DEAR DR. BLONZ: Can you tell me how long eggs are still usable, after the best-by date on the carton? Are they safe to use in recipes? What about eggs purchased at a farmers' market, where there is no date on the carton? -- T.D., Lafayette, California
DEAR T.D.: Eggs that have a U.S. Department of Agriculture grading need to display the day of the year (from 1 to 365) on which the eggs were packed. Egg cartons often display an expiration date, as well -- the month and day after which they can no longer be sold, but are still safe to eat. Assuming they have been under refrigeration, you have about four to five weeks after the pack date during which the eggs are considered fresh and safe.
The expiration date will pass during this period. If purchasing eggs at a farmers' market, be sure to ask the vendor for the pack date. It is likely that there will be a dating system on any container for a perishable item such as eggs. Then make sure you note this date (or the date you purchased the eggs) on the carton you take home.
As time passes, eggs will gradually lose some of their qualities. In a fresh egg, the yolk is compact and stands high, and the white stays close to the yolk. As the weeks pass, the yolk and the egg white begin to spread, and the yolk sac becomes more fragile. Anyone who eats eggs sunny-side-up or over easy will notice that it doesn't take much to rupture the yolk of an older egg. These are the results of subtle changes in the egg albumin, the protein in the egg, but this does not have a significant impact on the egg's nutritional value. Over time, though, these changes can affect how an egg performs in certain recipes.
Use the freshest eggs for poaching or frying, as older ones will be more runny. If you want your egg to be whipped for volume, such as in a meringue or a cake, it's OK to use a "middle-aged" egg. Older eggs will perform fine if they are going to be used in a batter. If you are making hard-boiled eggs, older ones are preferred, as it is easier to take the shell off an older egg than a fresh one.
If the expiration date is long gone and you have concerns, it is always best to discard the eggs. If you do end up using eggs near, or just after, their expiration date, be sure to cook them well. That is always the best way to eliminate any bacteria that might have taken up residence. The USDA has a booklet on how to buy eggs, and there is more detailed information at eggsafety.org.
Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to firstname.lastname@example.org. Due to the volume of mail, personal replies cannot be provided.