Classification determined by the interior and exterior quality of the egg at the time it is packed. In some egg-packing plants, the U.S. Department of Agriculture (USDA) provides a voluntary grading service for shell eggs. The official USDA grade shield on an egg carton certifies that the eggs have been processed, packaged and certified under federal supervision according to the U.S. Standards, Grades and Weight Classes for Shell Eggs established by USDA. Plant processing equipment, facilities, sanitation and operating procedures are continuously monitored by the USDA egg grader.
In the grading process, eggs are examined for both interior and exterior quality before they’re sorted according to weight (size). Grade quality and weight (size) are not related to one another. Eggs of any quality grade may differ in weight (size). In descending order of quality, grades are designated AA, A and B.
The first step in egg grading is to examine the shell for cleanliness, soundness, texture and shape. Shell color isn’t a factor in judging quality. All eggs must be clean to pass grading requirements, but a small amount of staining is permitted in Grade B. All eggs must have unbroken shells. Eggshells with cracks or markedly unsound, or flawed, shells are classified as restricted eggs. The ideal eggshell shape is oval with one end larger than the other. Abnormal shells, permitted for Grade B eggs, may be decidedly misshapen or faulty in texture with ridges, thin spots or rough areas.
The next step in grading is examination of the interior of the egg. This is done by candling or by the breakout method using the Haugh unit system to evaluate the albumen (white), yolk and air cell (not done in commercial processing). Albumen is judged on the basis of clarity and firmness or thickness. A clear albumen is free from discolorations or from any floating foreign bodies. When an egg is rotated over the candling light, its yolk swings toward the shell. The distinctness of the yolk outline depends on how close to the shell the yolk moves, which is influenced by the thickness of the surrounding albumen. Thick albumen permits limited yolk movement while thin albumen permits greater movement – the less movement, the thicker the white and the higher the grade. Factors determining yolk quality are distinctness of outline, size and shape and absence of such defects as blemishes or mottling, embryo development or blood spots. Higher-grade eggs have shallower air cells. In Grade AA eggs, the air cell may not exceed 1/8 inch in depth and is about the size of a dime. Grade A eggs may have air cells over 3/16 inch in depth. There is no limit on air cell size for Grade-B eggs. While air-cell size is considered in grading and eggs take in air as they age, the size of the air cell does not necessarily relate to freshness because size varies from the moment contraction occurs after laying. To judge freshness, use carton dates.
– See Air Cell, Blood Spots, Breakout, Buying, Candling, Egg Products Inspection Act, Formation, Haugh Unit, Restricted Eggs, Shell, Yolk