The Life of an Egg

• Once a chicken lays her eggs, the clock begins to tick on their shelf life. Commercially produced eggs are cleaned and packaged before being stored at just below 45 degrees Fahrenheit to maintain their freshness, according to the U.S. Department of Agriculture. The date that the eggs are packaged is printed on the outside of the carton, along with a sell-by date. This date is a guide for a seller to follow to determine whether to keep the eggs on the shelf. While eggs can last a few weeks after this date, the market that sells them won't keep them on the shelf past this date.

Humpty Dumpty Had a Great Fall

• While the sell-by date lets a retailer know when to pull a carton of eggs from the shelf, if the eggs become damaged before this date, the seller removes them early. The shell of the egg contains calcium carbonate, which helps protect the contents of the egg from spoilage microorganisms and from drying out. This shell, along with a layer of protein that covers it, keeps the egg fresh. If the egg shell breaks or is otherwise damaged, the seller has to remove the entire carton of eggs from the shelf because the broken egg will spoil and become unusable by a consumer.

Eggs Keeping Their Cool

• After being laid by a hen, eggs should be kept refrigerated at 45 F or below within 36 hours to maintain their freshness and extend their shelf life, recommends the USDA. If the eggs remain at temperatures above 45 F for more than two hours, the store should remove them from the shelf. Without refrigeration, the shelf life of eggs is greatly reduced and they could be unsafe to eat. This means that eggs transported to the store from a farm also require constant refrigeration; otherwise, the store should not put them on the shelves for sale.

Spy Before You Buy

• While ideally a retailer should check eggs for freshness before selling them, sometimes this may not happen. Before you purchase your eggs, gently open the carton and check the eggs for cracks. If you notice that one or more of the eggs has an unpleasant smell, they've likely gone bad and you shouldn't purchase them. Alert a salesperson in the store if you notice eggs that have spoiled or if the carton is past its sell-by date. Some packages may have a "use by," date which is around 45 days after initial packaging; stores shouldn't sell eggs past this date either.