Everything You Need to Know About the Egg Grading System
Posted on: July 18th 2022
When you’re browsing the egg section at your local grocery store, you’re probably just thinking about grabbing the best-looking carton you can find within your price range and getting out of there. You’re used to seeing cartons containing eggs of similar colors and sizes, with a United States Department of Agriculture (USDA) seal but how do they get that way? At some point, you may have wondered what exactly the little shield reading USDA means, how your eggs were sorted and what their grade means.
The USDA has grouped the eggs you see in the store using their grading system. You might be surprised to find out that it’s not actually required for producers to have their eggs graded at all. In many cases, backyard egg producers and small farms opt to sell directly to consumers without the USDA performing grading, which means it’s up to individual states to set their own regulations.
In North Carolina, for example, there is a law specifically for small flock egg producers to follow if they want to sell their ungraded eggs. The main restriction is that these producers can only sell 30 dozen or fewer ungraded eggs per week. In Oregon, farm-to-table culture has consumers buying lots of fresh, ungraded eggs from local farmers or neighbors regularly. Their state law was recently changed to remove the grading requirement for producers who sell eggs directly to consumers.
Why the USDA Grades Eggs
When you’re buying farmer’s market or backyard eggs, you’re probably doing so because you know they’re of good quality. You probably don’t mind a little variation in size or shell color, for example. But when eggs are produced in large quantities from a larger number of chickens, the range of quality possibilities expands dramatically. The USDA’s egg grading service continuously monitors quality and size during the packing process, to make sure eggs meet a certain standard.
Grades allow consumers to look at a carton of eggs and know roughly the type of quality they will get. The grading process takes into account several characteristics:
- Shell appearance
- Shell condition
- Yolk quality
- White quality
What are the egg grades an inspector can decide on? The possible quality ratings for eggs are AA, A or B. An egg can only be graded based on the factor that earns the lowest rating, so even if the yolk and white quality are AA-worthy, the egg will still be graded a B if its exterior has certain flaws that earn it a B grade.
When eggs are entered into the grading program, the USDA also checks processing equipment and facilities as well as sanitation and operating procedures. As long as these elements meet program standards, the processed eggs can display the USDA grademark shield.
Exterior Grading Factors
How are eggs graded? And what’s the difference between Grade A and AA eggs? It starts with the outside appearance. It’s pretty easy to describe an egg, and when you do, you’re likely describing a top-of-the-line Grade AA product. The immediate image that typically springs to mind is a smooth, white, oblong object, but not every egg meets that description. Let’s dig deeper into the factors that USDA graders take into account when assigning exterior egg grades.
1. Shell Color
Although there is a pervasive myth that brown eggs are better for you, this is not the case. Eggs get their shell color from the laying hen’s genetics. If the hen has white feathers, she’ll likely lay white eggs, and if she has brown feathers, she’s likely to lay brown eggs. There’s no difference in nutrition that can be tied directly to egg color. The reason eggs are sorted by color in cartons is simply that they sell better that way. While a producer may opt not to include eggs that are off-color in some way, USDA graders do not take shell color into account.
The only notable difference between white and brown eggs is that brown eggs are more difficult to grade on interior quality because the shells are harder to see through. Certain imperfections and quality indicators like small blood spots or meat spots are more prevalent in brown eggs, according to the USDA Egg Grading Manual.
2. Shell Shape and Texture
The first thing USDA graders look for is shell quality and the overall shape of the egg. Normally, eggs are an oval shape in which one end is larger and rounder, and the smaller end tapers. There’s no fancy terminology here — the ends are referred to as the large end and the small end. If you want to be more formal, the large end is sometimes referred to as the air cell end.
When graders are investigating, they use a photo of the ideal egg shape to compare it to the eggs they are grading. An egg can have some considerable variation from the ideal and still be graded an AA or A. As long as the egg fits the large-end-small-end shape, it can have slight ridges or rough areas. If the shell is unusually shaped, has pronounced ridges, or has thin spots, the grade is lowered to B quality.
3. Shell Soundness
The strength of an egg’s shell is crucial to successful transport and storage, so graders check this as well. There are three soundness ratings an egg can possess:
- Sound: The shell is completely unbroken.
- Check: The egg has a break or crack in the shell, but the interior membranes are intact.
- Leaker: The egg is cracked or broken, and the contents of the egg can leak or are leaking out.
Needless to say, leakers are taken off the line immediately to make sure that they don’t become damaged further. It’s also essential that they don’t leak any liquid on other eggs, packaging material, or inspection equipment. While leakers are a definite loss, check eggs can be used for other purposes because their interior contents remain intact.
