The debate over how to store shell eggs has been going on ever since the chicken laid the first egg, if we assume the former came before the latter. Our ancestors looked at a range of techniques to preserve eggs, from burying them in lime to coating them with sodium silicate (water glass). The methods were relatively effective, with more than a one-year shelf life being reported, although prolonged storage had negative effects on egg quality such as coagulating the white and imparting interesting flavors to the yolk.
The French went a step further in the 17th century by incorporating eggs into vinegar and oil to make the first mayonnaise, or into citrus fruit purée, which later evolved into lemon curd. The French can also be credited with introducing the trend of eating eggs with soft yolks, which, at the time, were considered to aid digestion. The tradition has been retained, and if you order any egg dish in France, be prepared to expect a practically raw yolk. Certainly eggs simply taste better when partially cooked, even though the risk of Salmonella exists.
To wash or not to wash? That is the question.
When the population moved into urban centers during the latter part of the 19th century, there was a need to transport foods over relatively large distances, and, moreover, look acceptable to the paying customer. When eggs are laid, there is a mucus layer around the outside of the shell that subsequently dries out to form the cuticle — a hard protein layer. At this time, the eggs can be contacted by dust, feathers, soil and manure, making the visual appearance undesirable to the paying consumer. Therefore, in the early 20th century, there was interest in washing eggs before sending them off to market.
In 1919, Jenkins was the first to report about the negative effect of egg washing, which led to “green whites,” along with “crusted yolks,” due to spoilage by pseudomonads. There were also anecdotes reported that washed eggs had a greater tendency to develop rots (for example, Aspergillus) compared to those that had not been washed. Brooks pulled all the evidence together in 1951 and came to the conclusion that egg washing caused more problems than it solved.
It was at this point the Europeans and North Americans went down very different paths, even though they based their decisions on the same set of data. Specifically, the Europeans took the works of Jenkins and Brooks to clearly show that washing eggs was not practical, cost-effective or beneficial. In contrast, the North Americans (USDA, specifically) concluded that the Europeans gave up too early, and, with a little tinkering with the equipment, could make the egg-washing process work.
The early egg washes of the 1950s were essentially washing machines where the eggs would be placed into hot water (49 degrees C, or about 120 degrees F), along with soap, then gently agitated for three minutes. The consequences of the wash process were to remove the protective cuticle layer and possibly cause fractures in the shell, leading to ingress of water along with the spoilage microbes.
USDA went to work on the problem and came up with new egg-washing technology and guidelines. In brief, the new wash process involved misting/fogging with pressure sprays being used to remove stubborn soils. Additional recommendations were to wash eggs soon after laying (before the cuticle dried), ensure that the iron content of water was kept below 2 ppm (to prevent membrane weakening), maintain sanitizer-detergent levels and apply an oil film to the post-washed egg. A further critical feature of the revamped wash process was to ensure that eggs were dried before packaging, then distributed/stored below 45 degrees F ( to minimize microbial growth). The revised washing method appeared successful in terms of reducing incidence of spoilage compared to the original wash process.
Meanwhile, back in Europe
The European policy on eggs was essentially based on a preventive approach by ensuring eggs were delivered to packing houses without visible dirt and also providing the option of dry brushing. Critically, egg washing was banned, and, as a further step, the recommended storage temperature was set at 62 to 73 degrees F to minimize the risk of condensation. The regulations also specified that the temperature fluctuation from delivery to the packing house, distribution and retail should be no more than 11 degrees F. Again, this was to avoid condensation that could facilitate the ingress of microbes from the shell into the inner egg. In effect, the regulation was interpreted as the correct storage temperature for eggs is room temperature.
