Food Sell-By Dates: What They Really Tell You

— -- There are multiple ways to determine if that carton of milk in your fridge should be thrown out (smell test, taste test or just checking the "sell-by" date). But what's the best way to figure out if your food should be tossed or saved?

"Sell-by" dates may seem like an easy way to tell when to throw out food, but it turns out that in most cases, a "sell-by" or "best used by" date isn't an automatic warning sign that the food is spoiled.

According to the U.S. Department of Agriculture, the “sell-by” date tells the store how long to display the product for sale. It doesn’t mean the product has gone bad once it reaches the "sell-by" or "best used by" date.

A “best used by” date actually has nothing to do with spoilage. In this case, the date is recommended for flavor or quality standards. A canned item like soup with a “best if used by” date might be safe to eat long after the date passes, but expect a little less flavor with each passing day.

There are no federal requirements for putting expiration dates on food, except for infant formula. A “best used by” date indicates the last date of the product’s peak quality. In the case of infant formula, using a product after the “best used by” date can mean there are less nutrients and the quality may have degraded so that the formula separates or clogs.

Dr. Michael Hansen, senior staff scientist with Consumers Union, a consumer trade group, told ABC News that the dates listed on food don’t give much indication if a product has spoiled or not.

“What most people think is that the food is bad after that date,” Hansen said, "and that it could be a hazardous.”

The USDA has guidelines on how long to keep perishable items in the fridge here. The guidelines should be followed regardless of the “sell-by” date. Food with a "use-by" date shouldn't be consumed after that date passes.