Recess4GrownUps

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Inside This Fragile Shell

The Science of Scrambled, Poached and Sunny Side Up

Eggs. First maligned, then idolized, and finally more or less dismissed as last year’s fad by professional nutritionists. Avian reproductive vehicle, delicious breakfast item, or prankster’s weapon, there’s a lot of science contained in that fragile shell.

Scrambled, fried, over easy, poached, sunny side up, hard boiled, soft boiled, in an omelet, over medium, raw…There is certainly more than one way to eat an egg. But what is it about eggs that makes them so versatile?

The answer lies in the balance of fats and proteins between the yolk and the white. Heating an egg introduces energy into the “system” - in this case, the egg. Agitated by the extra energy, the egg’s protein molecules begin to bounce around, bumping into each other and the surface of the pan in the process. Protein molecules naturally “fold” onto themselves, and they hold a shape unique to the molecular composition of that specific protein.

The impact of all the bouncing around causes the proteins to begin “unfolding”. As they unfold, they begin to bond with surrounding molecules, causing the egg to solidify. This keeps happening as long as the egg is on heat, so cooking too long allows too many bonds to form, and the egg comes out rubbery.

Picture: Creative Commons |Eggs

By introducing heat to a cracked egg flat in a pan, you can make over easy, over medium, or sunny side up eggs; by heating an egg still in its shell, you can make a hard-boiled egg.

Beating an egg does much the same thing to those folded-up proteins. Fat molecules don’t fluff up very well, so we separate the fat-free white from the yolk to make things like souffles and meringues. The force of the whisk or fork in the egg white introduces air bubbles, and makes those proteins bump into things and unfold just as they do when heated.

When you heat a beaten egg, the air bubbles expand, at the same time as the protein molecules solidify their bonds to one another under the heat. When you’re done, the air cools and leaves space surrounded by a network of solid egg proteins - giving you a self-supporting structure, like meringue.

If you over-beat your egg and put too much air in, the egg structure will be too fragile to support itself; likewise, if you didn’t introduce enough air, you won’t get air pockets of the right size expanding during cooking. This is why making a good fluffy meringue, that doesn’t either come out too heavy or else collapse in on itself, is so hard! (And by the way, the same idea of air bubbles inflating to get a fluffy texture also applies when whisking up your favorite scramble or omelet.)

One of my favorite ways to cook an egg is poaching it. At first glance this method seems like it shouldn’t work - dropping a raw egg into hot water?! A fool’s errand. But it does work, and here’s why. When you drop your egg into the water, its proteins are all in their base, folded-up state - the egg will sort of lazily spread itself out. The heat and motion of the water, though, begin acting on those folded-up proteins, which are only loosely held together at first.

After a few minutes of abuse by those energetic water molecules, the proteins unfold…bond to their neighbors…and suddenly, that ephemeral egg white drifting in the water will snap to attention, drawing in around the yolk! The longer you leave the egg in the water, the firmer both the yolk and the white will become, as more and more of their proteins unfold themselves and become more tightly bonded to their neighboring proteins.

But as we all know, the most important question still remains to be answered…Which DID come first, the chicken or the egg?