When a strong thunderstorm barreled through the area earlier this month, it left many homeowners without power for a good number of hours, some for as long as 18 hours.

As each hour ticked by, no doubt many were concerned about the food in their refrigerators and freezers. How long would it stay safe to eat?

Some may have gone in search of ice and coolers right away to transfer items. Others may have opted to wait it out.

Depending on when the power returned, that's a gamble if the food would still be edible, said Mary Schroepfer, nutrition and health education specialist at the University of Missouri Extension office in Union.

"The rule is that a full fridge, without power, will keep food safe for four hours - but that's if there's no peeking or reaching in to grab something," said Schroepfer. "Once four hours is past, you should throw things out."

Not everything has to go, though, she noted. There are many items people keep in the fridge that wouldn't be spoiled - the United States Department of Agriculture's Food Safety and Inspection Service has a list on its Web site (www.fsis.usda.gov) of what can be saved and what should be tossed.

The safe list includes hard cheeses like Cheddar and processed cheeses, butter and margarine, fruit juices that have been opened, fresh whole fruits, fresh raw vegetables, vinegar-based dressings, breads and tortil-las, to name a few.

The unsafe list, however, is much longer - all meat, poultry and seafood whether they are raw or cooked leftovers, gravy, stuffing, pizza with any topping, soft cheeses like cottage, cream and mozzarella, shredded cheeses, dairy products including sour cream and yogurts, eggs including fresh, hard-cooked and any egg products, cooked pasta, any fresh fruits that have been cut, cream-based dressings, spaghetti sauce, greens that have been precut, prewashed or packaged, cooked vegetables . . . and the list goes on.

The reason these foods become unsafe to eat is bacteria, said Schroepfer.

When foods are in the refrigerator, bacteria growth is minimized, she said, but as soon as those foods begin to warm up, the bacteria begins to grow and at a faster rate. Some of the food items on the toss list may surprise people - like, why are fresh fruits safe but cut fresh fruits not?

"It's because there could have been bacteria on the knife," explained Schroepfer.

Why do you have to toss opened spaghetti sauce? "It's like a cooked vegetable," she said.

Cooked pasta goes bad because of the moisture content, Schroepfer noted.

"The moister the product, the more problematic it is," she said. "And the longer it is exposed to room temperature, even during the cooking process, the greater problems there can be."

What About the Freezer?

Foods in the freezer can stay put much longer before they start to go bad. If the door remains closed, a full freezer will keep foods frozen for about two days, said Schroepfer.

However, there are some factors that can affect that, including the amount and types of food in the freezer and the size of the freezer.

"A full freezer is always better," said Schroepfer. "The food will always stay colder longer than in a half-filled freezer."

Meats in the freezer will take longer to begin thawing than baked goods, and a larger freezer will keep foods frozen longer than a small one.

If frozen foods have begun to thaw, most can be refrozen without worry in two cases - if the food still contains ice crystals or if it had been at refrigerator temperature (40 degrees) for less than two days.

Still, there are some important things to note, said Schroepfer.

Refrozen meat should be used in casseroles or similar dishes to mask any flavor and texture changes. Seafoods, even if they still contain ice crystals, should never be refrozen. Cook them immediately. Also, ice cream that has been refrozen may not only taste funny, it may be unsafe - again, throw it out.

"I always say, ‘If in doubt, throw it out,' " said Schroepfer. "A trip to the doctor will cost you more in the long run than the cost of what you're throwing out."

Getting sick, even death, is a definite risk when eating any foods that have been at room temperature for too long.

"If you're someone whose health is fragile, you can die from food poisoning," said Schroepfer.

She cautions people all the time about large gatherings - like Thanksgiving or Easter - where food may be served and then left out while the family eats and even afterward as they sit around the table talking.

"Bacteria is growing that whole time," she said. "I tell people, ‘When you serve meals, don't linger and talk - put it in the fridge.'

"No perishable food should be kept at room temperature for more than two hours."

Tips to Keep Food Safe

Schroepfer said there are some things people can do ahead of time to keep their foods safer longer.

For starters, if they know a severe storm is expected and think there is a chance the power would go out, lower the freezer temperature from its usual 0 degrees to -10 or -20.

"It will take longer for foods at that temperature to thaw," she noted, and it doesn't do any damage to the food if the power never goes out.

Likewise, you can set your refrigerator temperature a bit lower. Also, some foods from the refrigerator may be able to be put in the freezer to keep longer in the event of a power outage.

People who opt to get ice to keep their foods safe should know that block ice is better than cubed, but dry ice is best.

"But you have to be careful when you're handling dry ice," Schroepfer warned. "It can be dangerous to work with.

"You need to wear gloves because it can't touch your skin, and you can't let it touch the food either. You should set the dry ice on a cardboard box or something on top of the foods."

One other thing Schroepfer tells people to think of ahead of time - if the power does go out suddenly, where could you go to buy ice quickly?

It's always best to be prepared and have a plan, she said.

A complete list of which foods should be tossed after being at room temperature for more than two hours can be found on the Food Safety and Inspection Service Web site, www.fsis.usda.gov in a fact sheet titled, "A Consumer's Guide to Food Safety: Severe Storms and Hurricanes."

The University of Missouri Extension also has more information on its Web site, www.extension.missouri.edu, in a document titled, "Quality for Keeps: Freezer Problem Solver."