How do freezers work, and do they kill bacteria?

How do freezers work, and do they kill bacteria?
(Image credit: Getty Images)

Most people have a freezer within their home that they use every day, whether that’s for storing leftovers or stashing ice cream. And while the best freezers are a god-send for keeping quick meal ingredients in, how much do you understand about how they actually work? Or more importantly, how good are they at killing off any harmful bacteria through the freezing process?

These essential household appliances extend the life of many foodstuffs, thanks to their power of stopping the growth of bacteria. That means you can thaw a food you froze a month ago and enjoy it without the time constraints that fresh produce has. In order to enjoy these benefits, it’s better to freeze food sooner rather than later to avoid it being in bad shape, such as with mushy or molding foods. 

When it comes to bacteria, it’s good to do what you can to avoid having nasty microbes on your food in the first place, which comes with regular hand washing and cleanliness practices, but can also be assisted by blanching certain foods, such as vegetables, before freezing. Blanching, the process of partially cooking food in boiling water, will kill any lingering microbes, meaning that your food will go into (and emerge from) the freezing process in a better condition.

It’s also important to store your frozen foods with maximum efficiency in order to achieve freshness. For example, using freeze-friendly bags to repackage your food will prevent unnecessary space from being taken up by various boxes floating around. For more tips on how to perfect the inside of your appliance, check out our feature on which freezer is best for food storage

An image of frozen blueberries, broccoli and berries in separate bags

(Image credit: Getty)

How do freezers work?

According to How it Works, the first thing to know is that these appliances usually keep to a temperature of around minus 22 degrees Celsius. That’s pretty chilly compared to the average temperature of a room, around 20 degrees celsius. Some have a thermometer, so you can check for yourself.

Getting down to the mechanics of how do freezers actually work, the hard graft is all going on within your appliance’s compressor. There are two coils at work, the condenser coil, and the evaporative coil, separated by an expansion valve. Within the first coil, the condenser, there’ll be a gas that has a boiling point near to 0 degrees celsius. 

The freezer works to compress this gas, which means that it heats up. As it heats, the hot vapor is sent through the expansion valve into that second evaporation coil we mentioned previously. The pressure in the second coil is much lower than the first, hence its name, meaning that the gas evaporates, a liquid coolant is created and cooling occurs throughout the rest of your appliance.

After turning into a gas, the process begins all over again, with the condenser coil stepping in to turn it back into a liquid. This endothermic process (the action of absorbing heat) involves pressurization, which completes the cycle and generates the coldness. However, this heat must be directed away from the freezer itself, or risk melting all your precious ice cream, which is why you’ll find most appliances have fans in order to dissipate that warmth. 

What affects the ability to freeze properly?

With all that going on within, you might be wondering if there’s anything you can do to prevent the cooling process from going wrong. Preventing heat from being circulated to the wrong part of your appliance is key, which is why obstructions to your fan system may spell trouble. 

Practically, it also means you should take more care when it comes to closing the doors, and prevent any heat from getting in. This is the case whether you own a French door refrigerator or one of the best side by side refrigerators. By keeping warm air out, your compressor won’t have to work so hard, so you’ll save energy and keep your foods fresher.

How do freezers work, and do they kill bacteria: A picture of three tubs of ice cream sat next to one one, one chocolate, one vanilla, one strawberry

(Image credit: Getty Images)

In order to do this, you might also want to take a check on the appliance's door seals, and make sure that they are working as efficiently as they can be. You also want to make sure your freezer isn’t so jammed full that cold air can’t circulate. Though it might seem like an excellent idea when you’re able to fit everything in, overstuffing can actually act as a huge detriment to the freezing system. 

Do freezers kill bacteria?

You might be wondering what kind of effect the intense coldness within your appliance has and whether freezing is a viable solution for killing off harmful bacteria.

At -22 degrees, the average temperature of a household freezer is cold enough to freeze any microbes, bacteria, yeast, and molds present in foods, according to the US Department of Agriculture (USDA). However, the important distinction to be made here is that your freezer cannot kill the harmful bacteria within foods, only freeze them. 

That means that once your food has defrosted, those pesky harmful microbes will once again become active. Anything that was initially harmful within those foods still remains within it after thawing, so you still need to be vigilant with the things you’re consuming once frozen and once defrosted.

This information is important not only because it means that you still have to be careful with the preparation and cooking of any frozen foods, but because thawed foods should also be treated as if they were fresh, and eaten within a short period of time so that bacteria cannot multiply. The recommended time period for eating any food after thawing is 24 hours. For more on how you can save time and money, check out our feature on how long leftovers last.  

How do freezers work, and do they kill bacteria: a wooden bowl of frozen carrots, cauliflower and broccoli

(Image credit: Getty Images)

A guide to how long certain foods last in the freezer

  • Bacon - one month 
  • Sausages - two months
  • Mince - four months 
  • Whole chicken - one year 
  • Chicken breasts/piece - six to nine months 
  • Cheese - three months 
  • Berries - three months 
  • Cooked meals - three months 
  • Blanched vegetables - one year  
  • Bread - one year  

What are the benefits of freezing food?

Anyone who owns a freezer is aware of their practical benefits. Whether it’s freezing food that’s soon to go out of date for midweek dinners, or keeping a food item that you use less regularly and don’t want to repurchase fresh, they can save you both time and money.

But there are also benefits within the process of freezing itself, and these are to do with getting the most nutrition from frozen fruit and vegetables. According to experts at Harvard Medical School, the freezing process can boost the nutritional value of fresh produce. As such, no additional preservatives will need to be added to your food. If anything, Vitamin C that is often added to food in order to keep it from browning also boosts the vitamin levels within your diet, which makes for good news all around.

So, frozen fruit and vegetables shouldn’t be overlooked as less healthy, and are an often cheaper and quicker way to insert one of your five a day into mealtimes. With a balance of healthy meals and sweet treats such as icecreams, it’s easy to see why these appliances are one of the most valuable home appliances around. 

Molly Cleary

Molly is the Staff Writer for the Home Section at Top Ten Reviews, joining the team after finishing college. When she's not writing she enjoys baking and embroidery, as well as getting stuck into a good book. She now enjoys writing about kitchen appliances, gardening tools, and will even dip her toe into writing about fridges and ovens.