Why freeze-drying is the best method to preserve food?

Posted On January 4, 2022

Preserving food items has always been important to the human race. Especially in regions of vastly varying climatic conditions, it was seen that cultivation was not possible year-round and that some food material had to be stored safely.

But food is the most perishable item that it is, preserving food particles was a huge challenge. The knowledge that keeping food out of moisture and air can prolong its freshness led to many later discoveries. One of the most efficient and cost-effective inventions will be the small freeze dryer.

What is freeze-drying?

Freeze drying is the process of eliminating the presence of moisture and water molecules up to a minimum of 1-2% in food items and essential drugs to keep them fresh and edible for decades.

It is a food preservation technique that uses deep freezing and vacuum heating of food in various stages to preserve its nutrient value, freshness, and taste. It finds application in the military, aeronautics, marine field, and so on. For people who have to carry long supplies of food as the conditions they are working in are not favorable for cooking, preserved food is the only option.

What is the procedure for freeze-drying?

The freeze-drying of food for long-term preservation is carried out in three main steps:

• Freezing
• Primary drying or sublimation
• Secondary drying or adsorption

If all the above procedures are carried out in their optimum conditions and phase, then the moisture content at the molecular level can be reduced up to 98 percent.

Freezing

In this phase, the food particles are frozen rapidly in vacuum chambers. Cooling is carried out to a temperature below the triple point of the particles. This is done rapidly, keeping in mind the change in the structural composition of the food particles.

Primary drying or sublimation

In the sublimation process, the pressure of the whole chamber where the frozen food is kept is reduced to almost vacuum. This is accompanied by a gradual increase in temperature. Since heat is provided in a vacuum, the frozen water molecules will quickly sublime and evaporate. This vapor is collected and removed.

Secondary drying or adsorption

In adsorption, the ionic bonds of the water molecules are broken down by the application of higher temperatures in controlled conditions. This will effectively remove almost all the water content in the food and preserve it for a long time.

In short, freeze-drying is the best method to preserve food for long periods without losing its freshness and quality.