Is your refrigerator running? If so, better go catch it.

That was a joke from the 1930s as kids crank-called on the phone. ("Do you have Prince Albert in a can? Better let him out," was another.)

It's not so funny if your electricity is off — and also your refrigerator.

Whether you faced that dilemma with the recent storms or want to be prepared for future ones this summer, keep these federal safety guidelines in mind:

It could take as little as four hours for some of the food in your refrigerator to go bad if the power goes off.

The temperature to keep in mind is 40 degrees. Anything perishable — such as raw meat, cooked foods or soft cheeses — that's been warmer than that for more than two hours should be discarded because bacteria grow in temperatures from 40 to 140 degrees.

"We want to be sure people don't needlessly put themselves at risk," said Craig Hedberg, a professor in the School of Public Health at the University of Minnesota. "The problem is that big storms in the summer are often accompanied by hot weather, and it puts more stress on the whole system."

Fresh produce generally can be saved, though prewashed packaged greens should be discarded, as should anything that's been in contact with raw meat juices. Do not gauge the safety of food by its taste or smell. Time and temperature are the guidelines to follow.

To help prolong the cold, keep your refrigerator closed. Don't dip in there for a glass of milk because each time you open the door you cause the refrigerator to warm up faster.

Frozen foods

Freezers, especially full ones, will stay cold longer than refrigerators, up to 24 hours for one that's half full, 48 hours for a full freezer. Dry ice or block ice can help maintain low temperatures in your freezer during extended periods. Fifty pounds of dry ice should keep an 18-cubic-foot freezer that's full of food cold for two days, according to federal recommendations. Frozen food also stays cold longer if it's bunched together rather than spread out on the shelf.

If frozen foods are thawed or partially thawed, they can be refrozen if there are still ice crystals in the food or if the food was at 40 degrees or below for less than two hours. The quality of the food may be affected by refreezing, but it should be safe to eat.

If food has become thawed or has been held at a temperature above 40 degrees for more than two hours, it should be discarded. If in doubt, throw it out, say those who deal with food safety.

For a list of safety guidelines for specific foods in the refrigerator or freezer, see

Follow Lee Svitak Dean on Twitter: @StribTaste.