To help us save time in the kitchen, we need to know how to use our fridge and freezer effectively. However, many of us lack confidence when it comes to knowing whether a food is suitable to freeze, how to freeze food safely, and what actually happens to food when we freeze it.
Why do we freeze food?
Preservation is a type of food processing used to extend the shelf life of food, making it safe to eat for longer. Freezing is one of the oldest preservation methods around and is a quick and convenient way for us to preserve food at home.
Over time, exposure to air, moisture, heat, enzymes, and microbes (bacteria, yeast, and moulds) can affect the quality and safety of food, eventually leading to food spoilage. We can use preservation methods (such as freezing) to slow down the rate of spoilage, making our food last for longer.
Although microbes can cause food to spoil, it's completely normal to find microbes in our food. In some cases, it's actually necessary for flavour and texture (we wouldn’t have bread, cheese, or beer without them!). But the growth of unwanted microbes can make food unsafe for us to eat.
Generally, harmful microbes grow in warm and moist environments, where there’s food available to them. This is why keeping food in colder environments, like our fridge or freezer, helps to prevent these microbes from growing.
Freezing food can also help retain the quality and nutritional value, and saves time, as we can freeze batches of food to have at a later date.
What happens when we freeze food?
Seeing as microbes tend to grow in warmer conditions, reducing the temperature to around 5°C (fridge temperature) limits their growth. To completely stop microbial growth, we have to reduce the temperature to around -18°C (freezer temperature). It’s therefore important to check that our fridge and freezers are set to the right temperatures to keep our food safe.
When we freeze food, all the liquid turns solid, so there’s no moisture available for microbes to grow. When moisture is frozen it forms long, large ice crystals. Ice crystals take up more space than water, so they cause the cells in food to expand and break (similar to how a sponge expands when liquid is absorbed, the cells in food expand when liquid is frozen).
It’s because of this that foods with high water content (such as lettuce and cucumber) don’t freeze well. The freezing process damages the structure of these foods and reduces the quality.
While freezing stops microbes from growing, it doesn’t kill any microbes that were already there. This means that when we defrost or thaw food, the microbes become active again. Therefore, it’s important to follow any instructions on the packaging for how to freeze and reheat food safely.
Top tips for freezing food
As we’ve discussed, freezing food can be a very useful tool. So here are some of our top tips to help you freeze food well:
Blanch before freezing - this deactivates enzymes, kills bacteria, preserves colours, and retains nutrients. It works particularly well for vegetables and is how most packaged frozen vegetables are processed. To do this, plunge the vegetables into boiling water and then immediately into ice-cold water for a few seconds. Then, place the vegetables into a suitable container and freeze.
Freeze food in portions - this allows us to defrost one portion at a time, rather than the whole batch. Not only is this convenient, but it also helps to reduce food waste.
Use freezer bags - instead of using bulky boxes or bottles, save space in the freezer by using freezer bags
Label everything - write on each portion of food what it is and when it was frozen. This helps us to determine an approximate ‘use by’ date for the meals we freeze and keeps our freezer organised.
Freezer inventory - keeping a list of all the contents of our freezer means we won’t forget what’s in there!
Freeze before the food’s ‘use by’ date - this makes sure the food we freeze will be safe to eat when we later defrost it
To help make freezing as safe and easy as possible, we’ve created this table describing how to freeze different types of foods:
How to freeze
How long it can be kept in the freezer
Uncooked poultry and meat
Store in an airtight container or wrapped tightly in freezer bags
3-6 months. Before cooking, defrost in the fridge overnight.
Uncooked fish, raw, or cooked prawns
Store in a freezer bag. Freezing maintains the quality of white fish better than oily fish.
White fish: up to 6 months
Oily fish: up to 4 months
Prawns: Up to 6 months
Cooked meat and deli meats
Store in an airtight container or freezer bag. Meat may lose some moisture if frozen after cooking.
Store an airtight container or freezer bag
It’s best to grate the cheese before freezing it in a freezer bag. Soft cheese will have a watery texture once defrosted.
Fruit and vegetables
Freeze raw fruit and veg on a tray with baking paper (this stops them from forming one big clump). Once frozen, transfer to a freezer bag and store in the freezer.
Bananas - peel first and then place in a freezer bag (either sliced or left whole). These are great for smoothies!
Avocados - cut in half and peel, then either mash or leave whole. Add some lemon juice and put into a freezer bag. Defrosted avocados can be a bit mushy so they’re best to be used for sauces/dips.
Best within 2-3 months, but can be kept up to 6 months
Parboiled vegetables (e.g. potatoes, carrots, broccoli)
Parboil until just cooked, then place onto a baking tray and freeze. Once frozen, store in a freezer bag in the freezer. Some vegetables don’t freeze well when parboiled (see below).
Drain and press between two tea towels to remove excess water. Place in a freezer bag or airtight container.
Milk expands when frozen, so be sure to leave some extra space in the container/bottle to prevent it from bursting.
Whole milk doesn't freeze as well as semi-skimmed because of its higher fat content. Milk may also appear yellow when frozen, but this is ok!
Bread and baked goods
Slice bread before freezing and store in a freezer bag. Frozen bread can be popped straight into the toaster!
Crack each egg into a plastic muffin tray and place in the freezer. Once frozen, move into an airtight container. Defrost in the fridge overnight.
Garlic, ginger, and chilli
Garlic - bulbs can be frozen whole or chopped and stored in a freezer bag.
Ginger - wrap in cling film and place in an airtight container or freezer bag. Grate what’s needed for a recipe (straight from frozen), then place it back in the freezer.
Chilli - either slice or keep whole and place into a freezer bag to freeze.
