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2.6: Eggs

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    What is an egg?

    There are many types of eggs and many animals that can lay them such as fish, birds, and amphibians but in this chapter we will be looking specifically at bird eggs. Bird eggs are laid by females and are incubated for a varying time based on species. A single young hatches from each egg. Hens lay eggs even when not fertilized and those are the eggs that we get from the store.

    The egg is made up of 5 Components going from the outside in:

    • Shell: Made up of calcium carbonate and acts as the the protection for the egg. It contains thousands of pores which allow gas to escape. Shell color is due to the type of hen and does not have any correlation with nutrient content. The shell accounts for about 12% of total egg weight.
    • Air cell: This is at the larger end of the egg, between the two shell membranes. This occurs because the inner contents of eggs contract after the egg is first laid due to their temperature dropping and allows this gap to form.
    • Albumen: this is commonly referred to as the egg white and contains mostly water and protein (majority of that protein is albumin). Egg whites also contain the protein avidin which when consumed raw can inhibit biotin absorption and in large amounts it can cause deficiency. While the albumen can appear as one homogenous fluid, it is actually separated out by different Viscosities. Egg whites account for about 58% of total egg weight.
    • Yolk membrane: This layer is made of up albumin and the vitelline membrane which help to keep the yolk contained.
    • Yolk: this is the bright yellow or orange center of the egg and contains most of the egg's nutrients. A white germinal disk can be seen attached to the yolk, however it appears much darker when fertilized. There are many lipoproteins in the yolk which make it a great emulsifying agent. The color and nutrients of the yolk are a direct result of diet and feed. The yolk accounts for 30% of total egg weight.
      • Chalazae: Located at the top and bottom of the egg, chalazae act as the anchor for the yolk which allow it to be suspended in the middle of the egg white. These appear opaque.
    Table 1.1 Egg Nutrients
    Nutrient Amount Per Large Egg Examples
    Protein 7 g (4g from white and 3g from yolk)
    • Albumin
    • Avidin
    Fat 5 g 
    • Triglycerides
    • Phospholipids
    • Cholesterol
    • Omega-3
    • Lecithin
    Cholesterol 213 mg ~
    Vitamins and Minerals ~
    • Fat soluble vitamins (ADEK)
    • B vitamins
    • Selenium
    • Iodine
    • Zinc
    • Iron

    Uses in cooking and in industry.

    Eggs are used for cooking in many different ways ranging from dressings to baked goods or even on their own. The table bellow explains some of the many functions and uses of eggs:

    Table 1.2 Functions of Eggs
    Functions Explanation Examples
    Emulsify The lipid lecithin is a natural Emulsifying agent found in egg yolks. This molecule is amphiphilic meaning it attracts both water and lipids because it contains both a Hydrophobic and hydrophilic section. This structure gives the yolk the ability to mix fats and water together and stabilizes them to reduce separation.
    • Salad dressings
    • Hollandaise
    • Bearnaise
    • Mayonnaise
    • Ice cream
    • Choux pastry
    Bind The protein in eggs allow them to be great binding agents. Many foods are not able to stick together on their own and egg is used because when the proteins are heated, they coagulate and create a food adhesive and will give stability and keep structure.
    • Meatballs
    • Breaded foods
    • Meatloaf
    • Lasagna
    • Manicotti
    Foam When air is beaten or incorporated into egg whites, they are very good at holding their shape and building foams due to the proteins. When air is being incorporated into egg whites, the proteins unwind and stretch to allow as much air as possible to get in and stay there. Acids can help this foaming ability and lipids inhibit it. The quality of the foam can also depend on temperature, age of the egg, the equipment, duration and other ingredients like salt/sugar.
    • Meringue
    • Souffle
    • Macaroons
    Interfere When making frozen desserts, egg yolks are used to inhibit the formation of large and grainy ice crystals to result in a smoother product.
    • Ice cream
    • Gelato
    Clarify This is when the egg white protein albumen is dissolved in a cold liquid and heated in order to clarify the solution. This happens because as these proteins denature through the heating process, they also attach to any other debris that may be making the liquid to be cloudy and will cause them to rise to the top of the liquid to be strained out and removed.
    • Clear soups

    Preparation:

    Eggs are one of the most versatile foods in a kitchen. It is important to note that depending on what the recipe calls for, eggs can be cooked at different times and temperatures to achieve different results. 

    Table 1.3 Coagulation Temperatures
    Type Initial Coagulation Temperature Complete Coagulation Temperature
    Egg white 140°F (60°C) 149°F–158°F (65°C–70°C)
    Egg yolk 144°F (62°C) 158°F (70°C)
    Mixed 156°F (69°C) ~

    Dry Heat:

    Frying: This can be done on a frying pan or griddle. Some form of fat is heated in the pan and the eggs is gently cracked in, carefully so as to not break the yolk. The eggs can then be cooked until the desired results are reached:

    Table 1.4 Egg Frying Methods
    Frying Method Result
    Sunny Side Up Cooked until the whites are set but the yolk is still soft and runny.
    Over Easy Cooked on one side until the whites are about 75% set and then flipped over to cook but the yolk is still soft.
    Over Medium Cooked on one side until the whites are about 75% set and then flipped over to cook but the yolk is partially set.
    Over Hard Cooked on one side until the whites are about 75% set and then flipped over to cook but the yolk fully set.

