Freeze drying

Primary applications of freeze drying include biological (e.g., bacteria and yeasts), biomedical (e.g., surgical transplants), food processing (e.g., coffee), and preservation.

The process involved multiple cycles of exposing potatoes to below freezing temperatures on mountain peaks in the Andes during the evening, and squeezing water out and drying them in the sunlight during the day.

[9] A significant turning point for freeze drying occurred during World War II when blood plasma and penicillin were needed to treat the wounded in the field.

[9] The freeze-drying process was developed as a commercial technique that enabled blood plasma and penicillin to be rendered chemically stable and viable without refrigeration.

[13] As technology and food processing improved, NASA looked for ways to provide a complete nutrient profile while reducing crumbs, disease-producing bacteria, and toxins.

[14] The complete nutrient profile was improved with the addition of an algae-based vegetable-like oil to add polyunsaturated fatty acids.

[14] Polyunsaturated fatty acids are beneficial in mental and vision development and, as they remain stable during space travel, can provide astronauts with added benefits.

[16] Additional requirements for rations include a minimum shelf life of three years, be deliverable by air, consumable in worldwide environments, and provide a complete nutritional profile.

Freeze dried pharmaceutical products are in most cases parenterals administered after reconstitution by injection which need to be sterile as well as free of impurity particles.

Afterwards the liquid is filled under sterile conditions into the final containers which in production scale freeze dryers are loaded automatically to the shelves.

It is important to note that, in this range of pressure, the heat is brought mainly by conduction or radiation; the convection effect is negligible, due to the low air density.

In addition, flavors, 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.

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.

Other freeze-dried biological products include antihemophilic factor VIII, interferon alfa, anti-blood clot medicine streptokinase, and wasp venom allergenic extract.

Examples of lyophilized biopharmaceuticals include blockbuster drugs such as etanercept (Enbrel by Amgen), infliximab (Remicade by Janssen Biotech), rituximab, and trastuzumab (Herceptin by Genentech).

Cell extracts that support cell-free biotechnology applications such as point-of-care diagnostics and biomanufacturing are also freeze-dried to improve stability under room temperature storage.

[4] 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.

[4] Because of its light weight per volume of reconstituted food, freeze-dried products are popular and convenient for hikers, as military rations, or astronaut meals.

The development of freeze drying increased meal and snack variety to include items like shrimp cocktail, chicken and vegetables, butterscotch pudding, and apple sauce.

Whole freeze-dried insects are sold as exotic pet food, bird feed, fish bait, and increasingly for human consumption.

[citation needed] In nanotechnology, freeze-drying is used for nanotube purification[30] to avoid aggregation due to capillary forces during regular thermal vaporization drying.

[1] When the product is successfully dried, packaged properly, and placed in ideal storage conditions the foods have a shelf life of greater than 12 months.

Since the main method of microbial decontamination for freeze drying is the low temperature dehydration process, spoilage organisms and pathogens resistant to these conditions can remain in the product.

Hence, to avoid this issue, mass spectrometers are used to identify vapors released by silicone oil to immediately take corrective action and prevent contamination of the product.

This system works to cool shelves and the process condenser by using compressors or liquid nitrogen, which will supply energy necessary for the product to freeze.

[citation needed] Additionally, the shelf-fluid system works to provide specific temperatures to the shelves during drying by pumping a fluid (usually silicone oil) at low pressure.

[2] Microwave-assisted freeze dryers utilize microwaves to allow for deeper penetration into the sample to expedite the sublimation and heating processes in freeze-drying.

This method can be complicated to set up and run as the microwaves can create an electrical field capable of causing gases in the sample chamber to become plasma.