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Shell Eggs from Farm to Table
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Eggs are among the most nutritious foods on earth and can be part of a healthy diet. However, they
are perishable just like raw meat, poultry, and fish. Unbroken, clean, fresh shell eggs may contain
Salmonella Enteritidis (SE) bacteria that can cause foodborne illness. While the number of
eggs affected is quite small, there have been cases of foodborne illness in the last few years. To
be safe, eggs must be safely handled, refrigerated, and cooked.
What is the History of the Egg?
"Eggs existed long before chickens," according to
On Food and Cooking: The Science and Lore of the Kitchen
by Harold McGee. "The first eggs were released, fertilized,
and hatched in the ocean. Around 250 million years ago, the
earliest fully land-dwelling animals, the reptiles, developed
a self-contained egg with a tough, leathery skin that prevented
fatal water loss. The eggs of birds, animals that arose some
100 million years later, are a refined version of this reproductive
adaptation to life on land. Eggs, then, are millions of years
older than birds. Gallus domesticus, the chicken more
or less as we know it, is only a scant 4 or 5 thousand years
old."
How Often Does a Hen Lay an Egg?
The entire time from ovulation to laying is about 25 hours. Then about 30 minutes later, the hen will
begin to make another one.
How Does Salmonella Infect Eggs?
Bacteria can be on the outside of a shell egg. That's because the egg exits the hen's body through the same
passageway as feces is excreted. That's why eggs are washed and sanitized at the processing plant.
Bacteria can be inside an uncracked, whole egg. Contamination of eggs may be due to bacteria within the hen's
ovary or oviduct before the shell forms around the yolk and white. SE doesn't make the hen sick. It is also possible
for eggs to become infected by Salmonella Enteritidis fecal contamination through the pores of the shells
after they're laid.
What Part Carries Bacteria?
Researchers say that, if present, the SE is usually in the yolk or "yellow." However, they
can't rule out the bacteria being in egg whites. So everyone is advised against eating raw or undercooked
egg yolks and whites or products containing raw or undercooked eggs.
What Safe Handling Instructions are on Egg Cartons?
All packages of raw, shell eggs not treated to destroy Salmonella must carry the following safe handling
statement:
SAFE HANDLING INSTRUCTIONS: To prevent illness from bacteria: Keep eggs refrigerated, cook eggs until yolks are
firm, and cook foods containing eggs thoroughly.
Who is "At Risk" for Eating Raw or Undercooked Eggs?
Infants, young children, older adults, pregnant women, and people
with weakened immune systems are particularly vulnerable to
SE infections. A chronic illness weakens the immune system,
making the person vulnerable to foodborne illnesses.
No one should eat foods containing raw eggs. This includes "health food" milk shakes made
with raw eggs, Caesar salad, Hollandaise sauce, and any other foods like homemade mayonnaise, ice cream,
or eggnog made from recipes in which the egg ingredients are not cooked. However, in-shell pasteurized eggs
may be used safely without cooking.
Who is Working on Eliminating the Salmonella in Eggs?
Federal and state governments, the egg industry, and the scientific community are working together to
solve the problem. Involved government agencies include: USDA's Food Safety and Inspection Service (FSIS),
Agricultural Research Service (ARS), and the Animal and Plant Health Inspection Service (APHIS); the U.S.
Food and Drug Administration (FDA); and State departments of agriculture.
Government agencies have implemented an Egg Safety Action Plan
to eliminate Salmonella Enteritidis illnesses due to
eggs. The Action Plan identifies the systems and practices that
must be carried out in order to meet the goal of eliminating
SE illnesses associated with the consumption of eggs by 2010.
What Government Agencies are Responsible for the Safety of Shell Eggs?
Many government agencies cooperate to ensure the safety of shell eggs from farm to table.
USDA Agencies
Agricultural Marketing Service (AMS)
- AMS administers a voluntary egg-quality grading program for shell eggs paid for by processing plants.
- AMS also is responsible for the Shell Egg Surveillance Program to assure that eggs in the marketplace are as good as or better than U.S. Consumer Grade B quality standards.
