DEAR DR. BLONZ: Eggs have freshness dates on the carton, but how long are they safe to use after this date? Also: What are your thoughts about washing eggs once you get them home? And how long do hard-boiled eggs safely keep? -- S.T., Peoria, Illinois
DEAR S.T.: Eggs are an excellent source of high-quality protein (mainly in the egg whites). They also have B vitamins, including choline, a nutrient recently deemed essential that plays a role in cell function and neurotransmitters.
When eggs have a U.S. Department of Agriculture grade shield, they need to display the day of the year on which they were packed (numbered from 1 to 365). If a carton has both a sell-by date and a USDA grade, that date cannot typically exceed 30 days from the pack date. However, freshness dating regulations differ from state to state. (Read more on egg grading at b.link/ne29gm, on egg laws by state at b.link/557cev, and on USDA freshness dating at b.link/cbsr87.) Assuming the eggs have been under constant refrigeration, they are considered fresh and safe for about four to five weeks after the pack date. The expiration date, if one is provided, will pass during this period.
A good rule of thumb is to use fresh eggs within three to five weeks after purchase. Store eggs in the coldest part of the refrigerator, in their original carton. It is best to avoid the plastic egg-storage cups in some fridge doors; using them exposes eggs to refrigerator odors and temperature variances, as the door repeatedly gets opened and closed.
It is not recommended that you wash USDA-graded eggs once you get home. As a hen lays an egg, it deposits a coating, referred to as a bloom or cuticle, on the shell to protect against bacterial penetration through the shell's pores. Government regulations require that USDA-graded eggs be carefully washed and sanitized before being packed at the egg processing plant. Sanitization is done with food-grade substances; if eggs are certified organic, all substances used would meet those requirements. Washing these eggs can actually increase the risk of contamination because you remove the benefits of the prior wash/sanitization, and the wash water -- and unwanted stuff in it -- can be "sucked" into the egg through the more-vulnerable pores in the shell.
When shell eggs are hard-cooked, the protective coating gets washed away, leaving bare the shell pores for bacteria or odors to enter. Keep hard-cooked eggs in a sealed container and use them within about a week.
Send questions to: "On Nutrition," Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.