The Incredible Edible Egg!

Eggs a la Salvador

I crack an egg on the edge of my frying pan. The clear viscous liquid     and runny yellow yolk, that has already been broken, is dumped into a bowl. I    proceed to grab a metal fork and beat them loosely, until the entire concoction is about the same yellow color. It doesn’t take a lot. There is a piece of cracked shell in the mix, but I don’t mind. I pour the scrambled egg on to the frying pan, which has been on high heat for some time now. I mix the contents around on the frying pan so it cooks faster. Sure parts of the egg start turning brown, but that is the way I like it; plus, you can’t beat the smell. The brick of egg is flipped on to my plate: I sprinkle some salt, give it a squirt of ketchup, and off I go to devour   what I so proudly made.

Eggsactly how important are eggs?

Although cooking “eggs a la Salvador” may seem as a simple procedure, there is actually a lot of chemical processes going on when cooking eggs. Haven’t you ever wondered why egg whites are clear when raw, but turn white when cooked? Or why your eggs appear perfectly cooked in the pan, but are overcooked on the plate? The answers to these questions, and any others that you may have, are all based on chemical processes that occur.

Egg Structure and Importance of Protein

http://www.exploratorium.edu/cooking/eggs/images/eggcrosssection.gif

An egg can be thought of as spheres within spheres. The germ cell, or embryo, is located inside the yolk. The yolk is the yellow spherical glob that is found in the center of the egg. Its color is dependent on the combination of several different pigments and can vary from animal to animal. The yolk contains most of the nutrients and calories; so, it contains a lot of fats, proteins, vitamins, and minerals. This is necessary for the chick’s growth. The fat in the yolk plays a crucial role in why eggs are so useful in cooking (more on that in the future). The yolk membrane separates the egg yolk from the egg white.

The egg white has both thin white and thick white. They both serve as a barrier between the yolk and the hard shell. There are also chalazae, which are two think twisted strands that hold the yolk in the center of the egg. This keeps the yolk from hitting the hard surface of the egg shall. The egg white, or albumen, is made up of mostly water and protein. It contains very little vitamins and minerals. Three important albumen proteins are ovomucin, ovalbumin, and ovotransferrin. Ovomucin is what determines the quality of the egg both commercially and culinary: it makes up the thick egg white. Ovalbumin contains sulfur groups which contribute to the flavor, texture, and coloring of cooked eggs. Ovotransferrin holds the iron closer together, preventing bacteria from using them. Have you ever wondered why sometimes the yolks of hard-boiled eggs are yellow? It is all thanks to this protein holding the iron close to the yolk. Ovotransferrin determines at what temperature the eggs sets because it is the first protein to coagulate, darken in color and change in structure.

The color, texture, and flavor of cooked eggs depend on protein structure. Proteins are long chains of amino acids (primary structure) that are wound up together into helices and sheets (secondary structure). The tertiary and quaternary structures represent the complete protein with the amino acid contorted in a specific conformation. The structure of a protein is crucial to its function. Hydrogen bonds, ionic interactions, van der Waals forces, and disulfide bonds determine the specific configuration of the protein. When cooking, the heat denatures these proteins, breaking the bonds that are holding the specific configuration together. New hydrogen bonds and disulfide bonds form along the amino acid chain resulting in a different configuration. The configuration is also determined by ionic interactions between acidic and basic side chains of amino acids, as well as hydrophobic side chains. This new protein has different characteristics than the original protein before cooking. Before cooking an egg, the egg white is very clear and translucent. This is because the proteins are held together loosely, which allows light to pass through. As the egg white cooks however, it begins to turn opaque white. This is because the proteins have denatured and have coagulated resulting in a tighter protein network that blocks the light.

The proteins in the egg white can also be physically altered without heat, through physical agitation. When beating egg whites, the protein structure is physically being broken down. Like cooking, the protein structure will reform and create a new structure. These airy egg foams are perfectly described: they do in fact contain air. When the protein structure breaks apart, it allows air bubbles to get into the network of the structure. When the new structure is formed, the air bubbles are trapped in the actual protein network. Beating the albumen too long is detrimental to the stability of the foam: The proteins are packed so close together that the structure begins to collapse. A whisk is recommended when beating because they aerate a greater volume of egg at a time which will lead to less work for you.

Egg Fat

When making meringues during class, Professor Miller stressed the fact that the egg whites should be yolk free when beaten. The egg whites should not just be yolk free, but fat and oil free as well. The fat found in the egg yolk actually competes with the albumen proteins for space in the protein network. Fats do not have the structural capabilities to incorporate themselves in the protein network via bonding. They interfere with the proteins by physically getting in between them, preventing proteins from binding together. Since the fat prohibits proteins from binding to one another, the air bubbles are not able to be trapped within the structure. When beating egg whites it is sometimes recommended to use a metal bowl instead of a plastic bowl because plastic bowls are known to have traces of fat due to the hydrocarbon chains found in fats and plastics.

There is one thing fat does add to food, and that is flavor. Fats allow for a creamy texture and unparalleled smoothness. The effects from fat in the yolk can be found in eggnog, flan, and quiche. Egg-liquid mixtures are used to create custards and creams. Custards are made in the same container and cooked without stirring, resulting in a thicker more cohesive network. Creams are stirred during heating, which does not allow for a network to settle down. Creams may be on the malleable side, however. By adding cream, water, or milk to scrambled eggs, people are creating an egg-liquid mixture that results in the desired consistency and texture.

