What Is Vacuum Freeze-Drying, Anyway?

Freeze-drying sounds like science fiction, but the idea is simple: remove the water from food without cooking it.

Step 1: Freeze it

Fresh fruit is washed, cut and frozen quickly at very low temperatures. Freezing fast keeps ice crystals small, so the fruit keeps its structure.

Step 2: Lower the pressure

The frozen fruit goes into a vacuum chamber. At very low pressure, ice can turn straight into vapour without melting first. This is called sublimation.

Step 3: Gentle warming

A little heat helps the ice sublimate. The vapour is collected on a very cold condenser, and slowly almost all the water is gone.

What’s left?

A piece of fruit that looks almost like the original but weighs a fraction as much. It has:

• Its natural colour, since there’s no browning from high heat
• A crisp, airy crunch from the tiny spaces the ice left behind
• Concentrated flavour, because the water is gone but the taste stays

Because there’s so little moisture left, freeze-dried fruit keeps for a long time in a sealed pack at room temperature.

Once opened, keep the pack tightly sealed. Freeze-dried fruit loves moisture and will lose its crunch if left open.