A brown egg

© iStockphoto.com/Paul Reid

chicken eggs

See also Haugh unit

In the United States, traffic in eggs is regulated under the federal Egg Products Inspection Act (1970). Both grades and sizes are defined, and the two are not related. Peewee eggs can be Grade AA and Jumbos can be Grade B.

Grades

A “grade shield” on the packaging indicates the eggs have been graded under federal supervision, as most have. Some states do their own grading; they can display a grade but not the USDA grade shield. In order of decreasing quality, grades are AA, A, and B. All ungraded eggs sold to consumers must meet B standards. “Restricted eggs” do not meet B standards; their disposition is regulated to prevent them from reaching consumers, although two types of restricted eggs, checks (the shell is cracked but the membrane beneath is not broken), and dirties, may be sold to factories equipped to process them properly.

All graded eggs must be clean and have sound, whole shells. Grade B may show some staining, provided it covers less than 25% of the shell, and the shell may be misshapen or have thin spots, ridges, and other textural defects. There are no color requirements.

The main difference between the grades is internal, and mostly reflects the freshness of the egg. The air cell in a grade AA egg must not be more than 1/8 inch deep; in a grade B egg it is over 3/16 inch deep. The egg white should be thick and clear; the yolk firm and well-defined.

Candling–placing a very strong light behind the egg can reveal more about the egg than one might think. For example, if the egg white is thin, twirling the egg will make the yolk move nearer to the shell than it would if the egg white were thicker.

drawing showing appearance of broken eggs of different qualities: the lower the quality, the more the white and yolk spread out

Quality is more obvious once the egg is broken. The yolk of a grade AA egg is tall; the white doesn't spread out much, and there is more thick white than thin white. The yolk of a grade B egg is flattened, it has more thin white than thick white and will spread out to cover a larger area. The USDA has developed a test of egg quality based, for example, on measurements of the height of the egg white on a flat plate; the results are stated in Haugh units.

Sizes

U.S. sizes are defined by the weight of a dozen eggs. (Not individual eggs.  An egg in a carton of Extra Large eggs need not weigh at least 27/12 ounces, but the dozen must weigh at least 27 ounces.)

Size Weight of a dozen eggs
Jumbo 30 ounces
Extra Large 27 ounces
Large 24 ounces
Medium 21 ounces
Small 18 ounces
Peewee 15 ounces

Most recipes that call for eggs usually mean Large eggs. Below is a chart that may be used to convert a number of Large eggs to an approximate equivalent in other sizes.

About 11% of a chicken egg's weight is shell.

Regulations Governing the Grading of Shell Egg and Egg Products, USDA 7 CFR, Part 59, GPO May 1, 1991.

How Long Do Eggs Keep?

According to the U.S.D.A, store-bought eggs in the shell will keep for 3 to 5 weeks in a home refrigerator at 40° Fahrenheit.  (This estimate assumes they have no cracks, are not kept in the refrigerator door, and have not been washed by the consumer.)  If the eggs are above 40° F for more than 2 hours, the USDA recommends they be discarded.  Egg cartons with the USDA grade shield will have a pack date printed on them, which is the day of the year, starting with January 1 = 1, on which the eggs were washed, graded and placed in the carton.  Many states also require a "Sell by" or "EXP" date on the carton.

Hard-boiled eggs do not keep as long as fresh eggs.

We receive many messages from readers unwilling or unable to take the U.S.D.A.'s advice.  Often, they want to know how long a freshly-laid, unrefrigerated egg will last.  There is no simple answer to this question. For them, here is the advice of a respected source from an earlier time:

To Determine the Freshness of Eggs

“From July to September a large number of eggs are packed, small ends down, in cases having compartments, one for each egg, and kept in cold storage. Eggs are often kept in cold storage six months and then sold as cooking eggs.”

Fannie Merritt Farmer.
Boston Cooking-School Cook Book, Revised Ed.
Boston: Little, Brown and Co., 1933.

Converting number of eggs in a recipe to other sizes

Printed recipes calling for a number of eggs generally assume Large eggs will be used. The chart below may be used to find the approximate equivalent in other sizes of a number of Large eggs. The percentage in parentheses is the percentage over or under the called-for weight of Large eggs that the given number of the other size will be.

If it is better to have more egg than too little:

Jumbo Extra-
Large
Recipe calls for Medium Small Peewee
1
(+25%)
1
(+13%)
1 2
(+75%)
2
(+50%)
2
(+25%)
2
(+25%)
2
(+13%)
2 3
(+31%)
3
(+13%)
4
(+25%)
3
(+25%)
3
(+13%)
3 4
(+17%)
4
(same)
5
(+4%)
4
(+25%)
4
(+13%)
4 5
(+9%)
6
(+13%)
7
(+9%)
4
(same)
5
(+13%)
5 6
(+5%)
7
(+5%)
8
(same)
5
(+4%)
6
(+13%)
6 7
(+2%)
8
(same)
10
(+4%)
6
(+7%)
7
(+13%)
7 8
(same)
10
(+7%)
12
(+7%)
7
(+9%)
8
(+13%)
8 10
(+9%)
11
(+3%)
13
(+2%)
8
(+11%)
8
(same)
9 11
(+7%)
12
(same)
15
(+4%)
8
(same)
9
(+1%)
10 12
(+5%)
14
(+5%)
16
(same)
9
(+2%)
10
(+2%)
11 13
(+3%)
15
(+2%)
18
(+2%)
10
(+4%)
11
(+3%)
12 14
(+2%)
16
(same)
20
(+4%)

If it is better to have less egg than too much:

Jumbo Extra-
Large
Recipe
calls for
Medium Small Peewee
1 1
(−13%)
1
(−25%)
1
(−38%)
1
(−38%)
1
(−44%)
2 2
(−13%)
2
(−25%)
3
(−6%)
2
(−17%)
2
(−25%)
3 3
(−13%)
4
(same)
4
(−17%)
3
(−6%)
3
(−16%)
4 4
(−13%)
5
(−6%)
6
(−6%)
4
(same)
4
(−10%)
5 5
(−13%)
6
(−10%)
8
(same)
4
(−17%)
5
(−6%)
6 6
(−13%)
8
(same)
9
(−6%)
5
(−11%)
6
(−4%)
7 8
(same)
9
(−4%)
11
(−2%)
6
(−6%)
7
(−2%)
8 9
(−2%)
10
(−6%)
12
(−6%)
7
(−3%)
8
(same)
9 10
(−3%)
11
(−8%)
14
(−3%)
8
(same)
8
(−10%)
10 11
(−4%)
13
(−3%)
16
(same)
8
(−9%)
9
(−8%)
11 12
(−5%)
14
(−5%)
17
(−3%)
9
(−6%)
10
(−6%)
12 13
(−5%)
15
(−6%)
19
(−1%)

How much of an egg is shell, yolk and egg white?

In Canada, 87% by weight is

How many eggs can a hen lay in a year?

153 as an extreme, 60 nonintensively.

For Further Reading

T. C. Carter.
Egg Quality: A Study of the Hen's Egg.
Edinburgh: Oliver and Boyd, 1968.

William J. Stadelman and Owen J. Cotterill, editors.
Egg Science and Technology. 3rd ed.
Westport, CT: Avi Publishing, 1986.

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