AMS conducts inspection of handlers and hatcheries four times each year to ensure conformance with these requirements.
Eggs exceeding the tolerance for checks or loss must be diverted from the marketplace for further segregation or processing.
- The USDA grade mark on egg cartons means the plant processed the eggs following USDA's sanitation and good manufacturing processes.
- Effective June 19, 2006, AMS announced final rulemaking prohibiting the repackaging of eggs previously shipped for retail sale that were packed under its voluntary grading program.
Animal and Plant Health Inspection Service (APHIS)
- APHIS conducts activities to reduce the risk of disease in flocks of laying hens.
- APHIS administers the voluntary National Poultry Improvement Plan (NPIP), which certifies that poultry breeding stock and hatcheries are free from certain diseases. Participation is necessary for producers that ship interstate or internationally.
- APHIS' National Animal Health Monitoring System is currently conducting a nationwide survey of the egg industry whose purpose is to estimate the national prevalence of SE layer flocks.
Food Safety and Inspection Service (FSIS)
- FSIS is responsible for the import of eggs destined for further processing and for
assuring that imported shell eggs destined for the retail market are transported under
refrigerated conditions.
- FSIS verifies shell eggs packed for the consumer are labeled
"Keep Refrigerated" and transported under refrigeration
and ambient temperature of no greater than 45 °F.
- USDA also educates consumers about the safe handling of
eggs. FSIS has developed numerous publications on egg safety
and uses a variety of networks (such as the USDA Meat and
Poultry Hotline, "Ask Karen," and USDA cooperative extension agents) to
get this information to consumers.
Agricultural Research Service (ARS)
- USDA also carries out food safety research through ARS and through a program administered by USDA's Cooperative State Research, Education & Extension Service (CSREES). Subjects include studying how Salmonella adheres to chicken cells, and developing an oral vaccine against SE.
- In 2005, ARS established the Egg Safety and Research Unit at the Russell Research Center in Athens, GA, to expand egg safety and egg processing research.
National Agricultural Statistics Service (NASS)
- USDA collects processing and distribution information for the economic analysis of the egg products industry through NASS.
Other Government Agencies
FSIS/FDA Cooperation
- FSIS and the FDA share authority for egg safety and are working together toward solving the problem of SE in eggs.
- FSIS and FDA are working to strengthen the Food Code and to encourage its adoption by States and local jurisdictions.
State Agriculture Departments
- State agriculture departments monitor for compliance of the official U.S. standards, grades, and weight classes by egg packers who do not use the USDA/AMS shell egg grading service.
State and Local Health Departments
- State and local health departments monitor retail food and foodservice establishments for compliance with state and local health department requirements.
What is Candling?
Candling is the process of using light to help determine the quality of an egg. Automated mass-scanning
equipment is used by most egg packers to detect eggs with cracked shells and interior defects. During candling,
eggs travel along a conveyor belt and pass over a light source where the defects become visible. Defective eggs are
removed. Hand candling—holding a shell egg directly in front of a light source—is done to spot check and
determine accuracy in grading. Advanced technology, utilizing computerized integrated cameras and sound wave technology,
is also being applied for the segregation of eggs.
How Are Eggs Transported Safely to Stores?
The U.S. Department of Commerce's 1990 Sanitary Food Transportation Act requires that vehicles be dedicated
to transporting food only. On August 27, 1999, FSIS made effective a new rule requiring:
- Shell eggs packed for consumers be stored and transported under refrigeration at an ambient (surrounding) air temperature not to exceed 45 °F;
- All packed shell eggs be labeled with a statement that refrigeration is required; and
- Any shell eggs imported into the United States, packed for consumer use, include a certification that they have been stored and transported at an ambient temperature of no greater than 45 °F.
What Is Included Under the Egg Products Inspection Act?
The term "egg products" refers to eggs that have been removed from their shells for processing
at facilities called "breaker plants." The safety of these products is the responsibility of FSIS.
