The overall Which? test score is made up of the following star ratings, all determined by our rigorous lab tests.
How we test freezing power
How quickly it can freeze, or how much it can freeze in one go. The greater the freezer power the faster it will freeze your food, minimising the chance for bacteria to grow and helping ensure food is as fresh and nutrient-rich as possible when you defrost it.
How we test ease of cleaning
How easy it is to remove parts for cleaning. This test was introduced when we changed our freezer test programme in January 2015 - models tested before this date don't have a star rating for ease of cleaning.
How we test energy efficiency
How energy-efficient the freezer is for the amount of usable space it offers. Freezers are switched on 24/7, so it's important to choose one that won't cost a fortune to run. The best freezers score four or five stars and use a minimal amount of energy to cool food. You can spot the real energy guzzlers as they're awarded a poor one or two stars in this test.
How we test thermostat setting
To see whether you can rely on a freezer's thermostat to create perfect temperatures for storing frozen food, we set the freezer up following the manufacturer's recommended thermostat setting. Models scoring five stars have reliable thermostats that are spot on, whereas for models scoring two stars or less you would need to set the temperature using a thermometer.
How we test temperature stability in hot conditions
We test how closely the freezer maintains the correct temperature when the room temperature rises, just as it does in your kitchen at home. We do this by turning the room temperature up to 35°C and testing the temperature of the food-equivalent gel packs inside the freezer. Five stars means the gel packs stay perfectly frozen, which is what you want for your food. But two stars or less means the gel packs either warm up or over-freeze.
How we test quietness
We assess how noisy each freezer is when the compressor's running and when it switches on and off.
How we test insulation
A well-insulated freezer will keep your food safely frozen for hours during a power cut, but some freezers cause food to quickly thaw. So in our test lab, we turn the power off and time how long it takes our food-equivalent gel packs to rise from -18°C to -9°C. Models scoring four or five stars are well-insulated and capable of slowing the thawing process, whereas the temperature of food stored inside models that score one or two stars will quickly rise.
How we test ease of use
To see whether a freezer is easy to use, we rate aspects such as how sturdy the drawers are, how smoothly the drawers slide in and out and whether they're easy to remove completely, whether the freezer is easy to programme and whether the thermostat is easy to adjust.
