Division of Animal Health and Dairy Services

• Egg Grading
• Diagnostic and Testing Services

Animal Health: Biosecurity Program

• Biosecurity for Poultry Exhibitors and Exhibitions
• Biosecurity for Poultry Facilities
• Biosecurity for Live Bird Markets
• Biosecurity for Livestock Auctions
• Biosecurity for Vehicles
• Feed and Grain Stores Selling Poultry

• Chick Brochure
• Poultryman's Handbook
• MDAR Regulation:
  330 CMR 5.00: Poulty and Eggs

Bureau of Animal Health

USDA Egg Grading Terms

Terms Descriptive of the Air Cell

Depth of Air Cell -(air space between shell membranes, normally in the large end of the egg)- The depth of the air cell is the distance from the top to its bottom when the egg is held air cell upward.

Free Air Cell - An air cell that moves freely towards the uppermost part in the egg as the egg is rotated slowly.

Bubbly Air Cell - A ruptured air cell resulting in one or more small separate air bubbles usually floating beneath the main cell.

Terms Descriptive of the Condition of the Shell

Sound - An egg whose shell is unbroken.

Check - An individual egg that has a broken shell or crack in the shell but its shell membranes are intact and its contents do not leak.

Leaker - An individual egg that has a crack or break in the shell and shell membranes to the extent that the egg contents are exuding or free to exude through the shell.

Clean - A shell that is free from foreign material and from stains or discolorations that are readily visible. An egg may be considered clean if it has only very small specks, stains, or cage marks, if such specks, stains, or cage marks are not of sufficient number or intensity to detract from the generally clean appearance of the egg. Eggs that show traces of processing oil on the shell are considered clean unless otherwise soiled.

Dirty - A shell that is unbroken and that has dirt or foreign material adhering to its surface, that has prominent stains, or that has moderate stains covering more than one-thirty-second of the shell surface if localized, or one-sixteenth of the shell surface if scattered.

Practically Normal - A shell that approximates the usual shape and is sound and free from thin spots. Ridges and rough areas that do not materially affect the shape and strength of the shell are permitted.

Abnormal - A shell that may be somewhat unusual of decidedly misshapen or faulty in soundness or strength or that may show pronounced ridges or thin spots.

Terms Descriptive of the Condition of the Yolk

Outline Slightly Defined - A yolk outline that is indistinctly indicated and appears to blend into the surrounding white as the egg is twirled.(AA Quality).

Outline Fairly Well Defined - A yolk outline that is discernible but not clearly outlined as the egg is twirled.(A Quality).

Outline Plainly Visible - A yolk outline that is clearly visible as a dark shadow when the egg is twirled.(B Quality).

Terms Descriptive of the Condition of the White

Clear - A white that is free from discolorations or from any foreign bodies floating in it. Prominent chalazas should not be confused with foreign bodies such as spots or blood clots.(AA,A,B, Quality).

Firm - A white that is sufficiently thick or viscous to prevent the yolk outline from being more than slightly defined or indistinctly indicated when the egg is twirled. (AA Quality).

Reasonably Firm - A white that is somewhat less thick or viscous than a firm white. A reasonably firm white permits the yolk to approach the shell more closely, which results in a fairly well defined yolk outline when the egg is twirled.(A Quality).

Weak and Watery - A white that is weak, thin, and generally lacking in viscosity. A weak and watery white permits the yolk to approach the shell closely, thus causing the yolk outline to appear plainly visible and dark when the egg is twirled.(B Quality).

Blood Spots or Meat Spots - Small blood spots or meat spots (aggregating not more than one-eighth inch in diameter) may be classified as B quality. If larger, or showing diffusion of blood into the white surrounding a blood spot, the egg shall be classified as loss. Blood spots shall not be due to germ development. They may be on the yolk or in the white. Meat spots may be blood spots which have lost their characteristic red color or tissue from the reproductive organs.

Bloody White - An egg which has blood diffused through the white. Such a condition may be present in new laid-eggs. Eggs with bloody whites are classed as loss.

