Eggs are the perfect food, as they’re perfect for breakfast, lunch, dinner, and all things in between. But what is the science behind eggs? Let’s find out!
Few ingredients in the kitchen are quite as versatile as the egg. For the palate, eggs provide flavor, richness, structure and texture to a dish. For a recipe, eggs emulsify, provide moisture and leaven our food.
How can one little oval ovum do so much? Well, to understand how eggs do what they do, we must first stop thinking of the egg as one ingredient, but rather the sum of many ingredients that happen to share the same space.
To illustrate this point, I borrowed some colored pencils and a sheet of scrap paper from the Sons’ supply. While this isn’t the first time I’ve subjected my Friends to my feeble drawing attempts on the blog, those of you with any actual illustration talent may wish to divert your eyes for a moment.
Parts is Parts: How Each Part of the Egg Works
For our purposes, I’ll use a common chicken egg as the example, however the same principles apply to eggs of other fowl. (I can’t speak for the eggs of monotremes.) A chicken egg is designed to sustain the life of a chick through the incubation period as its food source.
The many parts comprising eggs serve a variety of functions with the goal of nourishing the budding chick:
The Yolk contains the most nutrients and serves as the primary food source. Don’t let the size fool you! That little yolk is packed with vitamins, minerals, protein, and all the fats that a growing chick needs.
The Albumen (a.k.a. egg white) serves to cushion the embryo and provide additional nutrition for growth. The albumen is primarily comprised of water, protein, and a few vitamins and minerals.
The Chalazae are fibrous cords that anchor the yolk to the poles of the egg to center the yolk. The chalazae are the chewy, spring-like white cords usually seen around the yolk when the egg is cracked open.
The Outer and Inner Membranes (a.k.a the shell and the skin lining the shell’s interior) are porous so as to allow the chick to breathe, yet the pores are small enough to protect it from a fair amount of bacteria from the outside.
These very same components of an egg can perform a variety of tasks in cooking based on the methods used and the desired results. When combined with other ingredients, eggs bind them together, add a great deal of moisture, and emulsify or thicken, depending on the method of incorporation.
Allow me to explain:
Let’s pretend that the photo above is the inside of a freshly laid chicken egg. The orange yarn represents strands of protein and fat globules. The white spaces around the strands are the water naturally present in the egg. The the strands of protein and fat globules are loosely swimming around in that water. When an egg is fresh, the strands of protein and fats keep pretty much to themselves, with their molecules remaining independent of each other as they float around.
When lightly agitated with a fork, the protein strands come closer together, strengthening their bonds. Agitation causes air to emulsify the the fat and water molecules with the proteins to form a gel. The gel acts as a basket which will trap and hold any other ingredients added, and provide structure in a recipe.
Without this structure, many baked goods–especially cakes and others with low gluten contents–would structurally collapse in the oven because the leavening alone isn’t sufficient to provide enough lift for a prolonged period in the oven.
Increasing the agitation incorporates more air and further strengthens the protein bonds in the gel basket, thus firming the overall structure. The more an egg is agitated, the stronger the overall structure. (As with scrambled eggs.) The inclusion of acid or heat also serve to strengthen the structure. (As with a quiche.) Incorporating more air will lighten the structure. (As with a meringue.) Adding additional moisture will loosen the structure, as it gets in between the bonds to push them further apart. (As with french toast batter or a custard.)
Classification of Eggs
The USDA classifies eggs by grade, size and color:
The Grade is determined by both the thickness of the shell and the weight of the albumen.
- Highest grade is Grade AA.
- Middle Grade A is the most commonly sold.
- Lowest is Grade B.
An egg’s Size is determined by weight of it’s contents, for which they are labeled and sold accordingly.
- Jumbo – 2.5 oz.
- Extra Large – 2.25 oz.
- Large – 2.0 oz.
- Medium – 1.75 oz.
Unless otherwise specified, all of the Comfortably Domestic recipes, and the majority of modern published cookbooks are developed using Large eggs. Substituting eggs of other sizes in a recipe can be done with consistent results, provided that the total equivalent weight is used. For example, if a recipe calls for 5 Large eggs, you may substitute 4 Jumbo eggs because both equal 10 ounces. Substituting different sized eggs based solely on number of eggs and not the total weight will alter the outcome of the recipe.
