The fundamental challenge of eggs

Eggs are tricky. Molly Birnbaum, executive editor of Cook's Science for America's Test Kitchen, agrees, and says it all comes down to the white and the yolk. She tells Sally Swift how to best soft-boil an egg and shares a recipe for Runny Yolk Sauce.

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Sally Swift: It's kind of deviled egg season, and I'm reminded how temperamental eggs are and how inconsistent they can be. I can do the same thing over and over and over, sometimes the shells don't come off, sometimes the yolk has a green ring. I mean, what is up with eggs?

Molly Birnbaum

Molly Birnbaum: That is an excellent question. Eggs are tricky. They're very, very tricky, and the fundamental challenge in cooking eggs is that an egg is not just one ingredient, but it's two ingredients in one: the white and the yolk. They both operate very differently when you're cooking with them.

The yolk itself starts to thicken at a different temperature than the white. The yolk starts to thicken at 150 degrees Fahrenheit and is fully set at 158 degrees Fahrenheit. So, it's a pretty small window of time there, whereas the white starts to thicken at 145 degrees Fahrenheit and is fully set at 180.

SS: Well, there's no way for us to win with that situation.

MB: There is no way to win. It's really hard to get exactly what you want, especially because you often want the white to be cooked and the yolk to be runny. it's a delicate balance getting it to the exact right point.

SS: What's the right way to soft-boil an egg?

MB: We've done a lot of experimenting, and we came up with a rather unique way of cooking soft-boiled eggs. It's tricky because you do need the firm whites and the still runny yolk, and oftentimes, because the white is on the outside, it cooks a little bit quicker. It's super tricky.

What we ended up doing is steaming the eggs, and this is because a big problem with soft-cooked eggs is keeping the water temperature and the resulting cook time correct. Every time you add or subtract an egg, or even use a different pan, that timing is thrown off, and even a one or two degree drop in temperature significantly influences the cooking time.

SS: Steam them in a steamer, like you would broccoli?

MB: Kind of. What we do is, we bring half an inch of water to a boil with a steamer in a pot and add eggs. You can add one egg, or you can add six eggs, and by steaming them, you can cook as many as you want and get them perfectly cooked each time. It takes about six and a half minutes.

SS: Rumor has it you've been working on a magical egg sauce, as well.

MB: You hear correctly. We are starting a new brand out of America's Test Kitchen called Cook's Science, and one of the first things that we did for Cook's Science is dive into the science of eggs and, specifically, the science of the yolks. We created a sauce that we're calling the "runny egg yolk sauce," which is exactly as it sounds.

It is that runny yolk from a fried egg or a poached egg, except it's isolated, and it's pasteurized, and you can keep it in your fridge and put it on anything that you want to.

SS: Ok, tell me how we do this perfect runny yolk sauce.

MB: It's very simple. You add egg yolks and salt together, and you cook it in a water bath in a Ziploc bag. This water bath can be done with a sous vide machine, which brings up the temperature of water to a certain temperature and keeps it there, or you can do it -- kind of hack -- in a cooler. You fill it halfway with boiling water, and then you add a little bit of cold water until the water in the cooler registers exactly the temperature that you want. Then you can kind of bring the temperature up or cool it down based on adding hot water or cold water.

SS: You have to babysit for 30 minutes while you're doing it.

MB: You do have to babysit for 30 minutes, but it's so worth it. My favorite thing to do with it is put it in a squeeze bottle and have it in the fridge. You could even use an old ketchup bottle that's empty and washed out, and then when you have a burger or a piece of pizza or a salad or pasta -- it's really good as kind of a makeshift carbonara -- you just spoon or drizzle a little bit of the sauce right in there, and it is so good.