Egg quality and safety

Egg safety – how to minimise the risk of getting sick

Eggs, like other protein foods such as meat, fish and poultry, can be contaminated with bacteria which, if allowed to grow, can cause food poisoning. This applies not only to dirty and cracked eggs but also to clean and uncracked eggs.

We often eat eggs raw or only lightly cooked in mayonnaises, aioli, caesar salad dressings, mousses, tiramasu, hollandaise sauce, soufflés etc. Such foods, along with eggs still in the shell, should be treated as though they were contaminated and should never be given to people with lowered immune systems. There have been a large number of documented outbreaks of Salmonella food poisoning from poorly handled eggs. In Australia these outbreaks are usually caused by consuming eggs raw or only lightly cooked.

Salmonella is the most common cause of food poisoning from eggs and is easy to destroy in cooking by heating until the temperature reaches 71 °C at the centre of the food. Where possible use a thermometer to be sure the food has reached this temperature.

Safety tips

A few simple steps will significantly reduce the risk of food poisoning from egg dishes.

Buy your eggs from supermarkets or shops which store them in the refrigerator or at least in a cool area of the store. Refrigerate your eggs immediately on arriving home - treat them like you treat your milk.
If you make dishes in which the eggs are only lightly cooked, such as some sauces and desserts, serve the food immediately or refrigerate. Don't let such food stand around at room temperature.
Never use dirty or cracked egg in foods that contain raw or only lightly cooked eggs.
Any egg nogs, mayonnaises, desserts etc containing raw eggs must be kept in the refrigerator until just before they are eaten.
Observe good personal hygiene when preparing food. Always thoroughly wash your hands before starting to prepare food and after handling raw foods.
Thoroughly clean and dry equipment and surfaces used to prepare raw egg dishes before reusing them to avoid contaminating other foods.
Reheat any egg containing leftovers to 74-75 °C (check with a food thermometer) before serving.
Avoid giving young children, the elderly, pregnant women and people with impaired immune systems foods containing raw or lightly cooked eggs.
If you keep hens and sell your excess eggs, make sure that you conform to any state regulations covering the sale of eggs. You may need to register with your local council (see further reading, below).

Egg freshness: what to look for

Eggs in the shell:

If you look closely at an egg shell held against a very bright light in a dark room you might be able to see an air gap, usually at the blunt end of the egg. In a fresh egg this air cell is quite small but as the egg ages, water is lost from the 17 000 or so pores in the shell and the air cell gets larger. If you hard boil an old egg, you can quite clearly see the air cell indentation in the top of the egg once you've taken the shell off.
Also you might see a large moving shadow in the egg which is the yolk floating about in the white. In fresh eggs the yolk is small, in the centre of the egg and not very mobile because the two strings of tissue that hold the yolk in place. These strings break down during storage. When you cut along a stale hard-boiled egg lengthways you will see that the yolk has moved off centre.
A quick test for freshness is to check if the raw egg in the shell sinks in a basin of water. Fresh eggs stay at the bottom of the bowl while stale eggs stand on end or float because of the large air cell. Other factors such as a weak shell and fine cracks can also cause the egg to float.

When broken out of the shell, good quality, fresh eggs display certain characteristics:

The yolk is small and rounded and stands high in a thick, gel-like egg white which tends to stay compact rather than spread out over a wide area. As eggs age, the yolk absorbs water from the white and becomes larger and flatter.
The thick egg white becomes thin and runny. By this time the egg might also have developed a stale odour and flavour.

Effects of freshness on egg performance:

As the egg ages and the white becomes thinner, it takes longer to whip into foam, the foam is less stable and collapses sooner.
Very fresh eggs with a lot of thick white do not foam well either as beaters have difficulty picking up the white. Once they have been beaten though the foam is more stable than in older eggs. Ideally eggs should be about three days old to obtain a maximum foam volume and stability.
Older eggs tend to spread when poached or fried because they are runnier. In very old eggs the membrane holding the yolk together is also likely to split as the egg is cracked open.
When boiling eggs, old eggs will show a large dent in the top because of the increased air pocket.

