What is the Freeze Drying Method?

What is the Freeze Drying Method?

The main purpose of drying agricultural products; is to reduce their water content in order to minimize microbial spoilage and reactions during storage. Today, the newest drying method used in the food industry is Freeze-Drying, ie lyophilization, which is applied especially in fruits and vegetables. When this technique was used to make freeze-dried ice cream for NASA astronauts around the world, it became very popular, and the product obtained was also defined as astronaut food.

As consumers’ food preferences change and their economic concerns increase, consumers are increasingly in need of high-quality nutritious food products that they can easily purchase in stores. In recent years, consumers in the USA and European countries have become more demanding considering the quality and longevity potential in the supply of freeze-dried products.

The most important factor enabling the growth of the freeze-dried food market on a global basis is the superior quality of the final products compared to other food-drying technology products.

History of Freeze Drying

Freeze-drying (lyophilization), which is one of the methods that ensures the removal of water in products, is used in various fields, especially in the health and food industry. Although this method has become widespread in recent years and used with modern equipment, the history of the method is very old.

Centuries ago, Astek and Eskimos used this method to store their food. Inuit exposing the fish they caught to cold, dry Arctic winds blew the water off the fish. It is also known that the Incas used this method to dry meat in the low-oxygen atmosphere of the Altiplano plains in the Andes and under the radiant heat of the sun.

The use of the method in the laboratory environment took place towards the end of the 1880s. Until the 1930s, this method was used as a laboratory technique for processing heat-sensitive antibiotics and blood products.

Coffee was one of the first freeze-dried food products produced. In the 1950s, industrial freeze-drying of foods was introduced. Today, fresh fruits and vegetables with high water content, meat and dairy products, fish, medicinal plants, and pharmacological products can be successfully freeze-dried. However, this technique became more familiar when making freeze-dried ice cream for NASA astronauts.

Especially in the USA, it is understood that the number and variety of ‘freeze dry’ food products on the market shelves are increasing day by day, and their popularity is increasing. According to the sectors of the products in which the freeze-drying method is applied; food sector (coffee, plants, fruits, vitamins, extracts, animal products, etc.), pharmaceutical and biology sector (pharmaceuticals, enzymes, biological agents, cell and tissue applications, etc.), chemical sector, museum sector (books, wood, archaeological products, etc., by reducing the water content and recycling).

The Relationship of Frozen Products with the Market

The freeze-dried products market is proliferating. The main reason for the growth in the market; It is to obtain a higher quality and uniform product compared to other methods. Its use in foods with high added value and sensitive to heat is also becoming widespread day by day. With this drying method, the product closest to the fresh form is obtained in terms of nutritional value. Freeze-dried foods are the best-dried foods because of their superior texture and sensory quality after rehydration.

It is possible to obtain the product closest to the fresh form in terms of freeze-drying nutritional components. Freeze drying minimizes mineral, vitamin, and aroma losses in foods. The freeze-drying technique is the process of evaporating the water contained in the product before it becomes liquid by reducing the pressure in the environment after the product is first frozen. Freeze drying generally takes place in two steps.

First, the substance to be dried is frozen, and the water in the food turns into ice. The frozen material is then dried by sublimation of ice under reduced pressure. In order for sublimation to take place, the pressure of the system is reduced below the critical pressure, and the pressure is increased at the same time.

Since the water is removed from the product in a vacuum when it is in the solid phase, the product maintains its true shape, and there is no loss of volume. Freeze drying is applied on commercial scales for drying many valuable and heat-sensitive foods.

For example, the quality obtained in terms of color, aroma, and shape in freeze-dried strawberries cannot be achieved with other drying methods. With freeze drying, the product’s functional properties are preserved at the maximum level. Since the water in the food is in the ice phase at the point where it is in the drying stage, there is no liquid movement in the texture of the food, and thus, the food can maintain its true size and shape.

Thanks to the porous outer surfaces of freeze-dried foods, rehydration is easy, fast, and trouble-free, and clumping does not occur. The rehydrated cells survive at high rates and with low damage so that food can be fresh again.

Freeze drying provides a significant reduction in the weight of the food. Most foodstuffs, especially fruits, have a water content of around 80-90%. Therefore, when the high amount of water in the food is removed, the food becomes lighter, the transportation and storage costs decrease, and the circulation of the food becomes easier.

In addition, the moisture content of a freeze-dried food is 1-2% lower when compared to traditional drying methods. Freeze-dried foods typically contain 1-4% moisture, and their nutritional value is retained by 97%.

Shelf life of freeze-dried products can be up to 15-20 years when stored in suitable containers under normal room conditions and protected from light, preserving their nutritional values to a large extent. These products, which have lost about 90-95% of their weight, are an excellent alternative in activities such as camping, mountaineering, yachting, as well as in emergency stocks, in extraordinary situations such as war and natural disasters.

According to Mordor Intelligence, the global freeze-dried food market is growing 7.4% per year.

References: Ordu Provincial Directorate of Agriculture Food Safety Magazine (Year: 13 Issue: 34 July-December 2019)