The three USDA grades for acceptable shell eggs are U.S. Grades AA, A, and B. Canada has two acceptable grades: A and B. Quality grades do not reflect product safety or nutritional quality, and Grade B eggs - stored properly - are safe to eat and will have the same nutritional quality as higher-grade eggs.
Usually, USDA-graded eggs are washed, packed, and graded within a day to a week of being laid, but they can be legally graded for up to 30 days. They must be labeled with the date that they were packed and graded; often they will also have a sell-by or expiration date. The sell-by date is defined as no more than 30 days from the time the eggs were packed and graded. This means that USDA-graded eggs can theoretically be sold for up to two months after they are laid, although most will be sold within 30 days or less.*
Egg Grades: (a) Grade AA (b) Grade A (c) Grade B
Courtesy of U.S. Department of Agrigulture
In the grading process, eggs are examined for both interior and exterior quality before they’re sorted according to weight (size). Grade quality and size are not related to one another. 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 sound, unbroken shells. Eggshells with cracks or markedly unsound 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, yolk and air cell.
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, germ 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.**
Tomorrow I will help you size up your eggs.
* Figoni, P. (2009). How Baking Works: Exploring the Fundamentals of Baking Science. Hoboken, New Jersey. John Wiley and Sons.
**Retrieved from: http://www.incredibleegg.org/egg-facts/eggcyclopedia/g/grading