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  • The Inside of an Egg

    Written By Lisa Steele , Fresh Eggs Daily


    Eggs are nutritious and an inexpensive protein source. You probably eat them several times a week without a second thought. But did you ever wonder what exactly is inside that eggshell?

    An egg is comprised of several components including the bloom, the shell, the membrane, the white, and the yolk, but that’s just the basics - blood spots, chalazae and bulls' eyes may also be present.

    As the last step in the laying process, a thin nearly invisible layer is applied to the eggshell called the 'bloom' (sometimes also called the 'cuticle'). This covering seals the shell to help protect the egg from air and bacteria entering through the tiny pores in the eggshell and also reduces the moisture loss from the egg. Eggs should not be washed until just before using to help preserve the bloom and to help keep the egg fresh.

    Just under the eggshell is a pair of thin whitish membranes that help to keep air out of the egg.  Once an egg is laid, an air pocket begins to form between the two membranes at the blunt end of the egg. This air sac will continue to grow as the egg ages. Older hard-boiled eggs peel more easily because the air between the membranes has begun to separate the egg contents from the shell.

    The shell is the hard outer covering of the egg and is the egg's best line of defense against contamination from bacteria and germs. The shell is mostly made of calcium carbonate, with small amounts of magnesium carbonate, calcium phosphate and protein.


    The egg white, or albumen contains 60% of the protein in an egg, which is about 10% of the USRDA. Eggs are considered a complete protein because they contain all eight essential amino acids. The white of a fresh egg will be cloudy and very thick. As the egg ages, the white will become nearly transparent and thin as air flows through the pores in the eggshell.


    The egg yolk contains about 80% of the total calories and virtually all of the fat and cholesterol in the egg, along with the majority of the vitamins and minerals. The color of the yolk is determined by the level of xyanthophyll in the foods a hen eats. Xyanthophyll is a carotenoid found in marigold petals, corn, alfalfa, basil and other foods.

    The chalazae are ropy, twisted strands in the egg white that anchor the yolk in place in the center of the white. They are more prominent in fresh eggs and perfectly edible.
    Red blood (or meat) spots on an egg yolk is not an indication of fertility, but are ruptured blood vessels that have been damaged or broken during the laying process, during the travel down the oviduct, or by rough handling of the egg. As an egg ages, the yolk absorbs water from the egg white. This dilutes the blood spot, so a spot indicates that the egg is fresh.

    The blood spots are edible, but you may want to remove them before cooking the egg.  It is estimated that less than 1% of all eggs produced contain blood spots.

    If an egg has been fertilized, you will see a multi-ringed bull's eye on the yolk that indicates that the egg would likely hatch into a chick if incubated for 21 days under a hen or in an incubator. Fertilized eggs are perfectly edible and taste the same as non-fertilized eggs. The only difference is that they contain miniscule amounts of the male rooster's DNA in addition to the hen's DNA that all eggs contain.

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