Eggs should be stored in cool conditions (less than 15° C) to maintain egg freshness and peak performance.

For long term storage

Control the temperature

Temperature, and to a lesser extent humidity, are the most important factors in maintaining egg freshness. The best way to keep eggs fresh is to store them in their cartons in the refrigerator as soon as possible after they are laid or purchased.
Eggs kept at room temperature can maintain their freshness for up to nine days after being laid, but the shelf-life will be shorter the higher the temperature.
Clean eggs, free of visible defects of the shell and contents, will remain fresh for six weeks from the date on the carton if stored in the carton in a refrigerator. They can still be used if stored for longer periods but the quality will begin to deteriorate.
The cartons reduce water loss and help prevent flavours from other foods from being absorbed into the eggs.
Avoid storing eggs loose as this increases the risk of damage which increases the opportunity for eggs to become unsafe.
Only clean, uncracked eggs in their shell should be stored.

Freezing raw eggs

Eggs can also be frozen as whole egg pulp, yolks or whites. To make sure that only sound eggs are used in foods containing raw egg or lightly cooked egg, label packages containing pulp from dirty or cracked eggs so that they are not accidentally used in these foods.
Freeze in small amounts of one or two eggs (about 55 g to 100 g).
Raw egg whites freeze well but yolks undergo gelation and when thawed are thick and gluggy.
Such yolks do not beat well and cakes and other products made from them are disappointing.
The problem can be overcome by lightly beating the yolks or whole eggs then adding one tablespoon of sugar or one teaspoon of salt to every six yolks or whole eggs before freezing.
Use the salted yolks in savoury dishes and the sugared yolks for cakes, custards and desserts.
Don't forget to label the packages as 'salty' or 'sweet'.
These should keep in the freezer for up to 10 months.

Oiling eggs

Where it is difficult to refrigerate or freeze raw eggs, a thin complete coating of mineral oil (e.g. paraffin or white oil) may be applied with a manual pressure spray (similar to that used to mist plants) to help preserve them. To have maximum benefit, eggs should be oiled the day they are laid.
Although on its own this is not as effective as refrigeration, oiling does slow down the loss of quality of the egg and if the eggs are then stored in a cool place you should obtain about three weeks of high quality life in most parts of Australia (in tropical regions you may only get about two weeks).
Only clean, sound eggs should be oiled.
Before boiling oiled eggs, prick the shells to allow the air to escape otherwise the eggs will crack open.

What to do with dirty or cracked eggs

Dirty and cracked eggs should be used immediately or frozen as pulp; they must never be sold. They should then only be used in thoroughly cooked foods such as biscuits and cakes or hard boiled for nine minutes or longer to ensure that any food poisoning bacteria that might have entered inside the egg are killed.
Eggs for in-shell storage in the home must not be washed as this removes the surface bloom and makes the eggs more susceptible to attack by bacteria. Unless correctly done, when washing faecally contaminated eggs, bacteria, including Salmonella, can be sucked into the egg.
Lightly soiled eggs can be cleaned with a clean, dry abrasive cloth.
Keep dirty or cracked eggs away from clean eggs to avoid contaminating them.
If you keep your own hens, regularly changing nesting materials and keeping nesting boxes away from roosting areas will help reduce the number of dirty eggs.

References

Braun P. 2000. Freshness of Table Eggs During Storage. World Poultry – Elsevier 16(10): 40-41.
HumphreyTJ, Greenwood M, Gilbert RJ, Rowe B. Chapman PA. 1989. The survival of salmonellas in shell eggs cooked under simulated domestic conditions. Epidem. Inf. 103: 35-45.
Sills VE. 1974. The Effect of Short-term Storage on the Albumen Quality of Shell Eggs. J. Sci. Fd Agric. 25 989-992.
Todd ECD. 1996. Risk assessment of use of cracked eggs in Canada. Int. J. Fd Micro. 30:125-143.

Quick links

Egg quality and safety

Egg safety – how to minimise the risk of getting sick

Safety tips

Egg freshness: what to look for

For long term storage

Control the temperature

Freezing raw eggs

Oiling eggs

What to do with dirty or cracked eggs

References

Further Reading

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