Basic egg products include whole eggs, whites, yolks, and various blends—with or without non-egg
ingredients—that are processed and pasteurized. They may be available in liquid, frozen, and dried
forms. Most are not available in supermarkets, but are used in restaurants, hospitals, and other foodservice
establishments as well as by bakers, noodle makers, and other food manufacturers.
Egg products are pasteurized. The 1970 Egg Products Inspection Act (EPIA)
requires that all egg products distributed for consumption be pasteurized. They are rapidly heated and held at a minimum required temperature
for a specified time. This destroys Salmonella, but it does not cook the eggs or affect their color, flavor,
nutritional value, or use. Dried eggs are pasteurized by heating in the dried form.
While inspected pasteurized egg products are used to make freeze-dried egg products, imitation egg products, and egg
substitutes, these products are not covered under the EPIA and are under FDA jurisdiction. No-cholesterol egg substitutes
consist of egg whites, artificial color, and other non-egg additives. Direct questions about egg substitutes to the
manufacturer or to the FDA. For more information about egg products, read "Egg Products and Food Safety"
(https://webarchive.library.unt.edu/eot2008/20081004064510/http://www.fsis.usda.gov/Fact_Sheets/ Egg_Products_and_Food_Safety/index.asp).
Can Shell Eggs Be Pasteurized?
Shell eggs can be pasteurized by a processor if FDA approves
the process. Pasteurized shell eggs are now available at some
grocery stores. Like all eggs, they must be kept refrigerated.
The equipment to pasteurize shell eggs isn't available for home
use, and it is not possible to pasteurize shell eggs at home
without cooking the contents of the egg.
Are Powdered Egg Whites Pasteurized?
Yes. Egg white powder is dried egg white (pure albumen). It can be reconstituted by mixing the powder
with water. The reconstituted powder whips like fresh egg white and, because it is pasteurized, can be used
safely without cooking or baking it. The product is usually sold along with supplies for cake baking and
decorating.
What Points Should You Consider When Buying Eggs?
Always purchase eggs from a refrigerated case. Choose eggs with clean, uncracked shells. Don't buy out-of-date
eggs. Look for the USDA grade shield or mark. Graded eggs must meet standards for quality and size. Choose the size
most useful and economical for you.
Is Grading of Eggs Mandatory?
USDA's grading service is voluntary; egg packers who request it, pay for it. The USDA grade shield on
the carton means that the eggs were graded for quality and checked for weight (size) under the supervision of
a trained USDA grader. Compliance with quality standards, grades, and weights is monitored by USDA. State agencies
monitor compliance for egg packers who do not use the USDA grading service. These cartons will bear a term such
as "Grade A" on their cartons without the USDA shield.
What Are Egg Grades?
There are three consumer grades for eggs: U.S. Grade AA, A, and B. The grade is determined by the interior
quality of the egg and the appearance and condition of the egg shell. Eggs of any quality grade may differ in
weight (size).
- U.S. Grade AA eggs have whites that are thick and firm; yolks that are high, round, and practically free from defects; and clean, unbroken shells. Grade AA and Grade A eggs are best for frying and poaching where appearance is important.
- U.S. Grade A eggs have characteristics of Grade AA eggs except that 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.
Sizing of Eggs
Size tells you the minimum required net weight per dozen eggs. It does not refer to the dimensions
of an egg or how big it looks. While some eggs in the carton may look slightly larger or smaller than the
rest, it is the total weight of the dozen eggs that puts them in one of the following classes:
Size or Weight Class |
Minimum net weight per dozen |
Jumbo |
30 ounces |
Extra Large |
27 ounces |
Large |
24 ounces |
Medium |
21 ounces |
Small |
18 ounces |
Peewee |
15 ounces |
Dating of Cartons
Many eggs reach stores only a few days after the hen lays them.
Egg cartons with the USDA grade shield on them must display
the "Pack date" (the day that the eggs were washed,
graded, and placed in the carton). The number is a three-digit
code that represents the consecutive day of the year (the "Julian
Date") starting with January 1 as 001 and ending with December
31 as 365. 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 pack.
Use of either a "Sell-by" or "Expiration"
(EXP) date is not federally required, but may be State required,
defined by the egg laws in the State where the eggs are marketed.