    Scrambled Eggs: The egg is beaten while still raw along with any seasonings and some form of liquid like milk or cream. This mixture is then poured into a heated skillet and the heat is reduced. Then the eggs are stirred very gently to move the cooked egg aside and make way for the remaining raw liquid until the whole mixture is cooked.

    Omelets:  Eggs are beaten and cooked, then rolled or folded over either with or without fillings.

    Baking: Eggs can be baked in many different ways. A shirred egg is an egg that is cracked into a small container and baked until fully cooked. A meringue is also a baked egg dish and is the combination of air, sugar and egg whites beaten to form a foam and the baked. Souffles are also a result of baked eggs which are a combination of egg white foam and egg yolk foam folded together with other ingredients and baked, resulting in a light and fluffy dish.

    Moist Heat:

    Hard or Soft “Boiled” : This method calls for the eggs to be submerged under simmering or boiling water (depending on the type of boiled egg desired) with the shells still on. Eggs should be simmered for hard boiled eggs to avoid the reaction of iron to ferrous sulfide and to avoid a rubber egg white. Timing is as follows: 

    • Soft: 3 to 4 minutes
    • Medium: 5 to 7 minutes
    • Hard: 12 to 15 minutes

    Coddling: This is when an egg is broken into a small dish called a coddler which is made of ceramic or heatproof glass and a screw on lid. This is then submerged in simmering water until the egg is fully cooked. Other ingredients can be added to this (bell pepper, onions, ham, etc.)

    Poaching: This is when an egg is cracked into either plain water or a mixture of water and vinegar/salt (this is done to speed up coagulation of the egg whites) and allows the eggs to "boil" without the shell. This is usually done for more runny eggs to be used on top of other foods like toast or an English muffin.

    Custards: This is a mixture of milk, cream, sugar and egg. As the mixture is cooked (can be in a water bath in the oven or over a double boiler for a loose custard) the egg coagulates and begins to set the rest of the ingredients as well.

    ***Note: DO NOT microwave whole eggs with their shell as air can expand which will lead to pressure build up and can burst the egg even after it is taken out of the microwave.

    Safety:

    The chance of an egg being contaminated internally are very low and usually the culprit if salmonella outbreaks can be traced back to improper handling and Preparation after the contents of the egg have already been separated from the shell. Regardless, individuals (especially at risk populations) should always handle eggs with care just in case there is internal contamination due to the hen carrying the bacteria and passing it along through the egg. By understanding and adhering to the following guidelines, you can minimize the chances of contracting a Foodborne illness from eggs such as salmonella:

    • Purchasing: Always purchase refrigerated eggs and double check to make sure that there are no cracks present and that the eggs are clean.
    • Cooking: Always make sure to fully cook eggs and to reduce contact with any other raw eggs after the cooking process is complete.
    • Storage: Always keep eggs and egg products refrigerated.

    Inspection and grading

    "The Egg Products Inspection Act (EPIA), passed by Congress in 1970, sets forth requirements to ensure that eggs and egg products are wholesome, otherwise not adulterated, and properly labeled and packaged to protect the health and welfare of consumers of these products." (USDA)

    Grading:

    Once eggs have passed the inspection step, they can be graded by a USDA official. The best-quality eggs are graded USDA Grade AA and the next level is USDA Grade A. USDA Grade B is the lowest grade and is only is available to food service establishments. There are three methods used to grade eggs:

    • Candling: candling when a light is shone directly into an egg in order to expose it's contents and determine it's quality. This used to be done using candles (hence the name) but is now done using a mechanically rotating surface where the eggs will be run through with a light underneath it.
    • Appearance: this is exactly what it sounds like because the egg is rated based on external shell appearance as well as internal by breaking the egg and actually looking at the albumen, yolk and other Components outside of the shell.
    • Haugh Units: This method requires an egg to be broken onto a flat surface in order to determine freshness. Eggs are randomly selected from the line using a micrometer and broken over the flat surface. The Haugh unit is then calculated by mathematically adding the thick portion of the albumen's height with the egg’s weight, and then converting the result into a Haugh unit using a formula/table. As Haugh units  and egg quality are directly correlated so as the unit decreases the quality also decreases:
      • Grade AA: Haugh unit of 72 or higher

      • Grade A: Haugh unit of 60 to 71

      • Grade B: Haugh unit of 31 to 59

    Sources:


    2.6: Eggs is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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