Freezers should be set at 0 degrees Fahrenheit according to the U.S. Food and Drug Administration. While this is the temperature necessary to keep food safe in long-term storage, food quality is often extended if freezer temperatures are reduced to -10 or -20 degrees Fahrenheit.
Freezing food doesn't change its nutritional content, although improperly packaged food may experience freezer burn that affects the quality and taste of the cooked item. A full freezer maintains a safe temperature for up to 48 hours in the case of a power outage. If the freezer temperature stays below 40 degrees Fahrenheit, it's safe to refreeze the food.