Freeze drying, also known as lyophilization or sublimation, they are synonymous. Freeze drying is a low temperature dehydrate process that typically used to preserve perishable materials, to extend shelf life, or make the material more convenient for storage or transport. Freeze drying works by freezing the material, then reducing the surround to allow the frozen water(ice) to sublimate.

Freeze dryer and lyophilizer are synonymous names for the same equipment. A freeze dryer executes a water removal process typically used to preserve perishable materials, to extend shelf life or make the material more convenient for transport. Freeze dryers work by freezing the material, then reducing the pressure and adding heat to allow the frozen water in the material to sublimate.

Freeze -drying is carried out using the principle of sublimation drying technique , the material to be dried is frozen rapidly at low temperature , and then under the appropriate vacuum , so that the sublimation of frozen water molecules directly into a steam escape process. Frozen the product was dried to obtain a lyophilisate called (lyophilizer), the process is called lyophilized (lyophilization).

Always in substance before drying at low temperature ( frozen ) , and ice crystals evenly distributed in the material , the sublimation process does not occur due to dehydration concentrated phenomenon , avoiding the side effects produced by vapor bubble oxidation. Dry material was dry porous sponge , is essentially the same volume , highly soluble in water and restitution. Prevention of dry matter in the physicochemical and biological variability maximum extent .

Freeze-drying machine is from the refrigeration system, vacuum system , heating system, electrical instrumentation control system components. The main part of the oven , a condenser , refrigeration units , pumps, heating / cooling devices . Its working principle is to be freeze -dried items to the triple point temperature, and then the articles under vacuum solid water ( ice ) sublimate directly into water vapor , are excluded from the article, the article dry. After the materials are processed before being sent to the freezing of frozen positions , and then into a dry warehouse sublimation dehydration , after the post-processing plant packaging. Vacuum sublimation drying warehouse system established low pressure conditions, the heating system to provide the latent heat of sublimation materials , refrigeration systems to provide the required amount of cold and dry ice condenser chamber . The device uses highly efficient radiant heating , the material is heated evenly ; efficient use of water-cooled trap to catch , and to achieve rapid defrost ; adopt efficient vacuum unit , and to achieve oil-water separator ; centralized refrigeration system using parallel , multi-channel on-demand cooling, working conditions stable , favorable energy efficiency ; using artificial intelligence control , high control accuracy , easy to operate.

Freeze-drying causes less damage to the substance than other dehydration methods using higher temperatures. Nutrient factors that are sensitive to heat are lost less in the process as compared to the processes incorporating heat treatment for drying purposes.Freeze-drying does not usually cause shrinkage or toughening of the material being dried. In addition, flavours, smells, and nutritional content generally remain unchanged, making the process popular for preserving food. However, water is not the only chemical capable of sublimation, and the loss of other volatile compounds such as acetic acid (vinegar) and alcohols can yield undesirable results.

Freeze-dried products can be rehydrated (reconstituted) much more quickly and easily because the process leaves microscopic pores. The pores are created by the ice crystals that sublimate, leaving gaps or pores in their place. This is especially important when it comes to pharmaceutical uses. Freeze-drying can also be used to increase the shelf life of some pharmaceuticals for many years.

Pharmaceutical companies often use freeze-drying to increase the shelf life of the products, such as live virus vaccines, biologics and other injectables. By removing the water from the material and sealing the material in a glass vial, the material can be easily stored, shipped, and later reconstituted to its original form for injection. Another example from the pharmaceutical industry is the use of freeze drying to produce tablets or wafers, the advantage of which is less excipient as well as a rapidly absorbed and easily administered dosage form.

Freeze-dried pharmaceutical products are produced as lyophilized powders for reconstitution in vials and more recently in prefilled syringes for self-administration by a patient.

Examples of lyophilized biological products include many vaccines such as live measles virus vaccine, typhoid vaccine, and meningococcal polysaccharide vaccine groups A and C combined. Other freeze-dried biological products include antihemophilic factor VIII, interferon alfa, anti-blood clot medicine streptokinase, and wasp venom allergenic extract.

Many bio-pharmaceutical products based on therapeutic proteins such as monoclonal antibodies require lyophilization for stability. Examples of lyophilized biopharmaceuticals include blockbuster drugs such as etanercept (Enbrel by Amgen), infliximab (Remicade by Janssen Biotech), rituximab, and trastuzumab (Herceptin by Genentech).

Freeze-drying is also used in manufacturing of raw materials for pharmaceutical products. Active Pharmaceutical Product Ingredients (APIs) are lyophilized to achieve chemical stability under room temperature storage. Bulk lyophilization of APIs is typically conducted using trays instead of glass vials.

Dry powders of probiotics are often produced by bulk freeze-drying of live microorganisms such as lactic acid bacteria and bifidobacteria.

The primary purpose of freeze drying within the food industry is to extend the shelf-life of the food while maintaining the quality.Freeze-drying is known to result in the highest quality of foods amongst all drying techniques because structural integrity is maintained along with preservation of flavors.Because freeze drying is expensive, it is used mainly with high-value products.Examples of high-value freeze-dried products are seasonal fruits and vegetables because of their limited availability, coffee, and foods used for military rations, astronauts/cosmonauts, and/or hikers

In chemical synthesis, products are often freeze-dried to make them more stable, or easier to dissolve in water for subsequent use.

In bioseparations, freeze-drying can be used also as a late-stage purification procedure, because it can effectively remove solvents. Furthermore, it is capable of concentrating substances with low molecular weights that are too small to be removed by a filtration membrane. Freeze-drying is a relatively expensive process. The equipment is about three times as expensive as the equipment used for other separation processes, and the high energy demands lead to high energy costs. Furthermore, freeze-drying also has a long process time, because the addition of too much heat to the material can cause melting or structural deformations. Therefore, freeze-drying is often reserved for materials that are heat-sensitive, such as proteins, enzymes, microorganisms, and blood plasma. The low operating temperature of the process leads to minimal damage of these heat-sensitive products.

In nanotechnology, freeze-drying is used for nanotube purification^[19] to avoid aggregation due to capillary forces during regular thermal vaporization drying.

Organizations such as the Document Conservation Laboratory at the United States National Archives and Records Administration (NARA) have done studies on freeze-drying as a recovery method of water-damaged books and documents. While recovery is possible, restoration quality depends on the material of the documents. If a document is made of a variety of materials, which have different absorption properties, expansion will occur at a non-uniform rate, which could lead to deformations. Water can also cause mold to grow or make inks bleed. In these cases, freeze-drying may not be an effective restoration method.

In bacteriology freeze-drying is used to conserve special strains.

In high-altitude environments, the low temperatures and pressures can sometimes produce natural mummies by a process of freeze-drying.

Advanced ceramics processes sometimes use freeze-drying to create a formable powder from a sprayed slurry mist. Freeze-drying creates softer particles with a more homogeneous chemical composition than traditional hot spray drying, but it is also more expensive.

A new form of burial which previously freeze-dries the body with liquid nitrogen has been developed by the Swedish company Promessa Organic AB, which puts it forward as an environmentally friendly alternative to traditional casket and cremation burials.