The Accidental Scientist: Science of Cooking

recipe: Deviled Eggs
What’s Going On?

Why don’t I just let the eggs boil?

“A ‘boiled egg’ may be part of the breakfast tradition in many households, but boiling is a miserable way to treat an egg. Because high heat toughens protein, the major constituent of eggs, boiling quickly changes an egg from a tender gel to a resilient sphere.

“You might be surprised to learn that egg white solidifies between 140º F and 149º F—far below water’s boiling point. Egg yolk coagulates between 149º F and 158º F, a temperature higher than egg whites because the yolk's protein structure is different and not as sensitive to heat. When an egg is in boiling water, the intense heat promotes extensive protein bonding, so it solidifies quickly and changes to a texture that’s best described as ‘rubbery.’ Cooked gently, eggs are firm but still tender. They not only taste better, they’re easier to digest.”

—Anne Gardiner and Sue Wilson, The Inquisitive Cook

What happens when egg white cooks?

Egg-white proteins are long molecules, made up of chains of amino acids linked together. In a raw egg, these proteins are curled and folded to form a compact ball. When you cook an egg, these proteins uncurl and form new bonds with one another. The longer you heat the proteins and the higher the temperature, the tighter the proteins will bond to each other. The tightness of these bonds determines whether the eggs are cooked just right—or overcooked. Our method for hard cooking eggs heats the eggs slowly, making for loose bonds among the proteins and tender, rather than rubbery, egg whites.

How can I stop the yolk from turning green?

Plunging hard-cooked eggs into cold water helps keep the yolk from turning green. The green-gray color (and the whiff of sulfur smell that often accompanies it) comes from the reaction of iron in the egg yolk and sulfur in the egg white. When heated, the two can combine to make green-gray ferrous sulfide and hydrogen sulfide gas. To avoid getting a green yolk, cook your eggs just long enough to reach the desired doneness—no more. And quickly plunge the cooked eggs into cold water to stop the cooking process and minimize the iron-sulfur reaction.

Some people make a pinhole in an egg before they cook it. Why?

You may want to use a pin to poke a small hole in the large end of the egg before you boil it. The hole lets air escape from the air pocket at the large end of the egg, giving you a hard-cooked egg that is rounded, rather than flat, on the large end. Some say that water leaking in through this hole makes eggs easier to peel, but we haven’t noticed any difference in “peelability.”

Why are eggs sometimes hard to peel?

When an egg is very fresh, the cooked egg white may stick to the membranes inside the shell, making the egg difficult to peel. As an egg ages, the white becomes more alkaline and loosens its grip on the membrane. For the most peelable eggs, buy eggs a week to ten days before you hard cook them.

To make any egg easier to peel, crack the shell all over by rolling the egg between your hands. This breaks the shell into tiny pieces. It’s easier to get each tiny piece free of the white than to try to pull off a big chunk.


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