I started this article thinking it would be a simple table of egg grades and quality factors. But as I started researching the matter, I found that there is a lot of interesting information regarding eggs. I examine the structure of the egg, the effects of freshness, actual grading, and even dispel some common misconceptions regarding free-range and organic eggs and brown verses white eggs. So, which is a better egg, Grade A or Grade AA, brown or white, free-range, organic or neither? Let us find out.
Basic Egg Facts
Composition of the egg

Inside on an eggDiagram courtesy of Alberta Egg Producers
Air Cell
The air cell can be the first indicator of egg quality. Air cells of no greater than 1/8 inch in height are of grade AA quality. Larger air cells up to 3/16 of an inch may be classified as grade A, air cells greater than 3/16 of one inch can only be grade B.
Albume
Albume is better known as the egg white. There are two distinct albume: a thick and a thin. Albumen accounts for most of an egg’s liquid weight (about 67%). It contains more than half the egg’s total protein, niacin, riboflavin, chlorine, magnesium, potassium, sodium and sulfur. The albumen consists of 4 alternating layers of thick and thin consistencies. From the yolk outward, they are designated as the inner thick or chalaziferous white, the inner thin white, the outer thick white and the outer thin white. Egg white tends to thin out as an egg ages because its protein changes in character. That’s why fresh eggs sit up tall and firm in the pan while older ones tend to spread out.
Albumen is more opalescent than truly white. The cloudy appearance comes from carbon dioxide. As the egg ages, carbon dioxide escapes, so the albumen of older eggs is more transparent than that of fresher eggs.
When egg albumen is beaten vigorously, it foams and increases in volume 6 to 8 times. Egg foams are essential for making souffles, meringues, puffy omelets, and angel food and sponge cakes.
Chalaza
Chalaza are strands of egg white that anchor the yolk in place in the center of the albume. They are not imperfections or beginning embryos.
Germinal Disc
The germinal disc is the channel leading to the center of the yolk. The germinal disc is barely noticeable as a slight depression on the surface of the yolk.
Shell
The shell is the egg’s outer covering which is largely composed of calcium carbonate. It accounts for about 9 to 12% of its total weight depending on egg size.
Shell strength is greatly influenced by the minerals and vitamins in the hen’s diet, particularly calcium, phosphorus, manganese and Vitamin D. If the diet is deficient in calcium, for instance, the hen will produce a thin or soft-shelled egg or possibly an egg with no shell at all. Shell thickness is also related to egg size and the hen’s age. Older hens, for example, produce larger eggs with thinner shells.
Seven to 17 thousand tiny pores are distributed over the shell surface, a greater number at the large end. As the egg ages, these tiny holes permit moisture and carbon dioxide to move out and air to move in to form the air cell.
Yolk
The yolk (or yellow portion) makes up about 33% of the liquid weight of the egg. It contains all of the fat in the egg and a little less than half of the protein. A characteristic worth noting is that it is responsible for the egg’s emulsifying properties.
With the exception of riboflavin and niacin, the yolk contains a higher proportion of the egg’s vitamins than the white. All of the egg’s vitamins A, D and E are in the yolk. Egg yolks are one of the few foods naturally containing vitamin D. The yolk also contains more phosphorus, manganese, iron, iodine, copper, and calcium than the white, and it contains all of the zinc.
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