Sometimes egg shells crack while still inside the hen’s body. When that happens, the shell can be repaired by extra deposits of shell around the cracked region, which leads to a ridged area. This doesn’t compromise the shell’s soundness, but depending on the degree of ridging, may affect the grade given for shape and texture.
4. Shell Cleanliness
When eggs are processed by machine, the cleanliness inspection usually follows the washing process. It’s essential for the inspection to take place in a well-lit area with enough space for the grader to remove any eggs that don’t make the cleanliness cut. There are only two descriptions for determining the cleanliness of an individual egg.
A clean egg’s shell has no foreign materials, stains, or discolorations visible to the naked eye. If an egg has a few small specks, marks from the cage, or very small stains, it can still earn the “clean” designation as long as the marks aren’t too numerous or obvious to detract from the egg’s clean appearance. Processing oil traces can also be deemed acceptable.
A dirty egg has dirt or some type of other foreign material stuck to the shell. It may also have moderate or prominent stains. If the marks are all clustered together in one spot and cover more than one-thirty-second of the shell’s surface, the egg is dirty. If the marks are scattered across the shell, the egg is dirty when the coverage exceeds one-sixteenth of the shell.
Cleanliness is a bit of a judgment call for the graders, as it’s pretty tough to gauge exactly what one-sixteenth or one-thirty-second of an egg is. When the markings are partially clustered and partially scattered, things get even more complicated. Due to the slightly subjective nature of this process, graders usually err on the safe side and mark an egg dirty if there’s some question as to its cleanliness. Dirty eggs don’t get a grade at all.
Interior Grading Factors
Shells are important for visual appeal, but their primary purpose is to protect the delicious and nutritious contents of the egg. The majority of a grader’s job is to evaluate the interior of the egg through candling. Originally, the process of candling involved holding a candle flame under an egg and using the light to see whether an embryo was growing inside the egg.
We’ve now realized that candling can be used to inspect the quality of an egg’s contents and upgraded to LED lights, but the idea behind it is the same. To make sure their candling yields accurate grading information, graders will also crack a few eggs for confirmation. When candling and breaking eggs for interior quality, graders check the following factors.
1. Depth of Air Cell
You may have noticed that when you boil an egg and peel it, one end is flat because the egg doesn’t occupy the whole shell. That space, usually at the large end of the egg, is called the air cell. A freshly-laid egg has barely any air cell at all. As the temperature of the egg decreases, the liquids within contract. As time goes on, water may evaporate from the egg and increase the size of the air cell.
Graders check the air cell visually to make sure it’s under these specifications:
- Grade AA: 1/8 inch
- Grade A: 3/16 inch
- Grade B: No limit
The air cell measurement has less of an impact on the end grade than the other interior grading factors.
2. Yolk Quality
You already know the quality of the yolk is central to the overall quality of the egg, and the grading system reflects this. There are many factors inspected during grading, most of which can be grouped into tests of the shape, color, and condition of the yolk.
To check the yolk’s condition, graders look for the absence or presence of dark shadows or blemishes. As you can imagine, checking the color of the yolk is much easier to do by breaking the egg. However, an off-color yolk can produce a gray or green-tinted shadow during candling. The outline of the yolk matters too. Grade AA eggs have an indistinct outline that fades into the white. Grade A eggs have a discernible but unclear outline. If the egg yolk outline is visible and has a dark shadow, it’s a grade B.
In terms of size and shape, the freshest eggs are round and pleasantly firm. The membrane of the yolk weakens over time and lets water in. This increases the size and weight of the yolk. The size and shape of the yolk are only notable when they are considerably distorted and noticeable, in which case the egg is graded a B.
3. White Quality
Also known as the albumen, the egg white is a crucial factor in the grade an egg receives. The two elements in judging white quality are clarity and firmness. Firmness is judged by a measurement called the Haugh unit. The Haugh unit correlates the egg weight with the height of the white. These are the three levels of albumen quality:
- Firm: The white is thick enough that the outline of the yolk is barely distinct when the egg is candled. A firm albumen’s Haugh unit measures 72 or more and earns an egg AA quality.
- Reasonably firm: In a reasonably firm egg, the white is thin enough to let the yolk closer to the shell, and the result is a more defined yolk observed during candling. An egg with a reasonably firm white will have a Haugh value between 60 and 71 and can receive an A grade.
- Weak and watery: If the egg white has low viscosity and a Haugh unit below 60, it can receive no higher than a B grade.
In terms of clarity, grade AA and A eggs must be free of any blood or meat spots in the white. If small spots are present and don’t spread into the albumen around them, the egg can be classified a B.
