Freeze Drying

About Freeze Drying

Let’s answer your questions about Freeze Drying

What is freeze drying?

Freeze drying is a process where frozen moisture is removed under low pressure from a material (such as food). It’s done through sublimation so the water which is frozen is transitioned directly to a vapour skipping the liquid state.

How freeze drying works

1.

Freezing

It’s important that the food we are freeze drying is frozen solid first so that the sublimation can take place.

2.

Sublimation

The freeze dryer removes all the ice in a vacuum (low pressure). Approximately 99% of water is removed during this stage. It is a slow process to ensure that the food retains its structure and taste. The water that is removed is pumped out of the machine as it condenses.

3.

Adsorption

This phase ensures that the molecules that the water has been removed from stick to the food ensuring that as much flavour and nutrients are retained. It’s essentially a second drying phase.

The result… food that is shelf stable, retains almost all it’s original nutrients, enzymes, and flavours, and can be rehydrated quickly if required.

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What is the difference between freeze dried and deydrated?

The main difference between freeze dried and dehydrated is the method that is used to preserve the food. Freeze drying freezes the moisture and then slowly vacuums it out of the food. Dehydrating uses heat and fans to slowly draw out the moisture.

Due to using heat, dehydrating cannot preserve as many of the nutrients in the food as what freeze drying can.

Freeze dried foods are shelf stable for up to 25 years whereas dehydrated foods are generally only considered shelf stable for up to a year although some foods may last up to 5 years.

Are freeze dried foods healthy?

Freeze dried foods retain up to 98% of their original nutrients whilst weighing around 20% of their original weight.

Of course, if you are starting with a food that isn’t healthy then freeze drying it is not going to make it any healthier!

Freeze dried fruits and vegetables are almost the same as their natural form (only lighter) so they are a healthy option.

How does the weight of foods change when freeze dried?

Each individual item will have a different moisture content to start with, but you can expect freeze dried foods to be much lighter than before they were freeze dried – often weighing just 10% of its original weight.

For example, a kilo of fresh strawberries will usually become around 100 grams of freeze dried strawberries.

What foods cannot be freeze dried?

Most foods can safely be freeze dried however, there are a few foods that don’t cope so well with the freeze drying process including:

You’ll notice that a lot of these are quite oily foods which is the reason they don’t do so well in the freeze dryer – the water is removed but the oil remains, so you end up with an oily mess at the end!

If I have a food I want to preserve, will you freeze dry it for me?

We are happy to consider freeze drying your foods for you.

Of course, we will do any applicable research to ensure that it is safe to do so first and then provide you with a quote.

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