Freeze-drying

Freeze drying, also known as lyophilisation 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. Freeze drying, also known as lyophilisation 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. Freeze drying results in a high quality product because of the low temperature used in processing. The original shape of the product is maintained and quality of the rehydrated product is excellent. Primary applications of freeze drying include biological (e.g., bacteria and yeasts), biomedical (e.g., surgical transplants), and food processing (e.g., coffee) and preservation. The first application of the freeze-drying process were in the Andes where indigenous people took low-land tubers up to high elevations and left them to freeze. Potatoes were squashed to evacuate water and, when left to freeze at night and exposed during the day, the mash would lose its remaining water while nutrients were preserved through the lyophilization process. This resulted in a food called chuño, with a long shelf life eaten well past its seasonal availability, that could be stored as emergency rations. Freeze drying as an industrial process began in as early as 1890 by Richard Altmann who devised a method to freeze dry tissues (either plant or animal), but went virtually unnoticed until the 1930s. In 1909, Shackell independently created the vacuum chamber by using an electrical pump. No further freeze drying information was documented until Tival in 1927 and Elser in 1934 had patented freeze drying systems with improvements to freezing and condenser steps. A significant turning point for freeze drying occurred during World War II. Blood plasma and penicillin were needed to treat the wounded in the field, and because of the lack of refrigerated transport, many serum supplies spoiled before reaching their recipients. 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. In the 1950s–1960s, freeze drying began to be viewed as a multi-purpose tool for both pharmaceuticals and food processing. Freeze-dried foods became a major component of astronaut and military rations. What began for astronaut crews as tubed meals and freeze-dried snacks that were difficult to rehydrate, were transformed into warm hot meals in space by improving the process of rehydrating freeze-dried meals with water. As technology and food processing improved, NASA looked for ways to provide a complete nutrient profile while reducing crumbs, disease-producing bacteria, and toxins. The complete nutrient profile was improved with the addition of an algae-based vegetable-like oil to add polyunsaturated fatty acids. Polyunsaturated fatty acids are beneficial in mental and vision development, and as it remains stable during space travel, can provide astronauts with its added benefits. The crumb problem was solved with the addition of a gelatin coating on the foods to lock in and prevent crumbs. Disease-producing bacteria and toxins were reduced by quality control and the development of the Hazard Analysis Critical Control Point (HACCP) plan, which is widely used today to evaluate food material before, during and after processing. With the combination of these three innovations, NASA could provide safe and wholesome foods to their crews from freeze-dried meals. Military rations have also come a long way, from being served spoiled pork and corn meal to beefsteak with mushroom gravy. How rations are chosen and developed are based on acceptance, nutrition, wholesomeness, producibility, cost, and sanitation. 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. The new tray rations (T Rations) which has been improved upon by increasing acceptable items and provide high quality meals while in the field. Freeze-dried coffee was also incorporated by replacing spray-dried coffee in the meal, ready-to-eat category.