has a membrane surrounding the albumin and another one lining the shell. The gas pocket in the wide end of the egg forms between these two membranes and gets bigger as the egg ages. This may help the membranes separate from each other, making the shell easier to peel.

Back to Basics

Connected to the physical effects of gas exchange, you have chemical changes of pH. The shell of an egg is mostly calcium carbonate, which has a high pH. The albumin (white) of a freshly laid egg is lower, between 7.6 and 7.9. It contains a lot of carbon dioxide, which forms a weak acid. As the egg ages, the carbon dioxide leaks out through pores in the shell and the pH goes up to about 9.2. Maybe equalizing the pH makes the membranes less attracted to each other.

Get Cooking

An egg gets from a chicken's cloaca to the supermarket shelf in about two to three days. Apparently they are best when more than a week old. If you're the sort who doesn't buy groceries until you have nothing left in your fridge and you don't want to wait a few days for your boiled egg, perhaps some cooking methods will help.

Poking Holes in the Idea

Pricking a hole in the wider end with the gas pocket,  allows the gases to escape as things heat up, so the egg white doesn't end up with a flattened end, if that matters to you. Some think this also allows some water to enter between the shell and the membrane so it is easier to peel.

Starting Cold

An egg white is 90% water and 10% protein. Heating breaks the weak bonds that give proteins their shape and forms new bonds, resulting a coagulated network of proteins that can hang on to water. If you crank up the heat too high or for too long, the proteins form too many bonds and let go of the water molecules so you end up with a more rubbery egg. Suddenly adding heat could result more bonds at the surface, so the white might stick more to the shell than the rest of the white. Starting with cold water means the egg heats up more slowly and perhaps more evenly. I like steaming.

Something in the Water

Some people recommend adding salt or vinegar or baking soda, but I'm not sure how that would affect "peelability." Adding salt to the water raises the boiling point, so the water could get hotter, which might make it more likely to stick. It could also change the osmotic pressure, so maybe water would be less likely to be seeping in or other materials to be moving out, but I don't know if that would affect anything. Vinegar is an acid, so it might lower the pH of the shell, bringing it closer to the albumin of a fresh egg. Baking soda would raise the pH, but I don't know how that would help.

Taking the Plunge

Finally, the way you cool down the egg make have a part to play. If you leave the egg hot, it will keep cooking. When you plunge the egg into cold water, the outer parts will presumably cool down first. If you don't leave them in the cold water for long enough, then the temperature difference might mean the white does not hold together as well, so it may be harder to peel cleanly.

I know this has not been a very hard-boiled investigation and these eggs-planations I've poached might seem a little scrambled. So as a benediction, it would crack me up if you'd shell out some of your own eggs-periences. Ova and out. That's all, yolks.