Four hours is the window extension services give a closed refrigerator during a power outage, and 24 or 48 hours is the window for a half-full or full freezer. Once the power is back, five checks help sort what is still usable, from a small container of ice kept in the freezer to a food thermometer slipped between frozen packages. The guidance here comes from Illinois, Wisconsin and North Carolina extension services, which agree on most numbers and differ by a degree on one.
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1. A Cup of Ice Kept in the Freezer
Illinois Extension relays a tip from University of Nebraska Extension for homes where the outage length is unknown: store an ice cube or two in a sealed plastic bag or small container in the freezer. If the ice has melted down from its original shape, the power was off for an extended period, and one that has melted completely means the outage lasted long enough that discarding all the food is the safest option.
The reason for the tip is that food in a refrigerator or freezer can reach an unsafe temperature during an outage and cool again once power returns, which makes it look fine. Craftingyourhome.com has a post titled 8 Things Never to Do Before Leaving Home for Thanksgiving Travel.
A popular version puts a coin on top of the frozen cup. In a June 4, 2025 column, N.C. Cooperative Extension’s Cheryle Syracuse reported that two extension food safety specialists, Ben Chapman of NC State and Don Schaffner of Rutgers, judged the coin method unreliable. Ice is less dense than water, so a coin on top stays on top, and the cup could melt substantially and refreeze with the coin still sitting on the ice. The specialists suggested temperature loggers instead, with gel strips and dots as a cheaper option.
Syracuse’s other column describes a bottle variant: freeze a partly filled bottle of water on its side, then stand it upright. If the water is still frozen when the bottle is checked, that is a good indicator the freezer did not thaw. If it has melted, she writes, the food should be assumed to have thawed too, and the rule is when in doubt, throw it out.
2. The Clock: 4 Hours and 2 Hours
Illinois Extension says refrigerated food is safe for up to 4 hours during an outage if the door stays shut as much as possible, and that after 4 hours perishable foods such as raw meat, poultry, fish, dairy, eggs and leftovers should be thrown out. A half-full freezer holds safe temperatures for up to 24 hours and a full one for up to 48 hours, according to the same page.
The Wisconsin extension page adds a second clock. Any perishable food that was above 40°F for 2 hours or more, or 1 hour if temperatures were above 90°F, should be discarded. North Carolina’s Syracuse suggests writing down the time the power went off so there is a reference point, and says she would not wait for the 4 hours to run out before checking the refrigerator. Craftingyourhome.com has a post titled Before the First Widespread Freeze Hits the Southeast This Weekend: 6 Ways to Protect Potted and Garden Plants.
Syracuse says that if an evacuation keeps the food from being monitored and the power was off for more than 4 hours, the refrigerator food should be assumed to have been above 41°F and thrown out. Frenz Hub has a post titled Best Practices for Seasonal Storage.
3. Ice Crystals on Frozen Packages
Illinois Extension says foods with ice crystals, or at 40°F or colder, can be refrozen, though quality may decrease. Wisconsin’s page gives the same test and adds that appearance and odor cannot be relied on. Food that still contains ice crystals or is 40°F or below is safe to refreeze or cook, it says. A North Carolina extension agent likewise wrote that food is safe to refreeze if it still has ice crystals or the freezer did not rise above 40°F.
Syracuse notes that food in the front, on the door or in small, thin packages defrosts faster than large, thick items or food at the back or bottom. That means one packed shelf may pass the ice-crystal check while another does not. Frenz Hub has a post titled How to Freeze Fresh Green Beans to Enjoy All Year.
4. Appliance Thermometers in Both Compartments
Illinois Extension recommends separate refrigerator and freezer thermometers and gives the targets: freezer at or below 0°F and refrigerator at or below 40°F. Once power returns, it says, the readings should be checked. If the refrigerator thermometer reads above 40°F and the power was out 4 hours or more, all perishable foods should be thrown out.
Wisconsin gives the freezer counterpart: if a thermometer was kept in the freezer and reads 40°F or below when power returns, the food is safe and may be refrozen. North Carolina’s Syracuse uses 41°F as the line for the refrigerator, so the numbers differ by a degree between the two states’ guidance. Frenz Hub has a post titled 2026‘s Most Clever Storage Hacks to Maximize Every Inch of Space.
5. A Food Thermometer Between Packages
Without a freezer thermometer, Illinois Extension says to feel for ice crystals on freezer packages or place a regular food thermometer between packages to see whether foods are 40°F or colder. In those cases the food is safe to refreeze. Perishable foods such as milk, juice and meat that were above 40°F for 2 hours or more should be thrown out.
Syracuse suggests keeping a food thermometer on hand for the first check after an outage: the temperature of food items, milk or other liquids. If power is out for a while, she says, ice packs in the refrigerator or foods packed into coolers with ice can help keep food below 41°F.
What Extension Services Say Not to Do
Illinois Extension says not to put perishable food outside during a winter outage. Outside air may not be cold enough, it notes, and as the sun moves a previously shaded spot can warm up, while snow can expose food to dirt and animals. Wisconsin gives a similar warning about fluctuating temperatures and small animals.
Wisconsin also advises cooking meat, poultry, fish or eggs that are still at safe temperatures to a safe minimum internal temperature, and Illinois suggests cooking in small batches during an extended outage because leftovers cannot be saved unless power returns soon.
This article was produced with AI assistance and edited for accuracy against the sources linked above.
