The USDA has a webpage which explains what the four different types of expiration dates mean; from the page:
- A “Sell-By” date tells the store how long to display the product for sale. You should buy the product before the date expires.
- A “Best if Used By (or Before)” date is recommended for best flavor or quality. It is not a purchase or safety date.
- A “Use-By” date is the last date recommended for the use of the product while at peak quality. The date has been determined by the manufacturer of the product.
- “Closed or coded dates” are packing numbers for use by the manufacturer.
The page goes on to say that even for the use-by date, “a product should be safe, wholesome and of good quality if handled properly and kept at 40°F or below.” Things that have been continuously frozen are safe indefinitely. Otherwise, the USDA recommends to eat it by the use-by date, if the package has one, just because it’ll taste better, if nothing else. The safety issues come into play mainly when food is improperly handled, even if it’s before the use-by date. Improper handling can include leaving food out for several hours, thawing for more than two hours, contaminating it with something or being handled by filthy people. Foods should also pass the smell and look test: if it smells or looks funny, even if it’s not unsafe, it’s at least past its prime as far as quality goes.
For sell-by dates, on the other hand, the USDA provides a couple of charts (below) which indicate that uncooked poultry and processed meats can be kept for a day or two after bringing them home (regardless of the sell-by date), other uncooked meats for 3 to 5 days, cured ham for up to a week and eggs for up to 5 weeks. (It also goes into some detail on eggs with the USDA shield, which are stamped with the day of the year they were packed — 001 for January 1st, 179 for June 27, 365 for December 31st — and have to be sold 45 days after that. A calculator which converts dates into the day of the year is available at mistupid.com. Eggs should also be kept in the coldest part of the fridge, not the door.) Cooked meats that have been processed and packed at a plant can be kept for quite a while longer: at least a few days in the package, then another few days after opening.