These days, absolutely every product seems to come with an expiration date - not just milk or meat, but even beer!

With all this extra information, it can be confusing for us consumers. Does "sell by" mean you have to toss the food after that date? Does "best if consumed by" mean it would actually be bad for you to eat the product after that date - or just that maybe the product would no longer be at the peak of its quality?

Now a couple of scientists with the Agricultural Research Service have cracked part of the puzzle, at least where eggs are concerned.

These scientists, based in Athens, Ga., tested how eggs taste and how well they "work" during 10 weeks of storage, which is far beyond the current 30-day standard for keeping eggs on the store shelf. The good news: While proper refrigeration and handling of the eggs is a must, the scientists didn't see a big drop in the eggs' quality during the entire 10 weeks!

One thing the scientists looked for was a family of bacteria called Enterobacteriacaea. That family name may not be familiar to you, but some of the "relatives" probably ring a bell: Salmonella, Escherichia (as in Escherichia coli), Enterobacter, Klebsiella, and Yersinia.

All of these bacterial "bad guys" can contaminate eggshells, and if the eggs aren't handled or processed properly, the bacteria can still be sitting on the eggshells when you the consumer bring those eggs home. Eggs are actually sterile when they're formed inside the hen, but they can become contaminated as they come out of the hen's body, or from touching any contaminated surface. Fortunately for us consumers, the cleansing procedures that commercial eggs go through generally take care of those unfriendly bacteria. (For the record, the eggs are washed with water between 90 and 120 degrees F, rinsed with hot water and chlorine, then placed in cold storage and shipped.)

In the 10 weeks of tests by the ARS scientists, repeated testing of eggs after washing and packaging showed no contamination by the bacteria until the fifth week after processing. And of course, fewer bacteria on the eggshell means fewer bacteria can jump inside once you crack that egg.

Mother Nature's given us a little assist on food safety when it comes to eggs; the eggshell and that filmy membrane just beneath the shell provide a natural barrier to limit the ability of organisms to get into the egg. Also, while the shell itself has as many as 17,000 tiny holes (called pores) that let moisture and carbon dioxide move in and out of the egg, the egg also has a natural protective coating called the cuticle that helps keep the egg fresh and fends off microbial contamination. But when the egg is commercially processed for marketing, this coating is damaged or removed, so typically a thin layer of oil is applied to the eggshell to help protect the internal quality.

Eggs are obviously an important part of many products, from baked goods to mayonnaise. But it stands to reason that an "old" egg might lose some of its chemical capacity to do everything we might want an egg to do - for example, fluff up an angel food cake. The question is, does that happen by the "sell by" date?

The ARS scientists say "no." They actually made angel food cakes with eggs that had been stored up to 10 weeks, and they reported full fluffiness. And if you're cooking eggs, the heat from the cooking will kill any bacteria that might have gotten a toehold in the egg during that 10-week period.

So what are we to make of that "sell-by" date? The bottom line is, you can keep and use those eggs for quite a while longer - no need to toss out perfectly good eggs or even rush to use them up within a few days of the "sell-by" date. And based on what the ARS scientists saw, it looks as though the current federal guidelines for producing and processing eggs have a beneficial effect on helping combat microbial contamination, even during long-term storage - so enjoy!

The Agricultural Research Service is the chief in-house scientific research agency of the U.S. Department of Agriculture. You can read more about ARS discoveries at (

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