Food technologists Mike Musgrove and Deana Jones from the Poultry Processing and Meat Quality Research Unit of the USDA's Agricultural Research Service tested the quality and functionality of table eggs during a 10-week storage time, long beyond the current 30-day industry standard for storing eggs on the store shelf.
"Most eggs are sterile when formed, but may become contaminated as they exit the hen's body or from any surface they contact," said Musgrove, who tested the eggs for the presence of bacteria like Salmonella, Escherichia, Enterobacter, Klebsiella and Yersinia
If the eggs are handled or processed improperly, these bacteria can remain on the shell when they reach the consumer, but Musgrove found that current cleansing procedures were more than adequate at protecting consumers. Eggs are washed with water that is between 90°F and 120°F, then rinsed with hot water and chlorine before being placed in cold storage and shipped.
"Repeated testing of eggs after washing and packaging showed no Enterobacteriaceae bacteria contamination until the fifth week after processing. Fewer bacteria on the surface of the egg means fewer can get into the egg when they are cracked in preparation for consumption," Musgrove said.
The eggshell and membranes under it provide a barrier that limits the ability of organisms to enter the egg, he explained. The shell surface has from 7,000 to 17,000 tiny pores that permit moisture and carbon dioxide to move out and air to move in. A natural protective coating called the cuticle helps preserve freshness and prevent microbial contamination. But since this coating is damaged or removed by processing, a thin layer of oil is applied to preserve the egg's internal quality.
Eggs are found in a wide range of foods, including baked goods and mayonnaise, and it is often the chemical properties of the eggs which give these foods their distinctive properties. Over time, eggs can lose their ability to make mayonnaise creamy, but Jones' research showed that this did not happen at the usual 30-day sell-by date.
"During our study of egg functionality over 10 weeks of storage, we found no marked decrease in quality," she said. "Angel food cakes were light and fluffy using eggs stored up to 10 weeks."
So the current sell-by date for eggs should perhaps be considered as more of a starting point than an end one. "Egg quality isn't affected for quite a long time, which allows for storage beyond the sell-by date," said Jones, while Musgrove's data suggests that current US federal guidelines for producing and processing eggs mean that safety and quality can be ensured be even during long-term storage.