How to Freeze Leftovers Safely, Plus How to Thaw Them

Freezing is one of the easiest ways to make the most of a big cook-up and waste less food. But how you cool, portion, thaw and reheat food all matter. This guide covers the official Australian advice, step by step, so you can freeze leftovers with confidence.

Why freezing works, and what it doesn't do

Food Standards Australia New Zealand (FSANZ) explains that most food poisoning bacteria grow quickly between 5°C and 60°C, the "temperature danger zone" (FSANZ, Microorganisms and foodborne illness). Freezing keeps food well below that range, and the Food Safety Information Council (FSIC) notes that at freezing temperatures many food poisoning bacteria either don't grow or grow much more slowly (FSIC, Fridge and freezer food safety). Freezing doesn't kill them, though. Whatever was on the food before it went in is still there when it thaws. That's why the steps before freezing and after thawing are just as important as the freezer itself.

Step 1: Cool leftovers quickly

The most important thing when freezing cooked food or leftovers is to cool it quickly. FSIC advises cooling food on the bench only until it stops steaming, then putting the hot food straight into a container, covering it with a lid and putting it in the freezer (FSIC, Fridge and freezer food safety).

Don't leave a pot of soup or curry on the stove overnight to cool. FSIC warns that if large amounts of food cool too slowly, toxins can form that can make you very ill (FSIC, Food storage: pantry, fridge or freezer).

Step 2: Portion into smaller containers

FSIC recommends avoiding freezing large amounts at once, because a big block takes longer to freeze and bacteria could multiply. Split food into smaller quantities in separate containers instead (FSIC). FSIC suggests containers about the size of a takeaway container (FSIC). Smaller portions also mean you only thaw what you need.

As a rough guide to sizes in our glass vacuum container set:

• 470ml: a single serve of soup, sauce or stewed fruit.
• 800ml: one generous lunch or two smaller serves.
• 1.4L: a family dinner portion of bolognese or curry.
• 2.7L: bulk batches, or bigger items like a lasagne.

Step 3: Freeze within the safe window

Leftovers don't have to go into the freezer the day they're cooked, but don't wait too long. FSIC says refrigerated cooked dishes or leftovers should be used or frozen within 2 to 3 days, or within 24 hours if you are pregnant, elderly or have a weakened immune system, because of the risk of Listeria (FSIC). Freezing doesn't reset that clock. Our guide on how long leftovers last in the fridge has more detail.

Step 4: Label, date and check your freezer

FSIC suggests labelling and dating food before it goes in the freezer (FSIC). A date dial on the lid, or a strip of masking tape and a marker, makes it easy to see what's there and use the oldest food first.

Frozen food should be kept at -18°C or below, which is the normal operating temperature of a domestic freezer. At this temperature food should be frozen solid. If you can't easily check your freezer's temperature, make sure food looks and feels frozen, or use a thermometer that covers that range. FSIC notes that partially frozen food will have a shorter shelf life, and that defrosting your freezer regularly to limit ice build-up helps it run efficiently (FSIC).

A note on freezing in glass

Borosilicate glass generally copes with temperature changes better than ordinary soda-lime glass, but no glass container is unbreakable. Liquids expand as they freeze, so it's sensible to leave some space at the top of the container rather than filling it to the brim. It's also wise to avoid sudden, extreme temperature changes, such as moving a container straight from the freezer into a hot oven or pouring boiling liquid into frozen glass. Always follow the care instructions that come with your containers, and take lids off before the oven or microwave.

Removing air with a pump can help limit air contact with food, but it doesn't make frozen food safe for longer. For more on what vacuum sealing can and can't do, read our guide to vacuum sealing food at home.

How to thaw leftovers safely

This is where many people slip up. FSIC advises thawing cooked or ready-to-eat foods in the fridge or the microwave, not on the bench (FSIC). On the bench, the outside of the food can sit in the danger zone while the middle is still frozen.

• In the fridge: the safest option. Move tomorrow's dinner from the freezer to the fridge the night before. Larger portions take longer, so plan ahead.
• In the microwave: use the defrost setting when you need food sooner, then reheat or cook it straight away.
• Raw meat and poultry: FSIC says poultry and rolled, stuffed or boned meat joints must be thawed right through to the centre before cooking, as they could otherwise stay undercooked in the middle (FSIC).
• Packaged frozen food: follow the instructions on the pack, as some foods don't need thawing before cooking.

Can you refreeze food?

Yes, in some cases. FSIC says that if you've defrosted too much raw meat or poultry, it's OK to refreeze it, although it may lose some quality because freezing breaks down the cells and the food becomes a little watery (FSIC). As a general rule, only refreeze food that was thawed safely in the fridge. Food that has been thawed on the bench, or left in the danger zone, shouldn't go back in the freezer.

Reheat to 75°C

When it's time to eat, reheat leftovers until they're steaming hot all the way through. FSIC recommends reheating to 75°C, using a food thermometer or your microwave's reheat function and following any prompts, such as stirring the food (FSIC).

Make freezing part of your routine

Freezing works best when it's planned. Cooking once and freezing portions for later is the backbone of good batch cooking. If you're new to it, our meal prep for beginners guide walks through a week of lunches. Our glass vacuum container set includes four sizes with date-dial lids to help you track what's in the freezer, plus a rechargeable vacuum pump. If you need a spare, there's a replacement rechargeable pump and a no-charging manual pump.

Sources: Food Safety Information Council, Fridge and freezer food safety and Food storage: pantry, fridge or freezer; Food Standards Australia New Zealand, Microorganisms and foodborne illness. This guide is general information only.