As a follow-up to our egg formation post last week, now that we have a better understanding of what it takes to produce even one fresh egg, we thought we’d look a little closer at standard US egg grading, sizing, and freshness.

Egg Grading

Do you know what a USDA Grade AA egg is, versus a Grade A egg?  Have you ever seen a Grade B egg?  Most eggs sold commercially are graded, sorted, and packaged at US Department of Agriculture regulated facilities. Grades are assigned to eggs based on the interior quality of the egg, and the appearance and overall condition of the egg shell. Egg size has no relationship to egg grade.

Commercially packed eggs show the egg grade, and egg size on the carton

According to USDA guidelines, eggs are graded, in descending order as:

U.S. Grade AA – eggs have whites that are thick and firm; yolks that are high, round, and practically free from defects (including blood spots, and meat spots); and clean, unbroken shells.  Air cell depth may not exceed 3.2mm.

U.S. Grade A – eggs have characteristics of Grade AA eggs except the whites are “reasonably” firm. This is the quality most often sold in stores.

U.S. Grade B – eggs have whites that may be thinner and yolks that may be wider and flatter than eggs of higher grades. The shells must be unbroken, but may show slight stains. This quality is seldom found in retail stores because they are usually used to make liquid, frozen, and dried egg products, as well as other egg-containing products.


This egg, although perfectly safe to eat, fails US AA and A grading because of the large blood spot

If you want fresh grade AA eggs, you really need to raise your own hens. Note that ‘grade’ is assigned to the eggs only, grade of the egg states nothing about the conditions under which the hens are raised.

Egg Sizing

Most consumers don’t think about egg-sizing.  A recipe calls for one or two large eggs, most of us simply open the refrigerator, open an egg box, and retrieve the egg we need without a second thought.

You might assume that if you purchase a carton of “Large” Grade A eggs from the supermarket, that all of the eggs in the box fall into some definition of “Large”, but you’d be wrong.  Eggs aren’t packaged by individual egg weight.  Eggs packaged in containers marked “Medium”, “Large”, “Extra-Large” or “Jumbo”, simply are packaged by total carton weight, per one dozen eggs.  Referring to the chart below, the first column is the ‘size’, and the next column lists, in ounces, the total weight of one dozen eggs (a carton) for that egg size, as defined by the USDA.

In the United States, egg sizes are based on total carton weight per dozen

This means that one dozen “Large” eggs could contain some eggs that are significantly smaller, or larger than others, providing the total carton weight is approximately 24 ounces, all eggs in that carton are, based on an average, “Large” for the purpose of sale. This means a large egg should weigh, on average,  2 ounces.  That’s all it is, an average weight.

If you raise your own chickens, your eggs don’t come pre-graded or sorted by size.

You may raise bantam chickens, that lay smaller eggs than standard breeds, or like us, you may have young pullets that start out laying peewee eggs, or old hens that routinely lay jumbo eggs.  If you simply cook your eggs in an omelet, scrambled, boiled, or fried, sizing isn’t really that important.  However, if you’re baking with eggs, especially more sensitive recipes like souffles, crème brûlée and custards, the size of the eggs becomes much more important.

Depending on age and breed, our eggs show some significant differences in size

Our smallest pullet eggs a few weeks ago were peewee-sized (based on USDA average per egg weights) at 34 grams in weight.  Our pullets have been laying now for just over 30 days, and their average egg weight now is closer 50 grams, or medium-sized.  However, our mature hens only lay jumbo eggs, between 68-72 grams.

To show the difference egg size can make in some recipes, this frittata typically uses 2 cups (16 fl oz) by volume of fresh eggs.

This tomato, basil, and fresh mozzarella frittata usually uses 8 hens eggs

In the past, for our young standard breed hens, on average that has been equal to approximately 8 eggs for 16 fl oz.  However, when I made this frittata last week with our young pullet eggs, it took 12 whole eggs to equal 16 fl oz.  That’s four more eggs than we typically use.

If you raise chickens it's helpful to have an egg scale in the kitchen

This is a recipe I make often, so I happened to know by volume how much egg we usually use and the conversion was simple, but most recipes don’t list egg usage by volume, they only state size, so it’s helpful to have a rough idea as to the size of the eggs your hens are laying, and an egg-scale becomes a valuable kitchen tool to have around.

Egg Freshness

We know our eggs are fresh, as every morning we pull them, still warm from the nest boxes (lately, usually from underneath one of two broody Buff Orpingtons).

We know these eggs are fresh!

If you purchase your eggs from the Farmer’s Market, they likely were laid sometime that week, and if there’s any doubt, you can ask the vendor.  However, if you buy your eggs at the supermarket, how fresh are they, really?  They’re laid, graded, sorted, washed, packaged, loaded on trucks, transported, and eventually stacked on the shelves of market refrigerators, and can remain there up to their “sell-by” date.  You can ask the store manager how fresh the eggs are, but he or she likely won’t be able to tell you, unless they can read the code stamped on the end of an egg carton.

So, how do you read egg carton codes?

This egg carton shows the date the eggs were packaged, the sell-by date, and the facility code where the eggs were packed

This carton code begins with a three digit code, the Julian Date, that is the day the eggs were packaged into the carton (NOT when they were laid).  This three digit number represents the day of the year.  As there are 365 days in a year, day 238 would be August 26th.  You can use simple online Julian-to-Calendar-Date converters online to help calculate this value for you.

The most familiar part of the code listed is the “sell-by” date, in this case “Sept25”.  Here we can see that these eggs should be sold by September 25.  When a “sell-by” date appears on a carton bearing the USDA grade shield, the code date may not exceed 45 days from the date of packing.  This means that if you’re eating eggs close to the sell-by date, they could already be at least five weeks old.

The code below the date information, is the packaging plant code, where the eggs were graded, sorted, and packed.

Eggs from your own chickens however don’t come pre-stamped with a sell-by date.  An easy test to determine if your eggs are fresh, or old, is to float them in water.  As eggs age, the air cell enlarges, so older eggs are more buoyant when floated in a bowl of water than fresh eggs, which will sink.  An egg that floats isn’t necessarily bad, but it is old.

This very fresh egg, laid this morning, sinks to the bottom of the bowl when floated in water

There are clues as to how fresh your eggs are when they’re cracked open into a bowl too.  A cloudy white (albumen) is a sign the egg is very fresh.  Even we were surprised the first time we noticed this.  Market egg whites are rarely cloudy.  A clear egg white is an indication the egg is aging.   As eggs age, the egg white also becomes thinner, and the chalaza become weaker and less prominent, causing the yolk position to move off center.  Foul odors obviously indicate the egg has spoiled, and should be discarded.

There’s nothing better than a truly fresh egg.  How old are the eggs in your refrigerator?