How can you tell the difference between a good egg and a bad egg? Eggs are rated and graded into three classifications determined by the United States Department of Agriculture (USDA). If you have chickens and plan on selling eggs, grading and sizing is required. As a general rule, you should grade all your eggs before you store, sell or consume them.
When grading eggs, both the interior and exterior quality is measured. This process does not take into account weight or shell color. According to USDA guidelines, eggs are graded and labeled as AA, A, and B. U.S. Grade AA eggs are nearly perfect. The whites are thick and firm and the yolks are free from any defects. The shells are clean and without cracks. U.S. Grade A eggs appear to be the same as Grade AA, but the difference is a slightly lower interior quality. U.S. Grade B eggs are noticeably different. They may have slight stains and be irregular in shape and size. The quality of the interior is further reduced. Grade B eggs are not sold in supermarkets, but are used commercially in powdered egg products or liquid eggs.
Begin the egg grading process by checking the quality of the shell. The ideal eggshell is clean, smooth and oval in shape with one end slightly bigger than the other. Eggs with cracked or broken shells should be discarded. If you are selling the eggs, remove any with unusual shapes, textures or thin spots on the shell. While they are edible, they break easily and will be unacceptable because of their appearance.
Grading the interior of the egg is performed by a method called candling. Using an egg candler will allow you to examine the air cell, the egg white (called albumen) and the yolk. Candling also lets you check for spots and cracks. Listed below are the different components to observe when candling an egg:
Air Cell Depth - The air cell is the empty space between the shell and the white usually found at the bigger end of the egg. As the egg ages, the air cell depth grows and the quality of the egg diminishes.
White or Albumen - The white of the egg is called the albumen. The quality is based on its clarity and thickness. Look for a clear color without discolorations or floating foreign matter. Thick albumen allows limited movement of the yolk and indicates a higher quality egg.
Yolk - The quality of the yolk is determined by the distinctness of its outline and other features like size, shape and absence of any blemishes or blood spots. It should be surrounded by a dense layer of albumen.
Spots - Candling can help reveal foreign matter like blood spots or meat spots. Eggs with interior spots should not be sold.
USDA Grade Standard Chart: This table is a quick reference for determining the grade of an egg by candling. (From the article: Proper Handling of Eggs: From Hen to Consumption by the Virginia Cooperative Extension)
If you plan on selling your eggs, you need to sort and size them. Large and extra large eggs are the best sellers. You might be surprised to learn that eggs are not sized individually, but rather sized by the combined weight of one dozen eggs. A size breakdown by weight can be found in the chart on the right.
While there are a few things to learn about grading and sizing eggs, the process is not difficult. You will be able to master the technique quickly with just a little bit of practice.
For more information about grading and sizing eggs, you can refer to the Virginia Cooperative Extension and the American Egg Board.