The science
No preservatives. No fridge. Still good for a year.
That's a fair thing to be sceptical about, so here's the actual reason. Food spoils because microbes — bacteria, mould, yeast — grow on it. Microbes need water to grow. Take the water out of the food, and they can't grow on it, no matter how long it sits in a packet.
That's the whole trick. Every food preservation method is some version of this: canning cooks the microbes dead and seals them out, freezing slows them to a halt, salt and sugar pull water out of their cells, and chemical preservatives poison them. Freeze-drying just removes the water itself. Once the food drops below about 3% moisture, there's no liquid water left for microbes to live in, so the food stays safe at room temperature.
The hard part is removing the water without ruining the food in the process. That's what freeze-drying actually solves — and it does it with physics, not chemistry. Here's how, in three stages.
01
Freezing
The cooked food goes onto stainless-steel shelves and the chamber is dropped to about −40 °C. The water inside the food crystallises into ice.
How fast you freeze matters. Slow freezing grows large ice crystals that puncture cell walls — the texture you get from a freezer-burned vegetable. We freeze fast enough that the crystals stay small, which leaves the cell structure mostly intact. That's part of why a rehydrated meal still has bite to it instead of falling apart into mush.
02
Sublimation (primary drying)
Now the trick. The chamber stays cold and the pressure is pulled down to roughly 0.5–1 mbar — about a thousandth of atmospheric pressure. At that pressure, water can't exist as a liquid at all: the ice goes straight to water vapour without ever melting. That phase change is called sublimation.
A gentle amount of heat (well below cooking temperatures) is added through the shelves to keep the sublimation going. The vapour drifts off the food, travels to a much colder condenser elsewhere in the chamber, and freezes back onto it as ice. Around 95% of the water in the food is removed during this phase. It takes hours.
Because the food never gets warm and never goes through liquid water, the proteins, oils, vitamins and cell structure aren't damaged the way a second cook or a microwave would damage them.
03
Desorption (secondary drying)
After primary drying, around 5% of the water is still in the food — not as ice, but as water molecules "bound" to proteins, starches and sugars. That's still enough water for microbes to eventually grow on.
So the shelf temperature is raised slightly (still nowhere near cooking temperatures) and the vacuum is held. The bound water desorbs from those molecules and is carried out of the chamber. The finished product holds under 3% moisture — dry enough that bacteria, mould and yeast can't grow on it. No preservatives needed, no refrigeration needed. Just a sealed pack.
What freeze-drying does
What comes out at the end is a porous, intact, room-temperature-stable version of the meal that went in. Most of its volume is now empty space where the ice used to be. When you pour hot water in, water rushes back into that pore network and the food rehydrates from the inside out — which is why six minutes is enough to bring it back to the texture it came out of the pan with.
What that means for you
- Under 3% moisture — too dry for microbes, no preservatives needed
- Never cooked twice — vitamins, oils and proteins stay intact
- Cell structure preserved — real texture on rehydration