Eggsperiment #1: Scrambled Eggs

This experiment focuses on the effect that different additives have in scrambled eggs. There are three additive groups: 1% milk, heavy cream, and no additive. Each group will have two samples, one that is cooked properly and one that is overcooked. Each egg is scrambled before pouring on to a pan and one table spoon of additive is added. The results and experimental data can be seen in the table below.

Additive

Flame Setting (time changed)

Degree of Preparation

Time (min) Description
None 3 (1:20)4 Overcooked 2: 40
  • Immediately cooked
  • Very dry product
  • Rubbery texture
  • Brittle
None 2 Cooked properly 32 sec
  • It was not done when removed from heat, but cooked on the plate
  • Moist
1% Milk 3 (1:15)4 Overcooked 4:00
  • Browning was visible at 3 min 30 sec
  • Took longer to cook than no additive
  • Can hear the water sizzling on the pan (water is evaporating)
1% Milk 2 Cooked properly 1: 04
  • Took longer to cook than no additive: the milk adds water and volume spreading out the protein
  • Moist
Heavy Cream 3 (1:20)4 Overcooked 4:00
  • Browning at 2 min (due to lactose)
  • Fluffier
  • Tender
Heavy Cream 2 Cooked properly 1:00
  • Very moist
  • Very fluffy and tender

Back to Eggs a la Salvador

So maybe eggs a la Salvador are not your ideal version of scrambled eggs. There are many things can be critiqued in the cooking method. First of all, it is recommended that when cracking an egg, one should use a flat surface rather than the edge of a cup or a frying pan. This method reduces the chance that any piece of cracked egg shell will fall into the egg.

Eggs a la Salvador call for beating the egg loosely until the color is yellow, which does not take much. Beating the egg thoroughly helps in denaturing the proteins when cooking. This also helps in trapping not only air, but water within the protein network. Pouring the scrambled egg on to a very hot frying pan is not recommended either: sure it goes faster, but the egg turns tough and rubbery. The high heat forces the protein to quickly coagulate into a tighter network which squeezes more water out of the protein, which evaporates, making the egg texture more like rubber. This can be seen by the steam that is leaving the eggs during cooking. High heat can also start browning the eggs very fast. This is known as the Maillard reaction. The fat in the yolk is broken down to simpler sugars, which vary in flavor and aroma. The ideal scrambled eggs however, are an impressionist painting of white and yellow curds of different sizes. In order to cook moist tender scrambled eggs, slowly cooking them on low heat is the way to go.

Constantly moving and stirring the eggs around while cooking is recommended in order to achieve even curds of both yolk and albumen. If the scrambled eggs are left cooking for a while before disturbed, the proteins on the bottom layer will coagulate. This will lead to uneven sized curds because the proteins on top will not coagulate due to the uneven distribution of heat. There is also residual heat within the eggs, so even when the heat on the stove top is shut off, the eggs will continure to cook.  It is for this reason that it is suggested that the eggs should be removed from the pan while they are still underdone. Alton Brown said that if they are cooked in the pan, they will be overcooked on the table. The best method to cook scrambled eggs is over low heat with constant stirring. Once the eggs are a bit under cooked, appearing like they will almost be just right, they should be taken off the pan and placed onto a plate. It doesn’t matter whether this is your method of cooking eggs or not, to each their own. You may add cream, milk, anything you want; you might even it let it get a little toasty.

Eggsperiment #2: What happens when eggs are cooked at specific temperatures?

This experiment focuses on what is physically and chemically occurring inside an egg at different temperatures. A circulated water bath is used to cook the eggs at an exact temperature. A sample egg from each temperature studied is taken out, cracked open onto a small plate, and analyzed. The chart below shows what temperatures were used and a description of the egg.

Temperature of Circulator Description of egg
61 °C Neither the egg white nor yolk has shown a significant difference in opaqueness.
64 °C Thick white is settingThin white is also setting but to a lesser degreeGel like

Yolk also began to solidify

Yolk expanded

68 °C The whites have setThe yolk is relatively solidYolk holds its shape

Overall, the egg is a little bit more than soft boiled

75 °C Yolk is still getting more solidYolk can now break apart into separate solid pieces

I personally enjoyed the egg at 75 °C, but people have different preferences in how they like their eggs boiled. Another sample was going to be cooked at 85 °C, but we did not get to it. These different temperatures show how different parts of the egg solidify at different temperatures. It comes to no surprise that the whites solidified first because they have most of the protein. The yolk has a little bit of protein, but there are several other nutrients that would interfere with protein coagulation. Now, I’m not sure how many people have circulators in their kitchens, but Alton Brown shows us an alternative way to cook the perfect hardboiled egg. See the link below.

Alton Brown Chemistry of Eggs!

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3 responses to “The Incredible Edible Egg!

  1. Is there a chemical property about the yolk or the white that causes the yolk to form a perfect sphere every time is is cooked? Not all liquids, even those with membranes, form spheres within liquids of different densities. For example, red blood cells form “lozenge-shaped” discs in the blood serum. So, what is it about egg yolks which cause the perfect sphere?

  2. Are there any non-animal proteins that go from translucent to opaque when heated?

  3. Thanks a lot from Lurganure ;)

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