A common worry is that food you’ve put in the freezer will sooner or later go off and make you sick.

If you keep the temperature of your freezer at minus-18 degrees Celsius or colder that won’t happen.

From a safety point of view, according to the Food Safety Information Council (FSIC), you can store frozen vegetables, meats and cooked foods such as soups and sauces, for years without any problem of food poisoning.

You can also safely re-freeze foods and meals that you’d already frozen and thawed.

But there are a few things to keep in mind. And we’ll get back to that.

The loss of quality

Store-bought frozen vegetables are high in nutrition when brought home, and – especially peas, corn and spinach – they maintain a fresh quality in taste and texture.

This is because they’ve been snap frozen in an industrial freezer.

The biggest problem, especially with your fridge at home – which takes longer to freeze foods than industrial machines – is that over time the food loses its nutrients and overall quality.

Texture and taste are the most obvious problems. So what’s the sweet spot to limit this loss of quality?

According to the FSIC, if you have a freezer/fridge combination you can store frozen foods “up to six weeks without any major quality effects”.

With a chest freezer, operating at minus-18 degrees, “the time is longer – three months or more depending on the fat content”.

The higher the fat content, the shorter the shelf life.

Recommended storage times can usually be found in the door or lid of your freezer.

Why re-freezing is tricky

Associate Professor Julian Cox is from the School of Chemical Engineering at UNSW. He is an associate professor in Food Microbiology. 

Associate Professor Julian Cox, giving food safety tips at Christmas. Photo: UNSW

The quality and safety of frozen foods is largely governed by the size of the crystal of ice that form from the water in the food as it’s freezing.

Cox told The New Daily that the faster you freeze food, the smaller the crystals. Industrial freezers tend to produce small ice crystals.

“When we put something in our domestic freezer, you’re getting formation of ice crystals that start to break down the natural structure of the food,” he said.

This is evident with fruit and vegetables that go a bit mushy after being frozen for a while.

(Prior to freezing vegetables at home, you should blanch them, then cool them quickly in iced water, so they don’t go brown when frozen.)

But it isn’t just food quality that suffers because of these ice crystals.

“What’s happened in that breakdown process is we’ve got nutrient cells breaking up and nutrients leaking out,” Cox said.

This “encourages bacterial growth” in the thawing process, he said.

The implications for food safety and spoilage, he said, “is once the food has been thawed, try and utilise it very quickly”.

Cox said that re-freezing “amplifies the effect” of nutrient leakage, bacterial growth and loss of quality.

“This is why people are against refreezing,” he said.

“Does it create a safety problem? Not really, because freezing it again is preserving the food. You’re stopping the opportunity for bugs to grow.”

The big turn-off is that those large ice crystals will develop, and the already degraded food loses more of overall quality.

Important point: Never thaw frozen food on your benchtop or in the sink at room temperature. You’re creating a petri dish. Always defrost in the fridge.

How to re-freeze most effectively

If you’ve thawed a leg of lamb or some other meats or fish, you’re better off cooking it, and then freezing it if needs be.

Refreezing vegetables and fruit, not so good for taste and texture.

Cox suggests a more winning scenario. Giving the example of thawing out minced beef, then cooking it with tomatoes and so forth as a bolognese sauce.

You’ve made too much. Now, when you’ve refrozen the minced beef, it’s in a cooked form.

“You’ve put another layer of preservative through cooking,” he said. “It will be less prone to break down down in the freezer than if you’d put the uncooked mince back in the freezer.”

Planning will deliver better results.

“If you make a big batch of bolognese, divide it up into small amounts so it will cool and freeze quicker,” he said.

“Once it comes out of the pot, steaming hot, put it in the fridge to cool. And then move it into the freezer. It’s a good idea to chill the meal before freezing.”

Cox also advises using good-quality freezer containers, and leaving as little headspace as possible. Air is not your friend.

A final word: Turn over the freezer’s contents as quickly as possible. Do you really need year-old steaks in the bottom of the freezer? Eat your food sooner rather than later. 

Read more here from the Food Safety Council about safe cold storage.