Sunday, December 23, 2012

Should You Wash Your Eggs

As a matter of general practice, we've washed our eggs prior to placing them in the refrigerator.  We've also known that many other backyard chicken owners  do not wash their eggs because they believe they stay fresher when left in their natural state.  To determine the best practice, we reviewed some of the scientific literature on the subject and make a recommendation to readers of this blog.  

If you don't want to read the full post, skip to the end where we make our recommendation and provide what we believe to be practical advice to backyard chicken owners. 


Egg photo by Sun Ladder

Some Background About Eggs & Bacterial Contamination

Eggs are designed to limit the possibility of bacterial contamination. This makes intuitive sense because eggs must protect the chicken's embryo during incubation.  These  natural protections include:

  •  The shell - made from calcium carbonate, the shell functions like a ceramic container that acts as a hard barrier to bacteria. The shell also is made of proteins that are antimicrobial so the shell acts both as a mechanical and chemical barrier. Although the shell appears solid, it contains thousands of small pores that allow air to pass through the shell so that a chick embryo can survive. Unfortunately, these can be a doorway for bacteria to enter into the egg itself, so eggs are further protected by the following mechanisms....
  • The cuticle - During the last stage of egg formation, a layer of protein and carbohydrates is deposited on the surface of the shell before it passes out of the chicken's oviduct. The cuticle, sometimes called the bloom, "plugs" the pores in the egg shell and helps prevent bacteria from penetrating the egg. The cuticle still allows oxygen to pass into the egg, but provides a barrier that keeps the bacteria out. However, the effectiveness of the cuticle can be compromised.  Washing the surface of an egg may remove surface debris and bacteria, but it also reduces, or eliminates, the cuticle, the eggs natural protective cover for the pores. (More on this subject later when we discuss egg washing)
  • Egg Whites - the egg white, or albumen, provides a series of defenses against bacteria should it find its way into the egg through a pore.  The egg white inhibits the growth of bacteria because it does not contain sufficient nutritional value for bacteria to thrive. If bacteria enters the egg it has nothing to eat unless it gets to the yolk. Fortunately the white also is fairly viscous so it inhibits the bacteria's ability to move around. In sum, egg whites fight bacteria contamination by limiting their ability to get the the yolk and giving them little to eat when trapped in the albumen.
Cross section of an egg shell. Image from PoultryHub.org

Visually Clean Eggs Aren't Clean

While eggs are designed to protect their contents, it's important to recognize that the outside shell of the egg is not clean.  Chicken's eliminate waste from their body by excreting it from their intestines through an organ called the vent. This same vent is the door which is used when a chicken lays an egg. In this case, the egg passes from the chicken's oviduct and through the vent before being deposited in a nest box.

As you can imagine, using the same organ to pass waste and lay eggs has profound consequence for the cleanliness chicken eggs. Even eggs that look clean to the naked eye are contaminated by a layer of bacteria on their surface. Once in the nest box, eggs can pick up additional bacteria from mud, bedding or any other materials that are tracked into the nest box by the comings and goings of chickens.  Again, the shell and the cuticle protect the content of the eggs, but the surface of the egg above the cuticle is generally loaded with bacteria.


Chicken Reproductive System. Image from PoultryHub.Org


The Benefits of Washing Eggs

The primary reason to clean eggs is to remove the layer of bacteria that sits on the surface of the shell. This can significantly reduce health risks posed to humans:
  • If there's little bacteria on the shell surface, there's little bacteria that can penetrate into the egg if the shell is accidentally cracked or damaged prior to consumption. 
  • If there's little bacteria on the shell, there's a lower chance that humans will accidentally transfer that bacteria from the shell to other food when cooking.

Why Not Wash All Eggs?

So why not wash the eggs and get rid of this bacteria? As it turns out, it's not so easy to wash eggs properly. One can actually do more damage then good if eggs aren't washed and stored the right way. 

Washing removes much, but not all bacteria, and once the egg is washed the remaining bacteria have an opportunity to do increased damage because the protective cuticle is now compromised. Here's how it can happen; if an egg is washed in water that is colder than the egg itself, the interior contents of the egg contract. This causes a vacuum to form inside the egg that pulls water and any remaining bacteria on surface of the shell through the pores and into the interior of the egg. So eggs need to be washed under very specific temperature if they are to remain safe.

The process by which the eggs are washed is also important. In the past, commercial egg washing was done by immersing the eggs in a tank of water with detergents and sanitizers.  This method has been largely abandoned because it was discovered that the water could become highly contaminated and actually increase contamination by transferring bacteria through the wash water. 