Some State egg laws do not allow the use of a "Sell-by"
date. Always purchase eggs before the "Sell-by" or
"EXP" date on the carton.
After the eggs reach home, they may be refrigerated 3 to 5 weeks from the day they are placed in the refrigerator.
The "sell-by" date will usually expire during that length of time, but the eggs are perfectly safe to use.
Why Should Eggs Be Refrigerated?
Temperature fluctuation is critical to safety. With the concern about Salmonella, eggs gathered
from laying hens should be refrigerated as soon as possible. After eggs are refrigerated, they need to stay
that way. A cold egg left out at room temperature can sweat, facilitating the growth of bacteria. Refrigerated eggs
should not be left out more than 2 hours.
Should You Wash Eggs?
No. It's not necessary for consumers to wash eggs. When the
chicken lays the egg, a protective coating is put on the outside
by the hen. At the plant, government regulations require that
USDA-graded eggs be carefully washed and sanitized using special
detergent.
Why Do Hard-Cooked Eggs Spoil Faster than Fresh Eggs?
When shell eggs are hard cooked, the protective coating is washed away, leaving bare the pores in the
shell for bacteria to enter and contaminate it. Hard-cooked eggs should be refrigerated within 2 hours of
cooking and used within a week.
Safe Storage in Stores
At the store, choose Grade A or AA eggs with clean, uncracked shells. Make sure they've been refrigerated
in the store. Any bacteria present in an egg can multiply quickly at room temperature. When purchasing egg products
or substitutes, look for containers that are tightly sealed.
Bringing Eggs Home from the Store
Take eggs straight home and store them immediately in the refrigerator
set at 40 °F or below. Keep them in their carton and place
them in the coldest part of the refrigerator, not in the door.
Is It Safe to Use Eggs That Have Cracks?
Bacteria can enter eggs through cracks in the shell. Never purchase cracked eggs. However, if eggs crack
on the way home from the store, break them into a clean container, cover it tightly, keep refrigerated, and
use within 2 days. If eggs crack during hard cooking, they are safe.
How Are Eggs Handled Safely?
Proper refrigeration, cooking, and handling should prevent most egg-safety problems. Persons can enjoy
eggs and dishes containing eggs if these safe handling guidelines are followed:
- Wash utensils, equipment, and work areas with hot, soapy water before and after contact with eggs.
- Don't keep eggs out of the refrigerator more than 2 hours.
- Raw eggs and other ingredients, combined according to recipe directions, should be cooked immediately or refrigerated and cooked within 24 hours.
- Serve cooked eggs and dishes containing eggs immediately after cooking, or place in shallow containers for quick cooling and refrigerate at once for later use. Use within 3 to 4 days.
Are Easter Eggs Safe?
Sometimes eggs are decorated, used as decorations, and hunted at Easter. Here are some safety tips for Easter eggs.
- Dyeing eggs: After hard cooking eggs, dye them and return them to the refrigerator within 2 hours. If eggs are to be eaten, use a food-safe coloring. As with all foods, persons dyeing the eggs should wash their hands before handling the eggs.
- Decorations: One Easter bread recipe is decorated with dyed, cooked eggs in the braided bread. After baking, serve within 2 hours or refrigerate and use within 3 to 4 days.
- Blowing out eggshells: Because some raw eggs
may contain Salmonella, you must use caution when
blowing out the contents to hollow out the shell for decorating,
such as for Ukrainian Easter eggs. Use only eggs that have
been kept refrigerated and are uncracked. To destroy bacteria
that may be present on the surface of the egg, wash the
egg in hot water and then rinse in a solution of 1 teaspoon
liquid chlorine bleach per half cup of water. After blowing
out the egg, refrigerate the contents and use within 2 to
4 days.
- Hunting Eggs: Hard-cooked eggs for an egg hunt must be prepared with care to prevent cracking the shells. If the shells crack, bacteria could contaminate the inside. Eggs should be hidden in places that are protected from dirt, pets, and other sources of bacteria. The total time for hiding and hunting eggs should not exceed 2 hours. The "found" eggs must be re-refrigerated and eaten within 7 days of cooking.
