What are the true, legal definitions of the various grades and sizes of eggs that you see in the grocery store? Here are their definitions!
The grade of a shell egg is determined by the size of the internal air-cell. As an egg ages, the liquid contents evaporate through its pores. The larger the air-cell is, the lower the grade of the egg. The outside appearance also factors into the grade of an egg. Eggs with moderate staining (but not adhering dirt) can be sold as grade "B." All other grades require a clean, unblemished shell appearance. Dirty eggs cannot be sold to consumers. The size of an egg is determined by its weight, in grams. A small egg must weight 40.16 grams or more, a jumbo egg must weigh 68.51 grams or more.
The nutritional value and taste of all the grades is the same.
Eggs also are sold in a bewildering variety of sizes, which are based on their weight, not volume. The size markings on egg cartons tell the minimum net weight for a dozen eggs. The size names and weight per egg is given below:
|Size or Weight Class||
|Size or Weight Class||
|Jumbo||2.42 ounces||Medium||1.67 ounces|
|Extra Large||2.17 ounces||Small||1.42 ounces|
|Large||1.92 ounces||Peewee||no min|
NOTE: If you are unsure of the size of your eggs, label them the smallest size. For example, if you have at least medium sized eggs, label the carton as Medium. It is acceptable to have larger sized eggs in the carton.
(see USDA Shell Egg Grades & Standards)
Whte, brown or other color, the color of an egg's shell does not affect its nutritional value, they're all the same. It's just a pigment in the shell, genetically determined. Leghorns lay white eggs. Ameraucanas lay blue eggs. Olive eggers lay olive green eggs. And Orpingtons lay brown eggs.
Egg processors typically print dates commonly called "Code Dates" on cartons. sometimes they say "EXP," "Sell By," and "Best if Used Before". The use of code dates on USDA graded eggs is optional; it is NOT required by federal law. But, if they are used, certain rules must be followed:
Another type of code dating used indicates the recommended maximum length of time that the consumer can expect eggs to maintain their quality when stored under ideal conditions. Terminology such as "Use by", "Use before", "Best before" indicates a period that the eggs should be consumed before overall quality diminishes. Code dating using these terms may not exceed 45 days including the day the eggs were packed into the carton.
There is much more to eggs that just the size and grade!
Candling is the process of using light to help determine the quality of an egg. A small producer may still inspect by holding them up to a candle. 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. Large scale farms use automated mass-scanning equipment to detect eggs with cracked shells and interior defects. During candling, eggs travel along a conveyor belt and pass over mechanical sensors integrated with computerized systems for segregation of defective eggs. Manual scanning techniques involve conveying the eggs over a light source where the defects become visible and the defective eggs are segregated. Hand candling-holding a shell egg directly in front of a light source—is done to spot check and determine accuracy in grading. Advanced technology, utilizing computerized integrated cameras and sound wave technology, is also being applied for the segregation of eggs.
If you've ever peeled a hard boiled egg, you've seen the air space at the wider end of the egg. That's an air cell.
Eggs take in air as they age, but the the size of the air cell varies even at the moment they are laid, so it does not necessarily relate to freshness.
An egg industry website has more detailed information on the follow topics: