When the electricity goes out- how do you know if your food is safe to eat? The general guideline is to keep the freezer and refrigerator doors closed as much as possible to maintain cold temperatures for as long as possible. If unopened, the food will stay cold for up to 4 hours. A full freezer will hold the temperature for about 48 hours (about 24 hours if only half full) but only if the doors have remained shut. If in doubt, toss it.