How do I get frozen food home without it thawing?

In winter this looks after itself. In summer the car is the problem: a parked car interior reaches temperatures far above the outdoor air within minutes, and the boot is often the hottest part of it. The whole task is minimising the number of minutes the food spends warm, and giving it enough thermal mass to survive the ones it cannot avoid.

Safety

Step by step

1. Do the frozen aisle last, always.Every minute frozen food spends in a trolley at supermarket temperature is a minute of its budget gone. Chilled goods second to last, frozen goods absolutely last, then straight to the checkout. This single change usually matters more than any bag.
2. Take an insulated bag every time in summer.Supermarket insulated bags are inexpensive and effective. Keep them in the car so you are never without one — the trip where you forgot is the one where the ice cream is soup. A frozen ice pack kept in the freezer and thrown in on the way out doubles the effect.
3. Pack frozen items tightly together.A dense block of frozen food acts as its own cold reservoir and thaws from the outside in, which is far slower than individual packets warming separately. Put everything frozen into one bag, packed tight with no air gaps, rather than distributing it across several bags.
4. Keep frozen and chilled separate from everything warm.Hot roast chicken, fresh bread and anything just out of an in-store oven should be nowhere near the frozen bag. Bags of cleaning products and tins are useful as an outer buffer around the cold bag.
5. Put it in the cabin, not the boot.A boot is unventilated, often dark-lined and frequently the hottest part of a parked car. The footwell behind a front seat, in the shade, with air conditioning running, is considerably cooler. If the car has been standing in the sun, run the air conditioning and open the windows for a minute before loading.
6. Go straight home.The second errand is where frozen shopping is lost. If you must stop, do it before the supermarket rather than after, and never leave shopping in a parked car in summer while you do something else.
7. Unload the freezer items first.Frozen goods into the freezer before anything else is put away, chilled goods next, then everything else. The two minutes spent putting away tins first is two minutes off the frozen food's budget.
8. Assess anything that has softened.Still hard with ice crystals present and still properly cold means it can go back in the freezer, though texture may suffer — ice cream in particular is never the same. Fully soft, warm to the touch, or with juices pooling in the packaging means it must not be refrozen: cook it thoroughly immediately, or discard it.
9. Give the freezer a chance to recover.A large load of partly softened food put into a domestic freezer at once raises the temperature of everything around it. Spread it out rather than stacking it in one place, avoid opening the freezer for a while afterwards, and use the fast-freeze setting if the appliance has one.

Tips

• Keep a couple of ice packs in the freezer permanently and take one whenever you shop in summer. They cost very little and they change the arithmetic completely.
• Online delivery is genuinely the better option in a heatwave for a big frozen shop, because it arrives in a refrigerated van rather than sitting in your car.
• If you regularly shop far from home, a hard cool box in the car boot with a frozen block in it turns a long drive into a non-issue.
• Bags of frozen peas or ice packed around more delicate frozen items work well as extra cold mass on a long journey.
• Ice cream is the most vulnerable item in the trolley and the best indicator. If the ice cream is still hard when you get home, everything else is fine.

Common mistakes

• Shopping the frozen aisle first out of habit — It can add half an hour to how long the food spends warm before it is even paid for, which is often the largest single part of the total.
• Putting shopping in the boot on a hot day — An unventilated boot is frequently the hottest part of a parked car, well above outdoor air temperature. The shaded footwell in the cooled cabin is far better.
• Spreading frozen items across several bags — Separated packets each warm on their own. Packed tightly together they behave as one mass and stay frozen much longer.
• Refreezing food that has fully thawed and warmed — Freezing halts bacterial growth but does not reverse it. Anything that has been properly thawed and warm should be cooked immediately or thrown away.

Questions people ask