Does the Color of the Shell Affect the Egg's Nutrients?
No. The breed of the hen determines the color of her eggs.
Araucuna chickens in South America lay eggs that range in color from medium blue to medium green.
Nutrition claims that araucuna eggs contain less cholesterol than other eggs haven't been proven.
Are Fertilized Eggs More Nutritious?
No. There is no benefit in eating fertilized eggs. There is no nutritional difference in fertilized eggs and infertile eggs. Most eggs sold
today are infertile; roosters are not housed with the laying hens. If the eggs are fertile and cell development is detected during
the candling process, they are removed from commerce.
Per Capita Consumption
Egg consumption in America was on a 40-year downward slide until the 1990's. Then eggs became increasingly
popular. The following figures are from USDA's Economic Research Service.
Year |
Eggs per
Person |
2004 |
256 |
1990 |
236 |
1950 |
389 |
Is the Appearance of Eggs Related to Food Safety?
Sometimes, but not usually. Variation in egg color is due to many factors.
- Blood spots are caused by a rupture of one or more small blood vessels in the yolk at the time of ovulation. It does not indicate the egg is unsafe.
- A cloudy white (albumen) is a sign the egg is very fresh. A clear egg white is an indication the egg is aging.
- Pink or iridescent egg white (albumen) indicates spoilage due to Pseudomonas bacteria. Some of these microorganisms—which produce a greenish,
fluorescent, water-soluble pigment—are harmful to humans.
- The color of yolk varies in shades of yellow depending upon the diet of the hen. If she eats plenty of yellow-orange plant pigments, such as from marigold petals
and yellow corn, the yolk will be a darker yellow than if she eats a colorless diet such as white cornmeal. Artificial color additives are not permitted in eggs.
- A green ring on a hard-cooked yolk is a result of overcooking, and is caused by sulfur and iron compounds in the egg reacting on the yolk's surface. The green color can also be caused by a high amount of iron in the cooking water. Scrambled eggs cooked at too high a temperature or held on a steam table too long can also develop a greenish cast. The green color is safe to consume.
How Do Time and Refrigeration Affect Egg Quality?
The egg, as laid at 105 °F, normally has no air cell. As the egg cools, an air cell forms usually in the
large end of the egg and develops between the two shell membranes. The air cell is formed as a result of
the different rates of contraction between the shell and its contents.
Over time, the white and yolk of an egg lose quality. The yolk absorbs water from the white. Moisture
and carbon dioxide in the white evaporate through the pores, allowing more air to penetrate the shell, and
the air cell becomes larger. If broken open, the egg's contents would cover a wider area. The white would be
thinner, losing some of its thickening and leavening powers. The yolk would be flatter, larger and more easily
broken. The chalazae (kah-LAY-zuh), the twisted cord-like strands of egg white that anchor the yolk in the center
of the white, would be less prominent and weaker, allowing the yolk to move off center. Refrigeration slows the loss of
quality over time.
What Does It Mean When an Egg Floats in Water?
An egg can float in water when its air cell has enlarged sufficiently to keep it buoyant. This means
the egg is old, but it may be perfectly safe to use. Crack the egg into a bowl and examine it for an off-odor
or unusual appearance before deciding to use or discard it. A spoiled egg will have an unpleasant odor when you
break open the shell, either when raw or cooked.
Safe Cooking Methods
Many cooking methods can be used to cook eggs safely including poaching, hard cooking, scrambling, frying and
baking. However, eggs must be cooked thoroughly until yolks are firm. Scrambled eggs should not be runny.
Casseroles and other dishes containing eggs should be cooked to a safe minimum internal temperature of 160 °F.
Use a food thermometer to be sure.
Use Safe Egg Recipes
Egg mixtures are safe if they reach 160 °F, so homemade
ice cream and eggnog can be made safely from a cooked egg-milk
mixture. Heat it gently and use a food thermometer.
