Freeze drying

Freeze drying, also known as lyophilization or cryodesiccation, is a low temperature dehydration process that involves freezing the product, lowering pressure, then removing the ice by sublimation. This is in contrast to dehydration by most conventional methods that evaporate water using heat.

Process

The freeze drying process consists of three stages: pre-freezing, primary drying, and secondary drying.

Pre-freezing

In the pre-freezing stage, the material is cooled below its triple point, the lowest temperature at which the solid and liquid phases of the material can coexist. This ensures that sublimation rather than melting will occur in the following steps.

Primary drying

During the primary drying phase, the pressure is lowered and heat is added to the material in order for the water to sublimate. The amount of heat necessary can be calculated using the sublimation heat (the heat necessary to sublimate a certain amount of water).

Secondary drying

The secondary drying phase aims to remove any unfrozen water molecules, since the ice was removed in the primary drying phase. This part of the freeze-drying process is governed by the principles of desorption.

Applications

Freeze drying is used in a variety of sectors, from the pharmaceutical industry to the food industry. In the pharmaceutical industry, it is used to dry pharmaceuticals, biotechnology products, and diagnostic reagents. In the food industry, it is used to preserve food, improve its shelf life, and make it more convenient for transport.

Advantages and Disadvantages

The main advantage of freeze drying is that it maintains the structural integrity and preserves the nutritional content of the food or pharmaceutical product. However, the process is time-consuming and energy-intensive, which can make it more expensive than other drying methods.

See also

• Dehydration
• Sublimation (phase transition)
• Pharmaceutical industry
• Food industry