A full freezer stays cold for about 48 hours if you keep the door closed. A half-full freezer? Maybe 24 hours. The difference is thermal mass — more frozen stuff means more cold stored in the food itself, which keeps everything colder longer.

I found this out the hard way during a summer storm that knocked out power for 36 hours. My half-empty freezer was a puddle of melted ice cream and questionable chicken by the time the lights came back on. My neighbor’s packed freezer? Everything was still solid.

Now I prep before storm season. Here’s what actually works.

Freeze jugs of water to fill empty space

Clean milk jugs or plastic bottles filled with water and frozen. They serve as ice blocks that keep the temperature stable and give you emergency drinking water when they melt. Fill them about three-quarters full — water expands when frozen.

Even when the freezer is full of food, I keep a couple of frozen gallon jugs on the bottom shelf. They act as a cold battery and reduce the workload on your freezer compressor, which slightly lowers your electricity bill too.

Know the one-cup trick

Freeze a cup of water, then place a quarter on top of the ice. Keep this cup in your freezer at all times. If you come back after an outage and the quarter is at the bottom of the cup, the ice melted completely and refroze — meaning your food warmed up enough to be unsafe. If the quarter is still on top or only slightly sunken, the temperature stayed cold enough.

This is the trick my grandmother used. No thermometer, no guessing. Just a quarter on ice.

Group food together

Before storm season, group similar items together in the freezer so they stay colder as a solid block. Meat on one side, vegetables on another, prepared meals together. The denser the grouping, the longer everything stays frozen.

For the fridge: keep a few frozen gel packs or frozen water bottles in the freezer. If the power goes out, move some to the fridge to buy extra time for milk, eggs, and other perishables. A fridge without power stays safe for about 4 hours. Adding ice packs can stretch that to 8-12 hours.

What to toss and what to keep

After an extended outage: throw out anything above 40 degrees for more than two hours. Meat, dairy, eggs, cooked leftovers — all of it. Condiments, hard cheeses, and raw vegetables can typically survive warmer temps. When in doubt: if it smells off or feels slimy, toss it. Food poisoning is more expensive than a new carton of milk.

I keep a thermometer in both the fridge and freezer now. They cost about eight dollars each and remove the guesswork entirely.