Is this food still good?

It's a topic that, in many households, is worthy of calling in an expert in arbitration: expiration dates on food packaging. Put a person who considers them gospel in the same kitchen with someone who views them as a rule of thumb and you'll definitely find a conflict in need of resolution.

So who's right? Well, you're not going to like this, but both are. Much depends on the specific food product in question and how it has been handled.

But first, a brief primer.

"There's a misunderstanding of what those dates stand for," said Christine Bergman, associate dean of the Harrah College of Hotel Administration at the University of Nevada, Las Vegas, whose doctoral degree is in food science. "Those dates are really there for food-quality purposes and not safety."

And the difference between food safety and food quality is something to remember. The latter, Bergman said, refers to a food's sensory qualities -- "whether it smells, looks, tastes the way customers have grown accustomed to." So a food that's past its use-by date may not taste quite the way the manufacturer intended, but it may be perfectly safe to eat.

"That's the whole critical thing," said Christine Bruhn, director of the Center for Consumer Research at the University of California, Davis. "With something like frozen biscuits, it's a best-by date. If you have it after that date, maybe your biscuits won't puff as much, but they'll still be safe to eat."

With other products, that may not apply. Bergman said that if the date on a meat item has arrived, it should be cooked and eaten, frozen or tossed.

"Meats have the greatest potential for danger," Bergman said. "Meat is a little different from other products" because of the potentially harmful pathogens it contains.

"Although those dates are really for quality purposes, they can be used as a guide" for meat, she said.

And "guide" is the key word. With most meat products, if they're a day or two past their dates, she said, they would still be considered safe. But more caution should be exercised in the case of ground meat. The grinding process involves an additional handling step, which means one more potential source of contamination. And since a batch of ground meat probably contains meat from more than one animal, that also increases the possibility of contamination.

Some foods, though, are completely safe for post-date use.

"When it's things like dried grains and beans, there's absolutely no danger in using those things past the pull date," Bergman said. "There's such a low moisture level that bacteria can't multiply on them."

In the case of condiments, "those are definitely quality dates," she said. Such foods are high in salt, and salt is a great preservative; "bacteria at a high level of salt just plain can't grow."

Companies mostly use the dates, it seems, more as a matter of self-protection than consumer protection.

"With mustard, you might get a little of a browning reaction," Bergman said. "It's not a safety issue, but consumers are going to look at it. The company doesn't want consumers seeing an off color, because they'll associate that with the product and perhaps not buy the product again."

And even the experts can disagree now and then. While Bergman said luncheon meats that contain nitrates can safely be held longer in the refrigerator, Bruhn said, "there are bacteria that can grow in refrigerator temperatures. It grows very, very slowly, but that can harm you." In the case of listeria, she said, as many as 28 percent of victims die.

"The food industry strives really hard to keep listeria from growing in your product," she said. But that type of bacteria is undetectable to the layman because it doesn't affect appearance or flavor, she noted.

"That's why manufacturers are trying to communicate with us and tell us to throw it out by the date."

Milk, she said, doesn't require a high level of caution because harmful bacteria is destroyed in the pasteurization process. Although, if you have visions of using spoiled milk in a cake recipe that calls for sour milk, think again (and use buttermilk instead).

"In the old days of our great-grandmother it would have tasted sour," Bruhn said. "But because all of those souring bacteria have been destroyed, it may have a bitter taste to it."

Dairy products usually can be used seven to 10 days beyond their package dates -- especially if you're careful to keep them refrigerated, and your refrigerator is 40 degrees or colder, she said. Trying to save energy by setting the refrigerator warmer just causes food to spoil more quickly.

"If you don't have a refrigerator thermometer, buy one," Bruhn said. "If you don't want to buy one, make it so cold that if it's any colder, your lettuce and your milk would freeze."

And Bruhn stressed that it's important to keep milk and luncheon meats in the coldest part of the refrigerator -- not on the door, which is warmest.

In the case of canned foods, she said, "there are some that have been eaten 50 years afterward." Expired canned foods will suffer only a deterioration in quality, she said. Exceptions are cans that have been dented or opened.

Foods that are kept too long in the freezer, she said, will suffer a loss in quality because of dessication.

"The surface will be dry and chalky and hard," she said. "You decide how bad is the quality. Do you want to eat it? Sometimes you can resurrect it in soup. But that is your own determination."

Then there are those products that may not have dates but have suffered a clear deterioration. Moldy fruits, she said, can contain toxic by-products, and the fruit's tissue spreads those toxins throughout the whole thing. So throw it out.

But many cheeses, she said, are made with mold, "and that mold is yummy." In the case of hard cheeses, she said, cut off the mold and a quarter of an inch of nonmoldy cheese and you can eat it.

Moldy bread, she said, just doesn't taste good. Then again, "if it's the last slice of bread and you've got to have a sandwich, you can cut that section off. It's not the type of mold that will be damaging to you, unless you're allergic to penicillin."

Bruhn noted that federal law does not mandate use-by dates except in the case of infant formula and some baby foods, and the dates on those items should be scrupulously observed.

Bergman said her rule of thumb is "If in doubt, throw it out."

In areas of the world with limited food supplies, she said, she'd advise cutting mold off of cheese or bread, because "one-time consumption is a quality issue.

"With our overabundance of food in the U.S.," however, "I think being safe is always the best way to go."

Contact reporter Heidi Knapp Rinella at hrinella@review journal.com or 702-383-0474.