Eggs: the basics

Harold McGee’s chapter on eggs (to which I’ve been glued the past few days because holy cow, eggs are amazing) begins with this tribute to the humble food: “An egg is the sun’s light refracted into life” (69). And yes, if you back up the food chain it really is–the hen feeds the egg, plants feed the hen, the sun feeds the plants. But also eggs are a pretty incredible food and it’s unsurprising that they inspire poetry.

Eggs have to be complete nutrition for the developing chick, and it turns out that makes them pretty awesome nutrition for people too. Packed with protein and monounsaturated fat (one of the good ones), it also delivers the essential fatty acid linoleic acid, lots of vitamins and minerals, and plant-derived antioxidants. And in spite of the bad rap for cholesterol, studies have not shown a link between moderate egg consumption and heart problems. Conclusion: eggs are both delicious and nutritious.

In addition to being great fuel and a source of necessary amino acids (the building blocks of proteins), the proteins in an egg play a big role in how they cook. If you think about it, eggs are pretty unique in that with the addition of just heat, they go from gloopy and liquid to very solid. Heating up most liquids doesn’t get you much other than a hot liquid–even milk, a similarly complex liquid, only forms a skin when heated. So what happens in the egg to bring about this change?

As usual, it’s all about proteins. Eggs contain a bunch of different kinds of protein with different roles: some are mostly for chick food, others play defensive roles in blocking digestion by hungry egg-eaters, fighting off bacteria, or binding vitamins so that predators can’t benefit from them. In the raw egg, most of these proteins are loners. They fold in on themselves and float around in the water-based egg material as individual proteins. They are held together in the bundled shape by a variety of weak bonds, including hydrogen bonds (positive-ish hydrogen is attracted to negative-ish oxygen and nitrogen), hydrophobic interactions (all of the parts that don’t like water do like to be together), and van der Waals forces (weak positive-negative interactions). I’m realizing that these protein interactions come up all the time, so look out for a post all about bond! Coming soon to a blog near you.

Whether or not you care about what’s keeping the proteins all curled up on themselves, that’s where they are before cooking starts. When you add heat, things speed up: the proteins move around more quickly and bump into each other at higher and higher speeds. As anyone who’s played bumper cars with aggressive siblings knows, ramming into things at high speed knocks things around a bit, and in this case it disrupts those weak bonds holding the proteins in their folded-up shapes. They start to unwind into long chains, and now they form new bonds, this time with other proteins. Instead of individual balls of protein swimming in a lot of water, these new interactions form a kind of 3D web of connected proteins that holds small, isolated pockets of water. And voila, we have a solid.

The conditions of cooking the eggs and what else you add to them have a big effect on what happens, but this is the basic process. For less firm egg dishes like custards or eggnog, adding more liquid dilutes the proteins and makes the network less solid. On a smaller scale, adding a bit of milk to scrambled eggs dilutes the protein network just a little bit, giving you a more tender product. In the recipe below, I add yogurt, which both dilutes and adds acid into the mix, which also helps keep the eggs tender. But more on the chemistry of that another time–let’s eat already!

Broccoli-Tomato Omelet

I made this along with some breakfast potatoes for a delicious dinner. I started the onions and garlic for the omelet filling and potatoes at the same time, then took out half to save for the potatoes and continued as below for the omelet filling.

Yield: 2 omelets

1/2 onion

1/4 lb. broccoli (about 1 small head)

3 cloves garlic

1 T. olive oil

1/2 tomato

Salt

Pepper

Oregano

Thyme

6 eggs

1 1/2 T. plain yogurt

1 T. butter

Make the vegetable filling: chop the onion, broccoli, and tomato, and mince the garlic. Saute the onion in the olive oil until translucent, then add the garlic and cook until both are starting to brown.

Add the chopped broccoli and tomato, and the spices. Add 1/4 c. water to the pan and cover, let steam on medium heat for about 5 minutes. When the broccoli is almost soft, remove the cover and continue heating until the water is fully evaporated.

Make the omelets: beat the eggs and yogurt with a fork or whisk in a small bowl. Heat half of the butter in a pan until it starts to bubble but before it starts to brown. Add half of the egg mixture and tilt the pan so that it covers the entire surface. Allow to cook on medium heat for about a minute. When a skin has formed on the bottom, lift up an edge with a spatula to allow some of the liquid on top to flow underneath. When the top is almost set but still soft, add the broccoli and tomato filling in a line down the middle of the egg and fold both sides over. Repeat for the other omelet. Try to wait until the second one is done to scarf the first.