I'm a food waste expert and here's how to freeze foods you didn't know you could - from crisps to hummus and even sandwiches - that'll save you so much time and money

At the time of writing, the contents of my freezer include a sad-looking, half-empty packet of peas; two jumpers (moths); a haphazardly filled ice-cube tray; and a loaf of sliced bread inside a plastic bag with an enormous rip down the middle.

Kate Hall’s freezer is rather more aspirational. 

The drawers are arranged by category – dairy, cupboard, bakery, fruit, vegetables, fish, meat, raw meat – and within those categories, individual groups of food are packaged separately in sealable plastic bags. (Hall likes the ones from Ikea, which cost £2 for 25 and can be reused.) 

These bags are then labelled and dated. In January, Hall went on BBC’s Morning Live. When presenter Gethin Jones saw a picture of her freezer he gasped and said, ‘It’s like a Filofax!’

Hall, 38, is a freezer expert based in Kent. Her Instagram account @thefullfreezer, where she shares freezer tips, has 68,000 followers. When Hall announced her debut guidebook, The Full Freezer Method, on social media, it went to number one on the Amazon home guides bestseller list thanks to pre-orders alone.

Hall got into freezing after having her second child. She was wasting ‘so much food’ – and money – and didn’t have time for batch cooking. But she did have time to, say, chop up a pepper and stick it in the freezer. Soon she started doing this with all the food that was about to go off in her fridge. ‘It was like finding a magical pause button,’ she says.

Kate Hall's ice trays are filled with things like leftover hummus or coffee. She even keeps eggs, which she has lightly beaten and then poured carefully into the trays

Intrigued, Hall wanted to find out just how much she could freeze – and in what ways. So she took a restaurant-level food hygiene course online to learn what was safe and unsafe, then got freezing.

The first trick, says Hall, is to make sure the food is flattened when you pack it into the plastic bags – that way it’ll defrost faster and you can fit more bags in your freezer.

Although, she warns, a freezer must never be too crammed: ‘You want it to be about 70 per cent full, so that it doesn’t have to work too hard.’ So, for example, a 70 to 100-litre freezer should be filled with about a carrier bag’s worth of shopping. 

Hall is also strict about how long cooked foods should cool before you freeze them: most dishes need about two hours while rice should have an hour. As for optimum freezer temperatures, Hall thinks about -18C. And, she says, although food can be kept in a freezer indefinitely, it is at its best eaten within three to six months.

Alongside her flat-packed bags, Hall keeps space to ‘open-freeze’ on trays. She chops up bananas or cooked chunks of chicken, ‘open-freezes’ them then decants the results into plastic bags.

Ice trays are filled with things like leftover hummus or coffee. Hall even keeps eggs, which she has lightly beaten and then poured carefully into the trays. There is about one egg in every two cubes. Apparently they freeze brilliantly. Who knew?

Whisked eggs and hummus aren’t the only strange things inside Hall’s freezer. She keeps peeled, parboiled potatoes which, once defrosted, she roasts (an excellent time-saver for Sunday lunch); lemons (she says frozen ones are easier to zest); filled sandwiches she has pre-made (perfect for packed lunches); nuts (for snacks); even crisps.

‘If you have a load of half-eaten packets of crisps left over from a party, just pour them into a plastic bag and stick it in the freezer,’ says Hall. 

You shouldn’t then decant all of the crisps into a bowl at room temperature – ‘they’re going to go stale really quickly’ – but they’re excellent if ‘you just want a handful on a Friday night with a gin and tonic’. 

Actually, says Hall, ‘Eating crisps straight from the freezer when they’re really cold, is, I think, nicer than eating them fresh. They are so crunchy.’ After our interview, I try a frozen crisp for myself. It’s odd at first, but then quite tasty. The only snag is that I very rarely just have a handful of crisps. But that is a me problem, not a freezer problem.

What can’t be frozen, then? Almost nothing, says Hall, although mayonnaise – and any sort of emulsion sauce – doesn’t freeze because it separates once defrosted. Other dairy products will split, too, as the fats separate from the water, but you can recombine them by ‘blitzing in a food processor, heating them, using them in cooking or, sometimes, giving them a really good shake’. 

Hall also warns against freezing any food you haven’t cooked yourself – for instance, takeaways – as you don’t know how many times it has been cooked or cooled. (You should only do either once.)

Hall estimates that she saves £1,000 a year by freezing food that otherwise would have been binned. It’s good for the environment, too; the UK wastes 9.5 million tonnes of food a year. A proportion of that will end up in a landfill, where it rots and releases methane.

Humans have been freezing food for a long time. In 1,000 BC, Chinese emperors commissioned subterranean ice cellars so they could store ice and food over the summer. 

There are still four ancient examples in Beijing’s Forbidden City; made from stone, they’re about two metres high, 11 metres long and more than six metres wide, with walls that are two metres thick. Hall would love them.

More recently, frozen food has gone gourmet. At Waitrose you can buy 200g of frozen miso butter for £3.50. The Times calls it a ‘wonder product’ and ‘umami bomb’. 

And UK brand The Truffle Company sells black winter truffles – the underground kind, not chocolate – which can be shaved from frozen. Yours for £39 per 50g.

Despite Hall’s Filofax freezer, she insists she’s not perfect. ‘I’m just a person that is trying. I’m trying really hard! I find people tend to have grown up in a household where it’s either: “We don’t waste anything.” Or, “Oh, is that OK? I’m not sure. I’ll bin it to be safe.” And I’m from the latter.’

Freeze it or fling it? 

Five foods you can freeze

EGGS Crack, whisk then freeze. Perfect for baking, omelettes or scrambled eggs.

CRISPS Frozen ones are crispier and tastier, says Hall.

FLOUR Weevil bugs can hide in flour – but freezing kills their eggs. Eek.

COOKED PASTA Just make sure it’s al dente, to avoid mushiness when defrosting.

CITRUS FRUITS Sliced, whole or peeled and segmented.

And five foods you can’t

HARD-BOILED EGGS The whites go rubbery. Yuck.

SALAD Freezing salad items separately? Tick. Freezing a ready-made salad? Expect sogginess.

JELLY It’ll become cloudy and mushy on defrosting (but freezing in lolly moulds and eating while frozen is fine).

EMULSION SAUCES Mayonnaise and hollandaise will separate on defrosting. 

TAKEAWAY LEFTOVERS High-risk, says Hall – you don’t know how many times it’s been heated before.

The Full Freezer Method by Kate Hall is published by Ebury, £14.99. To order a copy for £12.74 until 31 march, go to mailshop.co.uk/books or call 020 3176 2937. free uk delivery on orders over £25.