United States Grade Standards for Shell Eggs

A graded pack of eggs is described twice over. Quality — AA, A, or B — reflects the condition of the shell and the interior. Weight class — Jumbo, Extra Large, Large, Medium, Small, or Peewee — reflects mass, and is applied on a per-dozen basis rather than to each individual egg. Neither implies the other. A carton of Grade AA Medium and a carton of Grade A Jumbo are both entirely coherent descriptions, and the common assumption that a bigger egg is a better egg has no basis in the standard.

Quality grading looks at four things, two on the outside of the egg and two within it:

• Shell — soundness, cleanliness, shape, and texture
• Air cell — its depth, and whether it is free or fixed in place
• White (albumen) — clarity and firmness, which decline as the egg ages
• Yolk — how well defined its outline is, and freedom from defects

The grades sit on a continuum of interior condition rather than describing different kinds of egg. AA describes an egg whose white is firm and whose yolk stands high with a well-defined outline; A describes an egg that is a step along the same path; B describes one whose white has thinned and whose yolk has flattened and spread further, and which may carry shell blemishes. That continuum is chiefly a function of age and storage temperature — a Grade AA egg becomes a Grade A egg by sitting still, and no handling reverses the direction of travel.

Because interior quality declines with time, a grade is a statement about the egg at the moment it was graded. It is not a durable property of the pack, which is why the grade and the dates on a carton answer different questions and neither substitutes for the other.

The characteristic technique of egg grading is candling — passing the egg over a bright light so the interior can be judged through the shell. The name is literal in origin: the practice predates electric light and once used a candle. Modern packing lines candle at speed, and the same principle underlies automated systems that detect cracks and inclusions.

Candling reveals the air cell’s size and mobility, the shadow and movement of the yolk, the condition of the white, and internal defects such as blood spots and meat spots. What it offers is speed and the fact that the egg survives the assessment — a decisive advantage when every unit is being judged individually. What it costs is directness: candling is inference through a shell, so the standards also provide for breaking out samples to verify interior quality against the specified criteria.

The grade describes appearance and physical condition at the time of grading. It is not a food-safety determination, and it carries no information about how the hens were housed or fed — cage-free, free-range, organic, and similar claims are separate labelling schemes with their own rules and are wholly independent of the AA/A/B grade. Nor does the grade travel: an egg graded AA at the packer is not AA forever.