Key Temperatures in Cooking (part 2) - Eggs Begin to Set

2. 144°F / 62°C: Eggs Begin to Set

The lore of eggs is perhaps greater than that of any other food item, and more than one chef has gone on record judging others based on their ability—or inability—to cook an egg. Eggs are the wonder food of the kitchen—they have a light part, a dark part, and bind the culinary world together. Used in both savory and sweet foods, they act as binders holding together meatloaf and stuffing; as rising agents in soufflés, certain cakes, and cookies like meringues; and as emulsifiers in sauces like mayonnaise and hollandaise. Eggs provide structure to custards and body to ice creams. And all of this so far doesn’t even touch on their flavor or the simple joys of a perfectly cooked farm egg. Simply put, I cannot think of another ingredient whose absence would bring my cooking to a halt faster than the simple egg.

Egg whites are composed of dozens of different types of proteins, and each type of protein begins to denature at a different temperature. In their natural “native” state, you can think of the proteins as curled-up little balls. They take this shape because portions of the molecular structure are hydrophobic—the molecular arrangement of the atoms making up the protein is such that regions of the protein are electromagnetically repulsed by the polar charge of water.

Important temperatures in eggs.

Because of this aversion to water, the protein structure folds up on itself. As kinetic energy is added to the system—in the form of heat or mechanical energy (e.g., whipping egg whites)—the structure starts to unfold as kinetic energy overtakes potential energy. The unfolded proteins then get tangled together, “snagging” around other denatured proteins and coagulating to form a linked structure. This is why a raw egg white is liquid, but once cooked becomes solid. 

Hydrophobic proteins in their native state (left) remain curled up to avoid interacting with the surrounding liquid. Under heat, they denature (center) and uncurl as the kinetic energy exceeds the weaker level of energy generated by water molecules and regions of the proteins that repel each other. Once denatured and opened up, the hydrophobic parts of the protein that were previously unexposed can interact and bond with other proteins.

The most heat-sensitive protein is ovotransferrin, which begins to denature at around 144°F / 62°C. Another protein, ovalbumin, denatures at around 176°F / 80°C. These two proteins also are the most common in egg whites: ovotransferrin accounts for 12% of the proteins in an egg white and ovalbumin 54%. This explains the difference between soft-boiled and hard-boiled (“hard-cooked”) eggs. Get that egg up to about 176°F / 80°C for sufficient time, and voilà, the white is hard cooked; below that temperature, however, the ovalbumin proteins remain curled up, leaving the majority of the egg white in its “liquid” state.

Note:

Most of the proteins in egg yolks set at between 149°F / 65°C and 158°F / 70°C, although some set at lower temperatures.

Proteins in foods such as eggs don’t denature instantaneously once they reach denaturation temperature. This is an important point. Some cooking newbies have the mental model that cooking an egg or a piece of meat is something like melting an ice cube: all ice below a certain temperature, ice and water at the freezing/melting point, and all water above that temperature. From a practical perspective in the kitchen, it’s not an entirely incorrect picture, because heat pours into the foods so quickly that the subtle differences between a few degrees aren’t obvious. But as heat is transferred into the food more slowly, the subtleties of these chemical reactions become more noticeable. And unlike melting an ice cube, where increasing the heat transfer by a factor of two causes the ice to melt in half the time, cooking foods do not respond to additional energy in a linear fashion.

You might find it easiest to think of the different proteins in foods as having particular temperatures at which they denature, and try to shoot for a target temperature just above that of the proteins you do want denatured. Just remember: there’s more to a piece of meat or egg than one type of protein or connective tissue, and the different proteins have different temperature points at which they’re likely to denature.

Here are some examples of cooking eggs that show how to take advantage of the thermal properties of different portions of the egg.

2.1. Hard-Cooked Eggs, Shock and Awe Method

There’s a silent war of PC-versus-Mac proportions going on over the ideal way to make hard-cooked eggs. Should you start in cold water and bring the water up to a boil with the eggs in them, or should you drop the eggs into already boiling water? The cold-start approach yields eggs that taste better, while the boiling-water approach yields eggs that are easier to peel. But can you have both?

Thinking about the thermal gradient from shell to center of egg, it would make sense that cooking an egg starting in cold water would result in a more uniform doneness. The delta between the center and outer temperatures will be smaller, meaning that the outer portion won’t be as overcooked once the center is set compared to the boiling-water method.

The conjecture for ease of peeling in the boiling water approach is that the hot water “shocks” the outer portion of the egg. Into industrial-grade cooking? Steam ’em at 7.5 PSI over atmospheric pressure and quick-release the pressure at the end of cooking to crack the shell. (Hmm, I wonder if one could do this in a pressure cooker...) But what about the rest of us? What if we shock the outside, and then cook in cold water?

Try it. Place your eggs into rapidly boiling water. After 30 seconds, transfer the eggs to a second pot containing cold tap water, bring to a boil, and then simmer. The second-stage cooking time will take about two minutes less than the normal cold-start approach. Cook for 8 to 12 minutes, depending upon how well cooked you like your eggs.

