Shell Eggs

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 properly 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. These all-in-one reproductive cells, incorporating the nutrients to support life, evolved about a billion years ago. The first eggs were hatched in the ocean. As animal life emerged from the water about 250 million years ago, they began producing an egg with a tough leathery skin to prevent dehydration of its contents on dry land. The chicken evolved only about 5,000 years ago from an Asian bird.

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?

People with health problems, the very young, senior citizens, and pregnant women (the risk is to the unborn child) 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 Marketing Service (AMS), 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. The interim goal of the Egg Safety Action Plan is a 50 percent reduction in egg-associated SE illnesses by 2005.

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. AMS visits shell egg handlers and hatcheries four times each year to ensure conformance with these requirements. 
  • The USDA grade mark on egg cartons means the plant processed the eggs following USDA's sanitation and good manufacturing processes. 
  • On April 27, 1998, AMS announced a prohibition on the repackaging of eggs 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 imported shell eggs from all countries. Due to AMS' expertise in these areas, AMS carries out these tasks on behalf of FSIS. 
  • 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 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.

National Agricultural Statistics Service (NASS)

  • USDA collects processing and distribution information for the economic analysis of the egg products industry through NASS.  

FSIS/FDA Cooperation

  • FSIS and the Food and Drug Administration (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 compliance with official U.S. standards, grades, and weight classes by egg packers not using the USDA/AMS shell egg grading service.  

State and Local Health Departments

  • State and local health departments monitor compliance with state and local health department requirements by food retail and foodservice establishments.  

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.  

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 to state 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.  

Can Shell Eggs Be Pasteurized?

Shell eggs can be pasteurized by a processor if FDA approves the process. Pasteurized shell eggs are available in some parts of the country, but are not yet available nationwide. Also, the equipment necessary to pasteurize eggs isn't available for home use, and it's not possible to pasteurize eggs in the home.  

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, and for any other purpose.     

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.   

Always purchase eggs before the "Sell-By" or "EXP" (expiration) 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. This date is not federally required, but may be State required.  

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. When the egg is laid, 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. Then the egg is coated with a tasteless, natural mineral oil to protect it.  

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. Don't wash eggs. That could remove the protective mineral oil coating and increase the potential for bacteria on the shell to enter the egg.  

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 hands, 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. Because the bread is kept at room temperature, these eggs should be considered a decoration only and not eaten.

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 Ukranian 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 chlorine bleach per half cup of water. After blowing out the egg, refrigerate the contents and use within 2 to 4 days; cook thoroughly before eating.   

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 until eaten.  

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
1950 389
1960 321
1970 311
1980 273
1990 236
1998 244
2000 260
2001 261

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. It forms as the egg cools, 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 unusable 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.  

Recommended Egg Resources

 Oster 4716 Egg Cooker 

 Nordic Ware Microwave Egg Cooker 

 International Playthings Hide'N Squeak Eggs 

 Meinl Plastic Egg Shaker (4 pc Assortment) 

 The Easter Egg by Jan Brett 

 Dr. Seuss's Beginner Book Collection (Cat in the Hat, One Fish Two Fish, Green Eggs and Ham,
Hop on Pop, Fox in Socks)

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 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.  

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 brined eggs -- marinated, hard-cooked eggs -- keep for several months on the shelf. After opening, keep refrigerated.  



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


10 days Do not freeze.


3 days Do not freeze.

Egg substitutes, frozen


After thawing, 7 days, or refer to "Use-By" date on carton. 12 months


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.


3 to 5 days 6 months


2 to 4 days Do not freeze.

pumpkin or pecan

3 to 4 days After baking, 1 to 2 months.

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.

For additional food safety information about meat, poultry, or egg products, call the toll-free USDA Meat and Poultry Hotline at 1-888-MPHotline (1-888-674-6854); for the hearing-impaired (TTY) 1-800-256-7072. The Hotline is staffed by food safety experts weekdays from 10 a.m. to 4 p.m. Eastern time. Food safety recordings can be heard 24 hours a day using a touch-tone phone.