4. Disqualifying Factors
Many qualities cause eggs to be counted as a loss. Not all of them indicate that an egg is inedible, but they all result in eggs failing to achieve the USDA grades necessary for selling them.
- Bloody white: If an egg has blood spread throughout the albumen, it’s considered a loss.
- Cooked eggs: These eggs have suffered the effects of heat at some point during processing, and candling them shows coagulation or “cooking” of their interiors.
- Musty eggs: Not everything can be determined visually. Musty eggs have been contaminated by bacteria and give off an unpleasant odor even though they look normal when candled.
- Moldy eggs: Whether it’s present on the outside or visible through candling, mold is something that always results in a loss egg.
- Green whites: It’s harder to catch, but experienced graders sometimes encounter green whites. This condition is caused by a group of bacteria that make the whites fluoresce under ultraviolet light.
- Black, white or mixed rot: This is exactly what it sounds like, and can be detected through abnormalities in the candling inspection.
You definitely don’t want to discover any of these types of eggs in your carton. They unpleasantly smelly when you crack them open, and they can be dangerous to your health. One of the greatest advantages to USDA grading is the elimination of these eggs before they can ever reach your kitchen counters.
Even with all the intense scrutiny the USDA puts into egg grading, eggs are a natural product with natural differences. So how do they ensure that all graded eggs end up packaged with others of the same quality? They allow for some slight variation within cartons of each grade. Here’s the breakdown of what a carton of each grade must contain:
- Grade AA: Must contain at least 72 percent AA quality eggs. The remainder must be at least 10 percent A quality, and the rest can be B quality. Not more than 7 percent of check eggs are permitted.
- Grade A: Must contain at least 82 percent A quality or better eggs. The rest can be up to 18 percent B quality with 7 percent checks.
- Grade B: Must contain at least 90 percent B quality eggs, with no more than 10 percent checks.
The slight overlap of the grades allows for some wiggle room for producers while upholding the rigorous USDA quality standards that govern each grade.
The sizing of eggs is completely independent of their grade. You may be surprised to learn that the size on the carton does not apply to each individual egg, but rather refers to a minimum weight per dozen. Eggs are weighed by an electronic scale and then sorted by these minimums:
- Peewee: 15 ounces per dozen
- Small: 18 ounces per dozen
- Medium: 21 ounces per dozen
- Large: 24 ounces per dozen
- Extra Large: 27 ounces per dozen
- Jumbo: 30 ounces per dozen
It’s quite rare to find small eggs in a grocery store, and you may not have even heard of peewee eggs before. Most recipes call for large eggs, although extra large usually doesn’t make a noticeable difference.
What Does the Grade of an Egg Mean for Cooking?
Now that you understand all the considerations that go into USDA egg grades, here comes the all-important question — which is the best for cooking? Naturally, AA eggs are the highest quality and will make the best choice in most applications, but here are some of the specific ways egg grade affects cooking.
- Frying and poaching: Grade AA and A eggs have firmer whites, which means they spread out less when you break them. Using grade AA eggs results in smaller, more circular fried eggs as well as tighter poaches with fewer loose strands breaking off.
- Boiling: A grade eggs actually work better for hard-cooking. Since grade AA has the smallest air cells, the membranes are tighter, and the resulting eggs are harder to peel. B grade eggs aren’t the best as the yolks are more likely to be off-center.
- Scrambling and baking: When you’re just going to mix up the eggs anyway, grade doesn’t matter. The nutrition is the same, so there’s no real downside to using grade B eggs.
Where to Find the Grade of Your Eggs
If your eggs have been graded by the USDA, you’ll find the seal on the top or side of the carton. When printed in color, look out for the blue top, white middle and red bottom on the shield. You may be surprised just how many egg producers don’t have a USDA grade. Cartons can state that they are AA, A or B grade without actually having been graded by the USDA. Because USDA grading is voluntary and can be costly, large volume producers often follow the same grading guide but don’t have their product officially tested.
Finding the Best Quality Eggs Available
The USDA grading system is a way for producers and consumers like you to communicate on the quality of eggs. This common language helps you understand what you’re paying for and ensures consistency in production. The shield grade isn’t all that goes into egg quality, however. The way animals are treated and cared for matters, too.
If you’re interested in learning more about what makes a nutritious, quality egg, start with Sauder’s. We have quality down to a science, producing 1.5 billion eggs every year with rigorous standards and passion for what we do. We invite you to explore some of the ways we ensure egg quality and experience the Sauder difference with any of our fine products.