2.2. The 30-Minute Scrambled Egg

This method involves ultra-low heat, continuous stirring, and a vigilant eye. I wouldn’t suggest this as an everyday recipe, because it takes a while to make, but after however many years of eating eggs, it’s nice to have them cooked a new way. Cooking the eggs over very low heat while continuously stirring breaks up the curds and allows for cooking the eggs to a point where they’re just cooked, giving them a flavor that can be described as cheese or cream-like. It’s really amazing, and while the thought of “cheese or cream-like” eggs might not have you racing off to the kitchen, it’s really worth a try!

In a bowl, crack two or three eggs and whisk thoroughly to combine the whites and yolks. Don’t add any salt or other seasonings; do this with just eggs. Transfer to a nonstick pan on a burner set to heat as low as possible.

Stir continuously with a silicone spatula, doing a “random walk” so that your spatula hits all parts of the pan. And low heat means really low heat: there’s no need for the pan to exceed 160°F / 71°C, because enough of the proteins in both the yolks and whites denature below that temperature and the proteins will weep some of their water as they get hotter. If your heat source is too hot, pull the pan off the stovetop for a minute to keep it from overheating. If you see any curds (lumps of scrambled eggs) forming, your pan is getting too hot.

Stir continuously to avoid hot spots so that the eggs are kept at a uniform temperature. If you have an IR thermometer, make sure your pan doesn’t exceed 160°F / 71°C.

Continue stirring until the eggs have set to a custard-like consistency. When I timed myself, this took about 20 minutes, but you might reach this point in as few as 15 minutes or upward of half an hour.

2.3. Oven-Poached Eggs

Here’s a simple way to cook eggs for a brunch or appetizer. In an individually sized oven-safe bowl (ideally, one that you can serve in), add:

Create a “well” in the center of the ingredients by pushing the food into a ring around the edges of the bowl. Crack two eggs into the well, add a pinch of salt and some fresh ground pepper, cover with aluminum foil, and bake in a preheated oven set to 350°F / 180°C until the egg is set, about 25 minutes. (You can use a probe thermometer set to beep at 140°F / 60°C.) Try adding some crushed red pepper flakes to the breakfast version or sriracha sauce to the dinner version.

2.4. Pasteurized Eggs

While salmonella is quite rare in uncooked eggs, with estimates being somewhere around 1 in 10,000 to 20,000 eggs carrying the bacteria, it does occur in the laying hen populations of North America. If you’re cracking a few dozen eggs into a bowl for an omelet brunch at your local hacker house every week, let’s just say that odds are you’ll eventually crack a bad egg. Luckily, this isn’t a problem if those eggs are properly cooked and cross-contamination is avoided.

The real risk for salmonella in eggs is in dishes that use undercooked eggs that are then served to at-risk populations (e.g., infants, pregnant women, elderly or immunocompromised people). If you’re making a dish that contains raw or undercooked eggs—Caesar salad, homemade eggnog, mayonnaise, raw cookie dough—and want to serve that dish somewhere where there might be at-risk individuals, you can pasteurize the eggs (assuming your local store doesn’t happen to carry pasteurized eggs, but most don’t). Pasteurized eggs do taste a little different, and the whites take longer to whip into a foam, so don’t expect them to be identical to their raw counterparts.

Since salmonella begins to die at a noticeable rate around 136°F / 58°C and the proteins in eggs don’t begin to denature until above 141°F / 61°C, you can pasteurize eggs to reduce the quantity of salmonella, should it be present, to an acceptable level by holding the egg at a temperature between these two points. The FDA requires a 10,000-fold reduction (5 log₁₀ in food safety lingo), which can be achieved by holding the egg at 141°F / 61°C for 3.5 minutes (according to Margaret McWilliams’s Foods: Experimental Perspectives, Fifth Edition, from Pearson Publishing). 

2.5. The 60-Minute Slow-Cooked Egg

Going back to our earlier discussion of time and temperature, when food is left in an environment long enough, its temperature will come to match that of its environment. Therefore, if we immerse an egg in water held at 145°F / 62.7°C, it follows that the proteins in the white and the yolk that denature at or below that temperature will denature and coagulate, and those that denature above that temperature will remain unaltered.

The added benefit of this method is that the egg cannot overcook. “Cooking” is effectively the occurrence of chemical reactions in the food at different temperature points, and holding the egg at 145°F / 62.7°C will not trigger any reactions that don’t occur until higher temperatures are reached. This is the fundamental concept of sous vide cooking.  For a sous vide–style cooked egg, immerse an egg in water that is maintained at 145°F / 62.7°C for one hour. As you’ll see, sous vide cooking has some incredible properties that greatly simplify the time and temperature rule.

Note:

Your average, run-of-the-mill (or is that run-of-the-yard?) chicken laid only 84 eggs per year a century ago. By the turn of the millennium, improvements in breeding and feed had pushed this number up to 292 eggs per year—almost 3.5 times more. And, no, science has not yet figured out which came first.