What freeze-dried food is, and how it differs from dried

Freeze-drying takes the water out of food while the water is still ice. It leaves the food’s own structure standing, full of tiny holes where the ice used to be, and that’s why a freeze-dried dish takes water back so quickly.¹

Frozen first, then the ice leaves as vapour

The trick is pressure. Below 0.01 °C and 0.612 kPa, the triple point of water, ice can’t melt; it can only turn into vapour.² Keep the food under both figures and the water leaves without the food ever getting wet again.

Step by step

1. Freeze

   The food is frozen at normal pressure until all its free water is ice.¹ We freeze ours below −30 °C before the vacuum starts.

2. Primary drying

   Temperature −25 to −20 °C

   The pressure drops far below the triple point and the shelves supply gentle heat. The ice sublimes and the vapour freezes again on a condenser at about −60 to −80 °C. It’s the longest stage and uses the most energy.¹

3. Secondary drying

   The water that never froze is drawn off while the food is warmed. For fruit and vegetables the product may reach 60–70 °C at this point.¹ The finished food holds under 5% water.¹

So it isn’t a cold process from start to finish, and nobody should call it raw. It’s drying at low temperature, with the heat kept below the point where the food would lose its shape.²

The idea is older than the camping shelf. Scientists were working on it at the turn of the twentieth century, and it became an industry in the Second World War, when blood plasma was freeze-dried on a large scale. For decades it was thought too expensive for food; freeze-dried coffee changed that.³

Freeze-dried against hot-air dried, line by line

“Dehydrated” on a label usually means dried in warm, moving air: a home dehydrator, or its industrial cousin. Both take the water out; the difference is in how, and you can feel it in the hand.

Neither is the safer method; the sources compare quality, not safety. Dried apricots and jerky are fine things. They just don’t turn back into dinner.

Light in the rucksack, a full bowl at the table

Raw food is 80–95% water.¹ Take nearly all of it out and the weight falls by a factor of five to twenty while the size barely changes, so a freeze-dried dish is light for its bulk.

Dry, from the pouch

With waterServing suggestion

Our Chicken & Rice weighs 150 g in the pouch. Add 400 ml of water and the bowl weighs the two together: you carry the food, and the water comes from the tap or the bottle when you want to eat. With water from the kettle it’s ready in 8 minutes; from the bottle, in about 20 minutes.

Not every dish goes both ways. The Porcini Mushroom Risotto takes the same water and the same minutes hot, but it’s hot water only. Which pouches work cold, and how long they take, is in cold or hot water.

One dish that works cold, one that needs the kettle

Pouch	Net weight	Water	Hot water	Cold water
Chicken & RiceLarge	150 g	400 ml	8 min	about 20 min
Porcini Mushroom RisottoLarge	150 g	400 ml	8 min	Hot water only

One dish that works cold, one that needs the kettle

• Chicken & RiceLarge

  Net weight

  150 g

  Water

  400 ml

  Hot water

  8 min

  Cold water

  about 20 min

• Porcini Mushroom RisottoLarge

  Net weight

  150 g

  Water

  400 ml

  Hot water

  8 min

  Cold water

  Hot water only

What freeze-drying doesn’t do

It doesn’t sterilise. Freeze-drying doesn’t kill bacteria; it puts them on hold, and they wake up when the water goes back in.⁹ That’s why food that needs cooking has to be cooked before it’s dried or after the water is added. Ours is cooked first, then freeze-dried whole, sauce and all, so the pouch holds a finished dish rather than a kit of ingredients.

It also doesn’t stop time. Oxygen, damp getting back in, light and fat that slowly turns rancid decide how long a dry food keeps,¹⁰ which is why each pouch carries its own date: the months are in how long freeze-dried food keeps. And what the process does to vitamins, with the measurements, is in what freeze-drying does to nutrients.

Our everyday dishes come in the Meals range, in a pouch sized for one lunch.

From our range

Chicken & RiceStandard

Cooked first, then freeze-dried whole: 300 ml of water and 8 minutes from the kettle.

€9.90See the chicken and rice