Modern commercial systems wash eggs in an in-line process that is fairly complicated:


  • First, the eggs are lightly sprayed with warm water to loosen any droppings or debris on the surface.
  • Then, the eggs are moved on a conveyor to a washing station where they are washed using jets of water and brushes. The water temperature is controlled so that the water is at least 20 degrees Fahrenheit warmer than the temperature of the eggs themselves. This prevents the aforementioned problem of pulling bacteria from the surface of the shell into the egg. Current best practice is to wash at a temperature between 100 and 113 degrees Fahrenheit.  (Research suggests that above 113 degrees the temperature completely destroys the cuticle.)
  • The eggs are also washed in water that is low in soluble iron and with detergents and sanitizers that are recognized as safe and of a known pH. The iron content of the water turns out to be fairly important because some water will penetrate the shell during cleaning and if it is high in soluble iron, the iron can interfere with the albumen's natural ability to inhibit bacteria.
  • Next, the eggs are dried quickly with warm air to prevent bacteria from being carried into the egg by any moisture sitting on the surface of the shell as it cools.
  • Finally, the eggs are immediately transferred to a refrigerator for storage.
A commercial In-Line Egg Washing Machine


Why We Think Egg Washing Should Be Limited for Backyard Chicken Owners

In a commercial production environment where best practices are employed, washing eggs is a safe and effective method for preventing food borne illness.  However, achieving best practices is probably difficult, or impossible, for most backyard flock owners:
  • It's probably safe to assume that most of us don't have a good way to know or control the temperature coming out of our kitchen faucets. When cleaning eggs, backyard flock owners are really guessing that the temperature is right. As with all guesses, where going to get it right sometimes, but not every time. 
  • It's probably also safe to assume that you most of us don't know the iron content of our water. This is probably not a big issue for city folks using municipal water, but the same can't be said for folks in the country using well water. As mentioned earlier, iron that enters the albumen can lower the eggs natural defenses against bacteria.
  • It's also a safe bet to assume that egg cleaning materials -- sponge, brush etc. -- are not being monitored or cleaned regularly so they may can be an unexpected source of contamination.
  • Egg drying procedures are likely to also be lax or inconsistent. Backyard chicken owners may be placing eggs into the refrigerator before they are thoroughly dried. The moisture on the now unprotected shell can act as a conduit for any remaining bacteria to penetrate into the center of the now unprotected egg. Best practice would be to dry the eggs with a towel and then allow them to completely air dry before placing them in the refrigerator. 
While none of the above is impossible for the backyard chicken owners, we think that consistently implementing best practices is unlikely. As a result we've come around to the idea of washing only those eggs that clearly require it to remove large quantities of dropping and debris from the surface. Such eggs would be particularly unsanitary to place in the refrigerator unwashed. 



Pancake drinking from a BriteTap chicken waterer in our coop

Recommendations

Our recommendations for keeping your eggs safe are a combination of preventative measures and what we believe are pragmatic hygiene practices:
  • Keep bedding and nest boxes clean and free of mud and droppings to reduce large scale contamination.
  • Collect eggs at least once per day to prevent eggs shells from becoming cracked in the nest box and opening up places where bacteria can penetrate the interior of the egg.
  • Discard any eggs that are clearly cracked as they are highly susceptible to contamination.
  • Wash only those eggs that are contaminated by large quantities of dirt or droppings. By large quantities, we mean dirt and/or droppings on the shell surface that is clearly visible. 
  • Wash these eggs using a clean paper towel in water that feels hot to the touch but is not scalding. For perspective, the maximum recommended temperature to wash eggs is 113 degrees. Most people would find 130 degrees very uncomfortable, so use your senses to regulate the water temperature recognizing that your senses are a very imperfect tool. (By the way, hot water heaters in the U.S. are generally set at a temperature of 130-150 degrees Fahrenheit) 
  • Once the eggs are cleaned, immediately dry them with a paper towel. Make sure they are fully dry before placing them in storage cartons. 
  • On the other hand, refrain from washing eggs that look clean to the naked eye. As we stated above, all eggs pass through the a chicken's vent and pick up bacteria along the way. Clean looking eggs aren't really free of bacteria. However, we believe that the risks of damaging the egg shell or cuticle during cleaning, and thus introducing bacteria into the egg, is higher than just placing the egg into a carton unwashed. This is based on our assumptions regarding the the average persons ability to consistently wash eggs under "best practice conditions." Therefore, we don't recommend cleaning eggs unless they are so filthy that placing them in the refrigerator would pose a higher risk than than cleaning them.
  • When handling eggs, understand that the shell is contaminated and act accordingly. Wash your hands after handling eggs, particularly when preparing food that will be served uncooked as you can contaminate these foods after touching unwashed eggs.

We make these recommendations understanding that reasonable people can come to different conclusions.  In the United States, the USDA requires egg producers to wash eggs prior to sale. In most of Europe, the opposite is true. 

Let Us Know What You Think

Please leave a comment and let us know whether you currently wash your eggs. We'd also like to know if any of the information in this article will influence your current practice with regard to egg washing. 
_________________
Article posted by ChickenWaterer.com, manufacturer of the BriteTap chicken waterer.


Some sources to look at for more information:

Opinion of the Scientific Panel on Biological Hazards on the Request of the Commission Related to the Microbial Risks of Washing Table Eggs, The EFSA Journal 269, Sept 7, 2005.

Washing table eggs: a review of the scientific and engineering issues. M.L. Hutchinson et al., World Poultry Science Journal vol. 59, June 2003.

Small Scale Egg Handling, Anne Fanatico & Betsy Connor, National Sustainable Agriculture Information Service, 2009.








4 comments:

  1. Very good information.I have fallowed these guides over the years and think they very safe

    ReplyDelete
  2. Coming up we never refrigerated eggs so they only got washed before use.
    This is a very good article for the prose an cons.

    ReplyDelete
  3. Excellent information. Thanks for the guidelines at the end of the article, too. Yes, we already handle our eggs in this manner, but the reminder and explanations are always welcome.After four years, no problems so far. However, the recent discovery of rats on our property requires additional precautions with their food. Many thanis.

    ReplyDelete