"Use by" dates listed on food packaging don't necessarily mean a product has become unsafe to eat.

Q: Do I really need to throw out all types of food when it hits the expiration date?

A: It depends on what type of date is listed and where you store the products, according to Kathleen Glass at UW-Madison’s Food Research Institute.

The three main phrases used for dates listed on products are “use by,” “best by” and “sell by,” and those are for quality purposes, not safety, unless it is on infant formula, according to the U.S. Department of Agriculture.

“Best by” and “use by” mean about the same thing. The dates listed with those phrases mean that the product will no longer be at its best quality. The flavors may have changed, but it doesn’t mean a product is hazardous.

Glass said foods with “best by” listed before the date are typically for foods that many consider non-perishable, but those can still go bad from elements of the food like fat deteriorating. “Use by” dates are listed on foods that may spoil because of microbes.

“Spoiled foods will develop an off odor, flavor or texture due to naturally occurring spoilage bacteria,” the USDA said. If spoilage is evident, it should be thrown out.

“Sell by” dates, Glass said, are often listed for when a product still has about five to seven days before it spoils.

“Regardless, it is essential that the consumer check the storage conditions, too,” Glass said. “‘Keep refrigerated’ (labels are) intended to be 40 (degrees) or less for the duration of the shelf life.”

Glass said she keeps her refrigerator two or three degrees colder to maintain a longer shelf life.

Foods that have a “refrigerate after opening” label are used to warn consumers that it could be contaminated by microbes after opening, and refrigeration will prevent fast spoilage.

— Shelley K. Mesch

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