How do you freeze dry food?

Freeze Dried Fruit is a delicious and nutritious snack. There is a huge range of freeze dried food available on the market, but what exactly is it?

Freeze drying, technically called lyophilisation, is the removal of moisture whilst the product is in a frozen state and under a vacuum. The original product is frozen to around -20 degrees C and placed on trays in a vacuum chamber. The atmospheric pressure is lowered using vacuum pumps, which has the effect of lowering the boiling point of water. In our machines, water actually boils at -20 degrees C! The water vapour literally boils out of the fruit (whilst frozen so it is cold, not hot), which is called sublimation. We’ve come a long way, but we haven’t got freeze dried food yet! The water vapour is then captured on frozen pipes at the end of the freeze drier that are at -40 degrees C or colder. After about 24 hours, all of the moisture in the product has migrated to the pipes (called the condenser) and formed a solid block of ice. Now we finally have some freeze dried fruit or other freeze dried snacks. The product is now completely dry but retains its colour, shape and nutritional value - almost identical to the fresh product. This is due to the low temperature of the freeze drying process. Volatile antioxidants and vitamins like vitamin C are preserved in the product. With a moisture level of less than 4%, the product is stable and if stored correctly can last for decades with virtually no detrimental effects.

Benefits of freeze dried food

Apart from the fact that freeze dried fruit and freeze dried snacks are delicious, there are a range of practical reasons that you might freeze dry food. It can improve shelf life, reduce the weight of products and add a unique texture unlike no other.

Freeze dried ice cream was created under contract for NASA to allow astronauts to take the delicious treat into space with them (Although it is unclear if the freeze dried ice cream ever made it into space). It was developed as a way of prolonging the shelf life of food, removing the need for refrigeration, and removing all the water weight to reduce weight on the spacecraft.

Check out this picture of one of our new mammoth freeze dryers