Terms Descriptive of the Germ

Practically Free from Defects - A yolk that shows no germ development but may show other very slight defects on its surface. (AA & A Quality)

Serious Defects - A yolk that shows well developed spots or areas and other serious defects, such as olive yolks, that do not render the egg inedible.(B Quality)

Clearly Visible Germ Development - Development of the germ spot on the yolk of a fertile egg that has progressed to the point where it is plainly visible as a definite circular area or spot with no blood in evidence. (B Quality)

Inedible Eggs or Loss

Loss - An egg that is inedible, leaker, cooked, frozen, contaminated, or containing bloody whites, large blood spots, large unsightly meat spots, or foreign material.

Inedible Eggs - Inedible eggs are described in the U.S. standards to include black rots, white rots, sour eggs, eggs with green whites, musty eggs, and moldy eggs. These types of inedible eggs are usually caused by the growth of bacteria or mold on or in the egg. Other types of inedible eggs are those showing blood rings, and those containing embryo chicks (at or beyond the blood ring stage) which result from germ development in fertile eggs. Two additional types of inedible eggs are mixed rots and eggs with stuck yolks.

Inedible Eggs That May Be Detected by Candling

Stuck Yolk - Occurs when the yolk membrane becomes attached to the shell membrane. It generally occurs in older eggs that have been left in a fixed position for a long time. When the thick white becomes thin, the yolk floats close to the shell and becomes attached to the shell membrane.

Blood Due to Germ Development - Blood caused by development of the germ in a fertile egg to a point where it is visible as definite lines or as a blood ring. Such an egg is classified as inedible.

Black rots - Eggs that are generally opaque(with the exception of the air cell) when viewed before the candling light. When broken the contents have a muddy brown appearance and give off a repulsive, putrid odor. The bacteria most frequently causing this type of loss belong to a group named Proteus. However, when any rot is at an advanced stage, it may appear “black” before the candling light.

Mixed Rot - (addled eggs)Occurs when the vitelline membrane of the yolk breaks and the yolk mixes with the white. Resulting in a murkiness throughout the interior of the egg when viewed before the candling light.

Blood Rings and Embryo Chicks - These are caused by germ development, occurring in fertile eggs held at incubation temperatures. At a rather early stage in incubation(after 24 hours) the embryo develops a circulatory system. If at this stage the embryo dies the blood drains to the outer edge of the germ disc, causing the blood ring. Before the candling light, it appears as a brilliant blood-red circle from one-eighth to three-eighths of an inch in diameter, depending on the stage of development.

Inedible Eggs Which Cannot be Detected by Candling

Green Whites - Eggs with green whites can be detected by experienced graders using the standard candling light. This type of loss is caused by the Pseudomonas group of bacteria. Like sour eggs, eggs wtih green whites will fluoresce under the ultraviolet light when broken out. Eggs with green whites may or may not have a sour odor.

Moldy Eggs - Eggs that may be detected by observing mold spots on the shell or by mold growth in checked areas of the shell, or by mold growths(the odor of mold or must may or may not be present) inside the egg itself when viewed before the candling light. The use of dirty water for washing eggs and dirty processing oil cooler than the egg, and the storage of the egg in unusually high humidity encourage mold growth and mold penetration through the shell. Advanced stages of mold growth throughout the entire egg might have an appearance similar to that of black rot.

Musty Eggs - These types of eggs frequently appear clear and free from foreign material when viewed before the candling light and can genrally be detected only by the characteristic musty odor emanating from the egg. Sources of contamination may be a musty odor in the case or the nesting material, or the presence of this odor on the shell itself.

Sour Egg - Often difficult to detect by standard candling methods. Generally, eggs in this condition show a weak white and murky shadow around an off-center swollen yolk.The bacteria, causing sour eggs, belongs to a group named Pseudomonas. These organisms produce a material which fluoresces under ultraviolet light, giving off a green sheen. The adoption of ultraviolet light in candling(black light)has made the detection of this type of loss easier.

Cooked Eggs - Eggs which have been subjected to heat resulting in coagulation of the contents. Cooked eggs, when held before the candling light may be identified by the presence of threadlike shadows in the white indicating a slightly cooked egg, or a dark, opaque appearance indicating complete coagulation of the contents.

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