GOVERNMENT GUIDELINES.  What does the government say? The Food & Drug Administration, which regulates packaged foods and drugs, only requires a use-by, or expiration, date on infant formula. That's because formula must contain a certain quantity of each nutrient that is described on the label. And if formula is stored too long, it loses its nutritional quality, and also separates or form lumps that will clog the bottle nipple.

The Agriculture Dept., which regulates fresh produce and meats, only requires labeling of the date when poultry is packed at the farm. However, many manufacturers are allowed to also add sell-by or use-by dates. "Grocery stores that grind their own meat can add their own package labels," says USDA spokesman Steve Cohen.

In fact, both the FDA and the USDA have a pretty laissez-faire attitude when it comes to food shelf-life labeling. That's not because they are not concerned for people's health. Mark Harrison, professor of food science at the University of Georgia, points out that most of these dates are not an indicator of safety, rather of quality. "Some foods spoil if not refrigerated quickly enough—but they won't kill you," says Harrison.