Freeze drying principle

It seems that freeze-drying is actually a technology that is not close to our lives. Actually, it is not. Many of our foods are processed using freeze-drying technology. For example, many of the dried fruits we often eat are processed using freeze-drying technology. So, why does freeze drying have such a drying effect? Let’s take a look at the principle of freeze drying.

From physics, we know that water has three phases, point O is the common point of the three phases, and OA is the melting point of ice. According to the principle that pressure decreases and boiling point decreases, as long as the pressure is below the triple point pressure, the moisture in the material can be sublimated directly from water to water vapor without passing through the liquid phase. According to this principle, the wet raw materials of food can be first frozen to below the freezing point to turn the water in the raw materials into solid ice. Then, in an appropriate vacuum environment, the ice can be directly converted into steam and removed. The water vapor can then be condensed using a water vapor condenser in the vacuum system to dry the material. This method of achieving drying by vacuum freezing is a process of physical change and movement of water, which occurs at low temperature and low pressure. Therefore, the basic principle of freeze-drying is the mechanism of heat and mass transfer at low temperature and low pressure.

Freeze drying is the process of removing water or other solvents from frozen biological products by sublimation. Sublimation refers to the process in which a solvent, such as water, changes directly from a solid state to a gaseous state without passing through a liquid state, like dry ice. The product obtained by freeze drying is called a lyophilizer, and the process is called lyophilization.

Why choose freeze drying?

While conventional drying can cause the material to shrink and damage cells, during freeze-drying the sample's structure is not destroyed because the solid components are held in place by the solid ice. As the ice sublimates, it leaves pores in the dry remaining material. This preserves the integrity of the product's biological and chemical structure and its activity. In the laboratory, freeze drying has many different uses. It is indispensable in many biochemical and pharmaceutical applications. It is used to obtain biological materials that can be stored for a long time, such as microbial cultures, enzymes, blood and drugs. In addition to long-term storage stability, it also retains its inherent biological activity and structure. For this reason, freeze drying is used to prepare tissue samples for structural studies (such as electron microscopy). Freeze drying is also used in chemical analysis, where it can produce samples in a dry state or concentrate samples to increase chemical sensitivity. Freeze-drying stabilizes sample composition without changing the chemical composition, making it an ideal analytical aid.

<<: What is the fastest way to remove formaldehyde?

>>: Does painted furniture contain formaldehyde?