Think about it, how often do you have the privilege of picking fresh fruit and eating it immediately? Fresh produce often loses plenty of its qualities during transport to the destination country. There is a solution though!

Have you ever heard of freeze-drying food? Have you ever wondered why lyophilised products are sometimes even healthier than their fresh counterparts from your local shop? Although freeze-drying appears to be a relatively new trend in food processing, it is a fairly old technique that is still considered one of the most effective methods of food preservation today.

What exactly is lyophilisation?

Lyophilisation, also known as freeze-drying, is a form of product preservation that removes all moisture and water from the product, leaving the basic structure and content of the material intact. Lyophilisation, also known as freeze-drying, is a low-temperature dehydration process that involves freezing the product, lowering the pressure and removing the ice from the product through sublimation.

Freeze-drying is a highly effective food preservation method that preserves all the nutrients, antioxidants, colour and flavour of ripe, seasonal food. Freeze-drying of fruits and other food products can also be used to separate and purify materials. Since freeze-drying occurs at temperatures below 48°C[T1] , such a product is considered a high-quality raw food.

One gets the impression that freeze-drying food is a relatively new process that has evolved with technological progress. The first attempts at freeze-drying were made as early as the 1990s. In the 19th century, Richard Altmann developed the method of freeze-drying tissues. He created a vacuum chamber powered by an electric pump. However, it was not until after the Second World War that the method was adopted for medical and commercial food processing.

What steps are taken in the freeze-drying of food?

Using the example of one of the most popular freeze-dried products – raspberries – let’s take a step-by-step look at how the process works.

1. Product collection

At the outset, you must obtain the product you want to freeze-dry. This is the most critical moment because you are now sourcing the raw material you will preserve. Regardless of the freeze-dryer’s quality, if the initial product is of a low grade, the end product will also remain so. Healthy food starts with sourcing raw materials.

2. Quality control

Before the production process begins, the raspberries undergo a thorough cleaning process. Organic products must undergo a thorough examination to ensure that no non-organic materials are present in the finished product. Organic raspberries are harvested in pristine, certified forests and go into a separate production line from other non-organic produce.

3. Freezing raspberries

The raspberries are transported to the freezer, where they are flash-frozen at an extremely low temperature. These temperatures reach as low as -46°C. If raspberries are frozen shortly after picking, much of the nutrient content will remain intact, thus preserving their full nutritional value.

4 . Lyophilisation

The frozen raspberries are then placed in a vacuum machine, which creates a powerful vacuum around the food, allowing the frozen solvent in the product to evaporate without going into a liquid phase. The sublimation process then begins. This means that the water contained in the food is transformed directly from a solid to a gaseous state. The sublimation process begins when the food particles gain enough energy to break free from the surrounding molecules. When the molecules have gathered enough energy to be liberated, yet the atmosphere is inadequate for forming a liquid state, water morphs from the solid state directly to the gaseous state, circumventing the liquid state. Water is removed from the food using a vacuum. This process ensures the raspberries retain their original nutritional value, good shape, colour and taste. The entire process takes about 20-36 hours.

5. Secondary drying

The subsequent process is sublimation drying, which involves dehydrating the raspberries to the desired and final moisture level. This is accomplished by reducing the pressure while simultaneously heating. Heating does not exceed 48°C, so the end product is still considered raw food. The final lyophilised product contains approximately 1-4% moisture. Removing moisture and water from food protects it from spoilage and extends its shelf life. Since the bulk of raw food is mainly water, expelling the water makes the food much lighter. That leaves only raspberries, which retain all the vitamins, minerals, antioxidants and other nutrients.

6. Packaging

When the product is sufficiently dried, it is sealed in moisture-proof packaging. When the packaging is secured, the product can have a shelf life of several years. The packaging should be sealed tightly to prevent air ingress even after opening. Ensure that the packaging is sealed properly after each use to prevent the product from clumping and to preserve the quality of the nutrients.

Though the lyophilisation process may appear straightforward, it can be complex in practice due to the specific requirements of various raw materials.

Through lyophilisation, raspberries can maintain their nutritional value and have a prolonged shelf life!

Why choose lyophilised food?

There are several benefits to choosing freeze-dried food. Lyophilisation is a versatile method of preservation. Almost any food can be freeze-dried, from fruit to full plates of dinner dishes.

Here are some of the benefits of choosing freeze-dried preserved foods:

  • The original nutritional value of lyophilised food is approximately 97%.
  • If you are seeking an exotic or rare food item, lyophilisation is the best solution! The product is harvested at its peak ripeness and immediately flash-frozen to retain its maximum nutritional value. When fruit is exported and transported long distances, the time involved to move it reduces the vitamin and nutrient content.
  • Lyophilisation preserves the original colour, taste, appearance and texture of food.
  • Freeze-dried food has a higher quality compared to other dehydration methods.
  • When placed in water, the product returns to its original state.
  • As a result, it has a longer shelf life.
  • The lightweight of this food makes it a popular choice for hikers and mountaineers.

Which is better: lyophilisation or dehydration?

Lyophilisation and dehydration are often compared. Both dehydration and lyophilisation are preservation methods that involve the removal of moisture. Lyophilisation consists of removing water and moisture by depressurisation, followed by eliminating ice by sublimation, while dehydration is the conventional method of evaporating water using heat.

Dehydration is an ancient method of food preservation. Dehydration means removing moisture and water from food as much as possible. People have been using this method for a long time, leaving food in the sun to dry out to ensure a longer shelf life.

Approximately 80-90% of the moisture is usually removed from dehydrated food, while lyophilisation removes around 98-99%, giving food a longer shelf life. Methods such as canning and drying use high temperatures that destroy most of the food’s nutritional value. Moreover, freeze-drying provides foods with a long shelf life of up to 20 years, whereas dehydrated, canned or frozen foods can only be stored for 2-4 years. To obtain the maximum amount of nutrients, the freeze-drying method is recommended. Dried fruit and lyophilised fruit are two different stories. Since freeze-dried food is not heated, it is considered raw food, containing all the properties of fresh food. During the drying process, up to 50% of the nutrients disappear with the water.