GRADING Classification determined by interior and exterior quality and designated by letters-AA, A and B. In many egg packing plants, the USDA provides a grading service for shell eggs. Its official grade shield certifies that the eggs have been graded under federal supervision according to USDA standards and regulations. The grading service is not mandatory. Other eggs are packed under state regulations which must meet or exceed federal standards.
In the grading process, eggs are examined for both interior and exterior quality and are sorted according to weight (size). Grade quality and size are not related to one another. In descending order of quality grades are AA, A and B.
EXTERIOR The first step in egg grading is inspection of the shell for cleanliness, soundness, apparent texture, strength and shape. Shell color is not a factor in judging quality.
To pass grading requirements, all eggs must be clean, but a certain amount of staining is permitted in the lower grade. All eggs must have sound shells. Those with cracks or markedly unsound shells are classified as restricted eggs.
The ideal shell shape is oval with one end larger than the other. Abnormal shells, permitted under B quality, may be decidedly misshapen or faulty in texture with ridges, thin spots or rough areas.
INTERIOR Inspection of the interior is the next step in grading. This is accomplished by candling or by the breakout method using the Haugh Unit system to evaluate the air cell, the albumen and the yolk.
Higher grade eggs have a very shallow air cell. In AA quality eggs, the air cell may not exceed 1/8 inch in depth. Eggs of A quality may have air cells over 3/16 inch in depth There is no limit on air cell size in Grade B.
Albumen is judged on the basis of clarity and firmness or thickness. A clear albumen is defined as being free from discolorations or from any floating foreign bodies.
Factors determining yolk quality are distinctness of outline, size and shape and absence of such defects as blemishes or mottling, germ development or blood spots.
When eggs are twirled before the candling light, the yolk swings toward the shell. The distinctness of the yolk outline depends on how close to the shell the yolk moves, which is, in turn, influenced by the thickness of the surrounding albumen. Thick albumen permits limited yolk movement while thin albumen permits greater movement. -see Buying, Egg Products Inspection Act, Formation, Shell