The Science of Cooking
an Egg
WHAT'S IN AN EGG?
For only 70 calories each, eggs are rich in nutrients. They contain, in varying amounts, almost
every essential vitamin and mineral needed by humans as well as several other beneficial food
components. Egg protein is the standard by which other protein sources are measured. A large
egg contains over six grams of protein. A large egg has 4.5 grams of fat, only 7% of the daily
value. Only one-third (1.5) grams is saturated fat and 2 grams are mono-unsaturated fat.
Egg Nutrition Facts Panel - Large Egg
HOW TO TELL IF AN EGG IS FRESH?
As eggs age, carbon dioxide that was dissolved in the egg whites seeps out through the pores in
the shell, and oxygen gas seep in- the loss of CO2 makes the egg more alkaline and a lore likely
place for bacteria to grow. The older the egg the more air has seeped in.
How to tell the freshness:
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Place the egg in a bowl of tap water.
If the egg lies flat on the bottom- it has a small air cell and is fresh.
If the egg bobs up and down on the bottom – it has a larger air cell and not as fresh.
If egg floats to the surface – egg may be rotten.
Crack an egg onto a plate- it the egg white is thick and doesn’t spread- it is fresh.
PROTEIN IN EGGS
Egg yolks and egg whites are high in protein. The proteins change from liquid to solid as they
cook.
In an uncooked egg- the protein strands are separate- they are tightly wound up. They let light
pass through them- you can see this in an uncooked egg. Raw chicken, shrimp and fish have this
protein characteristic about them as well.
When proteins are heated, the bonds across their springs break and the proteins unwind. The
proteins straighten out, with their bonds sticking out to the sides. The protein has changed from
its natural form and now is called a denatured protein.
Almost immediately, this denatured (unwound) protein with its bond sticking out runs into
another and they link together to form a delicate three- dimensional mesh. There is no longer
room for light to pass through the proteins and the egg white becomes a solid white gel.
The longer and higher heat you expose proteins to, the tighter the bonds of the proteins mesh
becomes, squeezing out the water. Tender, moist, juicy proteins become dry and leathery. This
is why gentle heating is the real secret to cooking proteins- whether it is eggs or meat.
COOKING AN EGG
Test your knowledge about eggs by frying one and watching the science happen right before
your eyes!
Step 1: Sunny-Side Up
For sunny-side-up eggs, start with a hot nonstick skillet on medium heat. Swirl in a little butter.
Tip: Olive oil or bacon drippings will work great, too.
Step 2: Crack the Eggs
Crack the eggs into individual bowls. This way you can inspect for broken shells, yolks and
make sure the egg is fresh.
Step 3: Add the Egg to the Pan
Add the egg to the pan.
Step 4: Cover When the Edges Turn White
In about a minute, the outer edges will turn opaque. What is happening to the proteins? This is
your cue to cover the pan and lower the heat. Tip: A lid traps the steam and gently cooks the top.
Step 5: They're Ready
Wait 4 minutes and you'll have perfect eggs — no sticking or breaking. The longer you cook the
eggs, the harder the yolk will be. If you want a medium yolk, cook for 5 minutes. A hard yolk
will set in 6. Tip: Fresher eggs are best since the whites are firm and hold their shape better. Hit
them with salt and pepper to taste and that's it!
What are other ways to cook an Egg?
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Poach and Egg
Egg in a basket
Baked Egg