Freeze Drying – process and procedures

Food is best when served fresh. This is a common saying, and it is most true. But what about the professionals like soldiers and sailors and astronauts? They do not have the option to cook fresh food and eat it at its best. But this can be overcome by the use of some standard technology like freeze-drying.

What is freeze-drying?

Freeze drying is the process of preserving perishable material by removing the moisture content in it. It is a slow but effective process. It can be used to preserve any type of food. There are mainly three types of freeze dryers:

These classifications are based on the quantity of material that can be freeze-dried per hour in the freezers.

How is freeze-drying carried out?

Freeze drying is a simple but effective process and requires only minimum apparatus from quality vendors. To maintain the quality of perishable food items and certain types of edible drugs, it is best to remove the moisture content from them. This can be achieved by passing the food particles through three main procedures.

  1. Freezing
  2. Primary drying
  3. Secondary drying


The food item is frozen to a temperature below the triple point of the substances. Since biological material freezing can lead to a change in their structural characters, the food is rapidly cooled. This way the constituent properties like taste, nutrition, and quality of the food are not lost. This process can be carried out in a shell freezer or the compartment of a dry freezer.

Primary drying

This phase is also called sublimation. In this process, the pressure of the compartment is lowered, and steady heat is supplied. Care should be taken so as not to overheat, as it might affect the physical properties of the food material and result in damage to its molecular structure. This process is carried out in a very low vacuum so that the frozen water molecules directly convert to vapor.

Secondary Drying

Also called adsorption, this phase is responsible for the ionic-bond separation of water molecules from the food particles. This is achieved by increasing the temperature over the primary stage and breaking the ionic bonds.

If all the above processes are carried out in proper time and conditions, then around 1-5% moisture-free food particles can be packaged.

In short, to preserve perishable food, it is best to apply dry freezing technology from reputed companies.

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