Flash freeze

Flash freezing means spreading food out in a single layer on a tray and freezing it uncovered until each piece is solid, then packing it into bags. Because the pieces freeze apart, they do not stick together, and you can take out exactly as many as you need. In the UK it is often called open freezing. In factories, very cold air does the same job much faster.

How to do it

1. Line a sheet pan (baking tray in the UK) with parchment paper.
2. Make sure the food is dry. Pat dry washed fruit and blanched vegetables.
3. Spread the pieces out in one layer so they do not touch.
4. Freeze uncovered until solid. Berries take about 1 to 2 hours; larger items such as meatballs or dumplings take longer.
5. Move the frozen pieces into freezer bags or containers, press out the air, and label with the name and date.
6. Put them back in the freezer straight away, before they start to thaw.

How to tell it is done

Each piece should be hard all the way through and lift off the paper cleanly. If pieces bend or feel soft in the middle, give them more time.

Why it works

Food that freezes quickly forms small ice crystals, which damage the food less than the large crystals that form when food freezes slowly in a crowded bag. A single layer exposed to cold air freezes much faster than a lump. Each piece also gets a frozen surface before it touches the others, so they stay loose.

How to use it

Flash freezing works well for berries and sliced fruit, vegetables after you blanch and freeze them, meatballs, burger patties, dumplings, filled pasta, cookie dough balls and unbaked scones. Cook most of them straight from frozen and add a few minutes to the time.

Common mistakes

• Freezing wet fruit, which clumps and grows ice.
• Leaving food uncovered in the freezer for days, which causes freezer burn.
• Putting raw meat on a tray next to uncovered ready-to-eat food.
• Loading a warm, crowded freezer. Freeze a few trays at a time.