I don’t know about you, but calculating the percentage of ounces just to substitute egg sizes seems a lot like work, so I just stick to Large eggs.
The Color of an egg’s shell is determined by the breed of chicken that laid it, and does not affect taste or nutrition. Although based purely on aesthetics, the eggs from Araucana chickens are my favorite because they are such a pretty shade of blue.
Freshness of Eggs
Egg cartons in the US are marked with a “packed on” date, as well as a “sell by date.”
The Packed On date is usually located above the Sell By date, denoted by a number (01-365) corresponding with the day of the year on which it was packed. The Packed On date should be within a week of being laid, but legally can be packed within 30 days of being laid.
The Sell By date is the latest date that eggs may legally be sold. This is usually 30 days from the Packed On date.
USDA Guidelines state eggs are safe to eat three to five weeks after the Sell By date, if properly stored. Do the math and you’ll realize that equates to eggs that are over 3 months old.
Storage of Eggs
Eggs should be stored at 40°F. That cute little egg tray in the refrigerator door? Not the best place to store eggs because the temperature in the door averages 45°F.
The best place to store eggs in the refrigerator is on the top shelf, as it is usually between 38°F-40°F.
Storing eggs in a paper egg carton will help keep their porous shells from absorbing odors. Paper cartons slow down water evaporation from inside the egg that naturally occurs as it ages.
If you’re like me and have ever tossed a half wrapped onion next to the egg carton overnight, only to use a couple of those eggs the next day, and wound up with brownies that had an oniony undertone, then you know what I mean.
As eggs age, their over all structure begins to break down. I can totally relate. As a general rule,
- Fresh eggs are best for baking because they have the best structure, therefore lend the best structure to a baked good.
- Older eggs are better for hard boiling because their weakened structure also causes a weakened hold on the inside of the shell.
- An egg set out at room temperature for one day ages one week in terms of structural degradation.
Which Eggs are Best?
The superior egg in terms of taste and nutrition is a matter of intense debate. Personally, I like the least amount of miles between me and my food, so I prefer farm fresh organic because they’re from happy chickens! I know this because I have several friends that raise chickens, and the chickens are always smiling. 😉
Farm fresh and organic eggs have a bright yellow, sometimes orange yolk and a tight, clear egg white. Commercial varieties have a pale yellow yolk with a looser, runnier egg white.
What pasteurization does:
Pasteurized eggs are heated in their shells at temperatures high enough to kill most of the salmonella other harmful bacteria present, without being so hot as to cook the contents. How do you tell if an egg has been pasteurized? Well, the USDA mandates that an egg that has been pasteurized be coated with a thin layer of wax to seal the shell, and be stamped with the letter P.
Although Drs. James & R.W. Cox developed the early method of pasteurizing shell eggs, the method was further refined by L. John Davidson upon meeting the doctors. The current method of pasteurizing shell eggs in a controlled temperature bath is now patented. Pasteurized eggs in the United States are sold exclusively under the name Davidson’s Safest Choice.
What pasteurization doesn’t do:
Pasteurization does not sterilize the egg. In the United States, pasteurization kills around 80% of the harmful bacteria that causes food-borne illness from eggs.
Pasteurized Egg Products
Products such as Egg Beaters or other reduced fat/cholesterol egg products, are usually a blend of egg with emulsifers and coloring. As such, the USDA requires they be labeled as “egg products”. Egg products must be pasteurized after being removed from the their shells, prior to packaging.
Friends, there just is no substitute for an egg. No combination of ingredients can scientifically perform all of the wide variety of functions that an egg can accomplish to the same level. No substitute can provide the same richness and mouth feel as a real egg. That said, those allergic to them can take solace in the many ingredient combinations available that can be used as a pretty-darn-close-stand-in for the egg.
Click on the photos below for tantalizing recipes that apply egg science in different ways:
Fluffernutter Ice Cream by Country Cleaver