Edwina Curry speaks
The 1980s was a decade when the food industry recognized that the practices developed in terms of efficiency had detrimental effects in terms of food. One relevant example was the practice of using ground chicken carcasses as poultry feed, along with other dubious practices. At this time there was an increase in the incidence of a virulent Salmonella Enteritidis that could transfer to the yolk prior to the egg being laid (transovarial transmission). The multi-drug resistant Typhimurium DT104 was also becoming established in poultry operations. The incidence of Salmonella in the UK was especially cause for concern as, toward the end of the 1980s, the number of cases had tripled in the space of two years. The egg industry simply turned a blind eye to the problem, and the Department of Agriculture & Food was glad to do the same.
Then, in December 1988, a junior minister in the Department of Health (one Edwina Curry) came out with the famous quote, “Most of the egg production in this country sadly is now infected with Salmonella.” The UK egg industry collapsed overnight, and, in less than a month, Curry was removed from office as her government colleagues turned on their own. History proved her right, although she didn’t actually know what the carriage of Salmonella in eggs was at the time and neither did the industry or the Ministry of Agriculture — if you don’t look, you don’t find.
In effect, Curry had made a slip by using “most” when she should have said “some.” Nonetheless, the horse had bolted from the stable, and the egg industry had to make amends. What emerged was the Lion Stamp, which essentially put in place Salmonella control interventions, the most notable being vaccinating poultry to reduce the incidence of Enteritidis and Typhimurium within the laying flock. In addition, a best-before date of 21 days was stamped on eggs based on the time it would take Salmonella to go from the surface to the internal structure of the egg, among other interventions.
At this time, the washing of eggs was revisited by the UK and Europe in general. The net conclusion of the study was that egg washing did represent an enhanced risk of introducing Salmonella into the inner egg due to the lack of protective cuticle layer and ingress of water. The report also noted that there were too many aspects of the wash process that could go wrong, along with the obvious issue of transoverian transmission of Enteritidis. Therefore, the Europeans did not see the need to change the policy on egg washing, and the ban was kept in place.
One problem encountered with storing eggs at room temperature was that the inner membrane and white of the egg degrade, leading to broken yolks when cracked into the frying pan. Therefore, a three-year project was undertaken to find the best way to store eggs to preserve quality while reducing the risk posed by Salmonella. The net result of the research was that eggs can be stored in the fridge provided they are kept in the carton (egg box) to minimize condensation on the shell surface.
So who has the right egg policy? U.S. vs. Europe
Through time, the European philosophy of foodborne pathogen control has been that prevention is better than the cure. The North American approach is more directed toward post-harvest interventions, given the difficulty in controlling pathogens at the primary production level. So the question arises: Did the North Americans take the right path with egg washing or is the European approach the way to go? Well, it really depends on what metrics are used to gauge success. In terms of Salmonella prevalence in flocks, the average in the EU is 2 percent, compared with 6.5 percent in the U.S. How about the prevalence of Salmonella in eggs? It is estimated that 1 in 10, 000 eggs carries Salmonella in the U.S.; in the EU, it’s 1 in 150, 000. Does such low carriage translate into a decrease in Salmonella cases? Yes, the incidence of Salmonella has significantly decreased in Europe.
All indicators would therefore suggest that the European egg policy has been more effective compared to that formulated by USDA. However, this doesn’t mean that outbreaks of Salmonellosis linked to eggs are a thing of the past in Europe. Indeed, in the summer of 2014, there was an outbreak linked to eggs resulting in more than 300 confirmed cases across Europe. The source of the contaminated eggs was traced to a German egg-packing plant. Although not on the same level as the U.S. Salmonellosis outbreak of 2010, the incident illustrates that any food safety system is only as strong as the weakest link.
It certainly would be too simplistic to suggest that washing has no value, as there is a reduction in the carriage of Salmonella on the shell, and, of course, it makes for a cleaner-looking egg. Still, the European approach to tackling pathogens on the farm rather than relying on post-harvest methods will ultimately be a more effective strategy. We are waking up to this fact in North America and clearly a vaccination program would go a long way to improve the microbiological safety of eggs irrespective of washing.© Food Safety News