Place portions in a freezer bag and freeze. Defrost at room temperature for a few hours.
Homemade meals (e.g. lasagne, pies)
Homemade meals can be frozen when raw, but note that the cooking time will be doubled if cooked from frozen raw.
Or, once cooked and cooled, place in a freezable dish and freeze.
Best within 3 months
Undercook by a few minutes (this will help the texture of the pasta once defrosted) and mix with a small amount of olive oil to prevent sticking. Place into an airtight container.
Grains and rice
Cook, cool, and store in an airtight container
Homemade soups, stews, curries, and chilli
Freeze once cooked. Defrost overnight in the fridge.
Place in a freezer bag or ice cube trays for small portions
Finely chop and place in a freezer bag.
Or, place ice cube trays and cover with water or oil before freezing. Once solid, transfer to a freezer bag. Frozen herbs are only suitable for cooking with once defrosted, not for garnish.
Some foods don’t freeze well, so we’ve summarised these below:
Why can’t it be frozen?
Any vegetable with a high water content (e.g. cucumber, lettuce, celery, radish, bean sprouts)
Having a high water content means they become soft, mushy, and limp when defrosted. But as they’re still safe to eat, they could be used in smoothies or soups!
Sour cream, yoghurt, mayonnaise
When defrosted, the water will separate from the fat, giving these an unpleasant taste and texture
These will become soft and soggy when defrosted
Top tips on food safety
Here are our top tips on how to freeze food safely:
Before freezing, allow any cooked food to cool down. Placing warm or hot foods into the freezer can raise the temperature of the freezer, creating an environment where microbes can grow. To help cool down food you might like to try:
Running food under cold water (such as rice and pasta), or placing it into a sealed container and running this under cold water
Portioning it out into smaller containers
Spreading food out in a shallow container
Placing food into a bowl and placing the bowl in an ice-water bath
Try to cool and freeze foods within 2 hours. Leaving cooked food at room temperature for much longer than this can increase the risk of microbial growth.
Use freezer suitable bags and containers - remember that liquid expands when frozen, so try to leave some space around foods and drinks to prevent spillage!
Store cooked and raw frozen foods in separate sections of the freezer to avoid cross-contamination
To thaw foods, place them in a refrigerator. Thaw foods away from other fresh foods to avoid bacteria spreading.
Once defrosted, cook within 24 hours to avoid microbes growing
Avoid refreezing food after defrosting as this can activate bacterial spores (forms of bacteria that can survive in adverse conditions and produce toxins)
When reheating a frozen cooked meal that contains meat, reheat until it’s piping hot (often it’s better to thaw these foods first). To make sure that food is piping hot, poke a knife into the centre and watch for steam to escape. If you have a food temperature probe, check the temperature has reached about 72°C in the thickest part.
There are lots of misconceptions about freezing food, which can make it more difficult to know whether we’re doing things safely and effectively. So, for the final part of this guide, we’re going to bust some freezing myths.
Myth: Frozen food has fewer nutrients than fresh
Freezing helps to retain the nutrient content of most foods. This is particularly true for fruits and vegetables, as they’re picked when ripe and frozen straight away. However, some vitamins (like vitamin C) are heat sensitive, so the blanching part of the freezing process can destroy them.
Myth: Frozen food doesn’t have a ‘use by’ date
Frozen food can be stored indefinitely without necessarily ‘going off’ because microbes can’t grow and cause spoilage in these conditions. However, the quality can reduce over longer periods of time and cause food to become unappetising to eat once thawed.
How long food can be kept in the freezer will vary between food products (see the table above). As a general rule, most frozen foods last well for about 3 months and no food should be kept for longer than 12 months in the freezer.
Myth: All food can be refrozen
We can refreeze food but only if the defrosted food was raw, then cooked, and then refrozen (we shouldn’t refreeze raw food). This is because microbes grow faster on food that has been frozen and thawed, but cooking will kill any harmful ones. It’s also worth noting that refreezing in this way may reduce the quality of the food.
Myth: Alcohol doesn’t freeze
Alcohol can freeze, but often it requires lower temperatures than that of our home freezers (-18°C). Beer and wine can be frozen at this temperature because of their higher water content. Our top tip for freezing leftover wine is to freeze it in an ice cube tray. One cube can be enough to add flavour to a meal at a later date (frozen wine cubes will last around 3 months).
Overall, freezing food has many benefits including increasing shelf life, retaining the quality and nutritional value, and reducing food waste. Freezing allows us to batch cook food in advance so we have convenient, healthy, homemade meals ready for whenever we need them.
Take home messages
Freezing is a quick and convenient way for us to preserve food at home
Over time, exposure to air, moisture, heat, enzymes, and microbes (bacteria, yeast, and moulds) can affect the quality and safety of food, eventually leading to food spoilage. Freezing slows down the rate of spoilage, making our food last for longer.
Microbes tend to grow in warmer conditions, so reducing the temperature to around 5°C (fridge temperature) limits their growth. To completely stop microbial growth, we have to reduce to temperature to around -18°C (freezer temperature).
When we freeze food, all the liquid turns into ice crystals, so there’s no moisture available for microbes to grow
Some of our top tips for freezing food include blanching before freezing, using freezer bags, labelling everything, and keeping a freezer inventory
Different types of food can be kept in the freezer for different lengths of time - we’ve summarised this in the table above
It’s important to be aware of how to freeze food safely, take a look at our top tips for this above!
Freezing food has many benefits including increasing shelf life, retaining the quality and nutritional value, and reducing food waste
Written by Reema Patel, Nina Evans, and Simi Ryatt - Health Coaches at Second Nature