- Dry meringue shells are safe. So are divinity candy and
7-minute frosting, made by combining hot sugar syrup with
beaten egg whites. Avoid icing recipes using uncooked eggs
or egg whites.
- Meringue-topped pies should be safe if baked at 350 °F
for about 15 minutes. Chiffon pies and fruit whips made
with raw, beaten egg whites cannot be guaranteed to be safe.
Instead, substitute pasteurized dried egg whites, whipped
cream, or a whipped topping.
- To make a recipe safe that specifies using eggs that aren't
cooked, heat the eggs in a liquid from the recipe over low
heat, stirring constantly, until the mixture reaches 160
°F. Then combine it with the other ingredients and complete
the recipe.
- To determine doneness in egg dishes such as quiche and
casseroles, the center of the mixture should reach 160 °F
when measured with a food thermometer.
- Use pasteurized eggs or egg products when preparing recipes
that call for using eggs raw or undercooked.
What Makes Hard-Cooked Eggs Hard to Peel?
The fresher the egg, the more difficult it is to peel after hard cooking. That's because the air cell, found at the large
end of the shell between the shell membranes, increases in size the longer the raw egg is stored. As the contents of the
egg contracts and the air cell enlarges, the shell becomes easier to peel. For this reason, older eggs make better
candidates for hard cooking.
What Are Thousand-Year-Old Eggs?
These Chinese eggs are not really 1,000 years old, but are somewhere between a month and several
years old. The egg is not retained in its original state, but rather converted into an entirely
different food, probably by bacterial action. They are exempt from inspection and grading. The
following are several types of thousand-year-old Chinese eggs.
"Hulidan" results when eggs are individually coated with a mixture of salt and wet clay or
ashes for a month. This process darkens and partially solidifies the yolks, and gives the eggs a salty taste.
"Dsaudan" eggs are packed in cooked rice and salt for at least 6 months. During this time, the shell
softens, the membranes thicken, and the egg contents coagulate. The flavor is wine-like.
"Pidan," a great delicacy, is made by covering eggs with lime, salt, wood ashes, and a tea
infusion for 5 months or more. The egg yolks become greenish gray and the albumen turns into a coffee-brown
jelly. Pidan smell ammonia-like and taste like lime.
Do Pickled Eggs Keep a Long Time?
Pickled eggs are hard-cooked eggs marinated in vinegar and pickling spices, spicy cider, or juice from pickles or
pickled beets. Studies done at the American Egg Board substantiate that unopened containers of commercially pickled eggs
keep for several months on the shelf. After opening, keep refrigerated and use within 7 days. Home-prepared pickled
eggs must be kept refrigerated and used within 7 days. Home canning of pickled eggs is not recommended.
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Egg Storage Chart |
Product |
Refrigerator |
Freezer |
Raw eggs in shell |
3 to 5 weeks |
Do not freeze. |
Raw egg whites |
2 to 4 days |
12 months |
Raw egg yolks |
2 to 4 days |
Yolks do not freeze well. |
Raw egg accidentally frozen in shell |
Use immediately after thawing. |
Keep frozen; then refrigerate to thaw. |
Hard-cooked eggs |
1 week |
Do not freeze. |
Egg substitutes, liquid Unopened |
10 days |
Do not freeze. |
Egg substitutes, liquid Opened |
3 days |
Do not freeze. |
Egg substitutes, frozen Unopened |
After thawing, 7 days, or refer to "Use-By" date on carton. |
12 months |
Egg substitutes, frozen Opened |
After thawing, 3 days, or refer to "Use-By" date on carton. |
Do not freeze. |
Casseroles made with eggs |
3 to 4 days |
After baking, 2 to 3 months. |
Eggnog, commercial |
3 to 5 days |
6 months |
Eggnog, homemade |
2 to 4 days |
Do not freeze. |
Pies, pumpkin or pecan |
3 to 4 days |
After baking, 1 to 2 months. |
Pies, custard and chiffon |
3 to 4 days |
Do not freeze. |
Quiche with any kind of filling |
3 to 4 days |
After baking, 1 to 2 months. |
Last Modified:
August 20, 2008 |
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